₦airaland Forum

RyanAutomotive:
Good evening sir.

Thank you for the detailed explanation. Let’s go through this carefully before any major AC components are replaced unnecessarily.


🔎 Professional Diagnostic Insight

Vehicle: Toyota Corolla 2013

Your main symptom is very important:

• AC cools well in the morning
• Cooling becomes weak when the sun is hot

This pattern usually points to heat-load or system efficiency issues, not necessarily immediate compressor failure.

Let’s break down the technician’s points.


1️⃣ Compressor “Cannot Be Repaired” Claim

Your 2013 Corolla uses a variable displacement compressor.

Many technicians in Nigeria call it “automatic compressor” because it does not use a traditional magnetic clutch coil like older compressors.

However, this does NOT automatically mean the compressor must be replaced.

In many cases the issue may be:
• Weak compressor control valve
• Low refrigerant charge
• Condenser airflow issue
• High system pressure due to heat

A proper diagnosis should confirm pressure readings first before recommending compressor replacement.


2️⃣ AC Radiator (Condenser) Has Oil Deposits

Oil inside the condenser can happen when:
• A compressor had internal wear
• The system was previously opened
• Oil migrated through the system

However, if the car truly had recent service in the US as of October 2025, a heavily contaminated condenser would be unusual unless:

• There was a leak repair
• A compressor was previously replaced
• The system was improperly serviced

This needs confirmation before replacing parts.


⚠️ Important Observation

If the compressor was truly failing internally, you would typically notice:

• AC becoming weak both morning and afternoon
• Noise from compressor
• Metal contamination in the system
• Poor cooling at idle

Since your AC still cools well in the morning, it suggests the system still has some healthy compression.

That means the problem could instead be:

• Weak condenser cooling under high heat
• Cooling fan efficiency issue
• Slightly low refrigerant level
• Dirty condenser fins restricting airflow
• Expansion valve efficiency

These are far more common in Nigeria’s hot weather.


📌 What Should Be Checked First

Before replacing compressor or condenser, a proper AC diagnosis should include:

1️⃣ High and low pressure gauge test
2️⃣ Condenser airflow inspection (fan speed and airflow)
3️⃣ Refrigerant level verification
4️⃣ Temperature drop test at vents
5️⃣ Compressor control valve operation

Without these checks, replacing parts becomes trial and error.


🎯 Professional Take

Your technician may not necessarily be wrong, but the diagnosis sounds incomplete.

Replacing compressor + condenser together is a major repair, and it should only be recommended after pressure testing confirms compressor inefficiency or internal contamination.

Given the vehicle just entered Nigeria recently with a service history, it is reasonable to verify the diagnosis with proper AC system testing before spending money.


🏢 Ryan Automotive Limited Recommendation

Before replacing the compressor and condenser, ensure a proper AC pressure and performance diagnosis is carried out.

This will confirm whether the issue is truly compressor-related or simply cooling efficiency under heavy heat load, which is very common in Nigeria.


If you are in Lagos or able to bring the vehicle down, Ryan Automotive Limited carries out structured AC and vehicle diagnostics to avoid unnecessary part replacements.


Precision • Transparency • Excellence

Ryan Automotive Limited
Automotive Diagnostics | Cooling System Assessment | Professional Repair Approach 🚗🔧

Thank you. I am in Lagos. I will give prompt you on WhatsApp.

Hi everyone, I’m looking for some technical insight on a persistent fuel consumption issue (currently getting only 10 MPG) on my 2006 Honda Civic. I have already restored the cooling fan to factory settings and installed a new thermostat, but P0128(thermostat below regulating temperature) keeps returning and the car vibrates. I have confirmed that the vibration is not coming from my mounts.



I performed a cold-start test today with my scanner to watch the Short Term Fuel Trim (STFT) vs. Coolant Temp (ECT). Here is the data:

At 34°C (Startup): Upper radiator hose was at ambient temp. STFT was extremely rich, fluctuating between -12% and -22%.

At 60°C: The upper radiator hose became very hot and untouchable.

At 96°C: Cooling fans triggered normally. STFT finally stabilized between -3% and -5%. LTFT immediately improved from -20% to -17%. Engine load also revolves around 36% at iidle

My Analysis:
Since the upper hose is getting hot at only 60°C, I suspect the new thermostat is opening much too early or stuck open (it should stay closed until ~78°C I guess). This seems to be keeping the car in "cold-start" enrichment mode for too long, causing the massive negative fuel trims and poor MPG.

I previously had other codes pointing to the EGR valve and ECT sensor which I sorted by replacing the part's and codes disappeared

My Questions :

Given that the trims improve once the car finally hits 96°C, am I right to assume the thermostat is the "smoking gun"?

My local "rewire" says I can only find "Tokunbo" (used) parts thermostat , but I’m worried about reliability. Has anyone had success with specific aftermarket brands for the R18 engine, or is OEM the only way to clear P0128?

Could this "rich" condition be the cause of a heavy vibration that worsens when the AC is turned on?

Thanks for the help! abeg, I dey average like 2 miles per liter of FUEL. I don tire

haykay2005:
Hi everyone, I’m looking for some technical insight on a persistent fuel consumption issue (currently getting only 10 MPG) on my 2006 Honda Civic. I have already restored the cooling fan to factory settings and installed a new thermostat, but P0128(thermostat below regulating temperature) keeps returning and the car vibrates. I have confirmed that the vibration is not coming from my mounts.



I performed a cold-start test today with my scanner to watch the Short Term Fuel Trim (STFT) vs. Coolant Temp (ECT). Here is the data:

At 34°C (Startup): Upper radiator hose was at ambient temp. STFT was extremely rich, fluctuating between -12% and -22%.

At 60°C: The upper radiator hose became very hot and untouchable.

At 96°C: Cooling fans triggered normally. STFT finally stabilized between -3% and -5%. LTFT immediately improved from -20% to -17%. Engine load also revolves around 36% at iidle

My Analysis:
Since the upper hose is getting hot at only 60°C, I suspect the new thermostat is opening much too early or stuck open (it should stay closed until ~78°C I guess). This seems to be keeping the car in "cold-start" enrichment mode for too long, causing the massive negative fuel trims and poor MPG.

I previously had other codes pointing to the EGR valve and ECT sensor which I sorted by replacing the part's and codes disappeared

My Questions :

Given that the trims improve once the car finally hits 96°C, am I right to assume the thermostat is the "smoking gun"?

My local "rewire" says I can only find "Tokunbo" (used) parts thermostat , but I’m worried about reliability. Has anyone had success with specific aftermarket brands for the R18 engine, or is OEM the only way to clear P0128?

Could this "rich" condition be the cause of a heavy vibration that worsens when the AC is turned on?

Thanks for the help! abeg, I dey average like 2 miles per liter of FUEL. I don tire

Good morning sir,

Thank you for the detailed explanation and data. Let’s go through this step by step before anything is replaced unnecessarily.

⸻

🔎 Professional Diagnostic Insight – Honda Civic 2006 P0128 / Fuel Consumption Issue

Vehicle: Honda Civic 2006 (R18 Engine)
Symptom: Poor fuel consumption (~10 MPG), P0128 code, engine vibration, STFT/LTFT fluctuations

1️⃣ P0128 – Thermostat Below Regulating Temperature
• Your cold-start data strongly suggests the thermostat is opening too early.
• A thermostat stuck open or opening prematurely keeps the engine longer in enrichment mode, which explains:
• Extremely negative STFT (-12% to -22%)
• Poor fuel economy (~2 mpg / 10 MPG)
• Rich mixture causing vibration
• The fact that fuel trims stabilize once the engine reaches ~96°C confirms that the ECU is waiting for proper coolant temperature to normalize fuel mixture.

⸻

2️⃣ Thermostat Replacement Considerations
• Tokunbo (used) thermostats may work temporarily but reliability is uncertain and can cause recurring P0128 or even overheating if they stick closed.
• For the R18 engine, OEM thermostat is highly recommended to ensure:
• Proper opening temperature (~78–82°C)
• Consistent engine management
• Long-term fuel efficiency

⸻

3️⃣ Rich Mixture and Vibration Correlation
• Yes, the rich condition from prolonged cold-start mode can cause vibration at idle and under load.
• Turning the AC on increases engine load, which can exacerbate the vibration, especially with high negative fuel trims.
• Other causes of vibration (mounts, misfires, spark plugs, intake leaks) should be secondary considerations since you’ve already ruled out mounts and EGR/ECT codes.

⸻

📌 What Should Be Done Now

1️⃣ Replace the thermostat with a reliable OEM unit.
2️⃣ Flush the coolant if it has been contaminated during previous checks or parts replacement.
3️⃣ Verify proper STFT/LTFT behavior after installation.
4️⃣ Confirm vibration and MPG improve once engine reaches normal operating temperature.

⸻

🎯 Professional Take
• Based on your scanner data, the thermostat is indeed the likely “smoking gun”.
• Using unreliable used parts may result in repeated P0128 and continued poor fuel consumption.
• Proper thermostat replacement should normalize fuel trims, reduce rich condition vibration, and restore reasonable MPG.

⸻

🏢 Ryan Automotive Limited Recommendation
• Focus on replacing the thermostat with a quality OEM unit first, then monitor fuel trims and engine behavior.
• This structured approach avoids unnecessary guesswork and costly repeated part replacements.
• Proper diagnostics and corrective action here will restore fuel efficiency and smooth operation of your Civic.

⸻

Precision • Transparency • Excellence
Ryan Automotive Limited
Automotive Diagnostics | Engine Management Assessment | Professional Repair Approach 🚗🔧

Good day fellow Nairalanders, Please I need help,I just bought this Chevrolet Aveo 2010 Nigerian use though the car is very sound and I have done the necessary servicing of the vehicle but I notice the car consume too much fuel for a 4plug.Imagine a 20k fuel from sandfill Oniru to Ikotun and I’m already on empty tank and also it displays a hold sign on the dashboard which I have tried to turn off beside the gear but it doesn’t go off.

Iamdiamond01:
Good day fellow Nairalanders, Please I need help,I just bought this Chevrolet Aveo 2010 Nigerian use though the car is very sound and I have done the necessary servicing of the vehicle but I notice the car consume too much fuel for a 4plug.Imagine a 20k fuel from sandfill Oniru to Ikotun and I’m already on empty tank and also it displays a hold sign on the dashboard which I have tried to turn off beside the gear but it doesn’t go off.

Have you scanned the car completely to know what's the cause of the 'Hold' or the cause of the abysmal fuel economy?

Good evening gurus. I have this code on my acura tsx 2004.

How do I solve this?

The car revs up and down when this code is triggered and looses power.

My 2013 Ford Edge battery drains every night even when I ensure everything including the lights are turned off, please what could be the cause.

llade:
My 2013 Ford Edge battery drains every night even when I ensure everything including the lights are turned off, please what could be the cause.

You need to carry out parasitic draw test to find out whats draining you battery. If you're in Abuja feel free to contact me.

I use a 2014 Honda crosstour
The check engine light popped up
I scanned and got a P0420 and P0430 error code
I bought and installed all those O2 sensor adaptors on the upstream O2 sensor for bank 1 and 2.
The error code is still there
pls I need help here

cosd:
I use a 2014 Honda crosstour
The check engine light popped up
I scanned and got a P0420 and P0430 error code
I bought and installed all those O2 sensor adaptors on the upstream O2 sensor for bank 1 and 2.
The error code is still there
pls I need help here

You are suppose to put a adaptors you bought on d lower sensor after the catalyst not be4 the catalyst.

Good afternoon everyone…please my car Camry 2013 just show ABS light, Traction Control light and parking Brake light all together on the dashboard….please what could cause this and what should be the solution and who will be the technician to repair it…mechanic or Rewire

TUBLEZ:
Good day gurus in the house

My car Honda accord 2012 is shorting oil badly and no leakages anywhere, then i notice when I start it in the morning it brings out whitish/blue smoke 💨 for like 2 minutes then disappears. If I change oil now in less than 1 week it’s already very low

V6?

3KINGZ18:
V6?

4 plug

AmazingG007:
Good afternoon everyone…please my car Camry 2013 just show ABS light, Traction Control light and parking Brake light all together on the dashboard….please what could cause this and what should be the solution and who will be the technician to repair it…mechanic or Rewire

Scan the car to know what wrong drop scan codes

AmazingG007:
Good afternoon everyone…please my car Camry 2013 just show ABS light, Traction Control light and parking Brake light all together on the dashboard….please what could cause this and what should be the solution and who will be the technician to repair it…mechanic or Rewire

Either really, first you need to scan the vehicle to ascertain why they are turned on, if you are in Lagos I could do that for you

I use a 2004 Ford Taurus se, It always misfiring 3 months after changing plugs and servicing the nozzles. Though I have it converted to cng which I use simultaneously.
What should be done to at least extend this 3 months period.

kingreign:
This is a thread created for people to tell us their vehicle faults and we on our part can give solutions to their car faults. Where applicable, we may make references using pictures, videos and others to provide answers and solutions.

Please, state the name, model and year of your car, type of transmission and engine, and the location of the car to enable quicker response.

Happy motoring!

egestarch009:
I use a 2004 Ford Taurus se, It always misfiring 3 months after changing plugs and servicing the nozzles. Though I have it converted to cng which I use simultaneously.
What should be done to at least extend this 3 months period.

Discontinue the use of the CNG for the mean time, and observe what happens then report back.

If meko has changed the fibre b4,nw why that kick dey occur,if not u don go buy fake gear oil

onyii255:
Greetings my people..

I have an issue with my 2012 Camry. I noticed yesterday that the R sign on the dashboard blinks when I engage the reverse gear and the vehicle jerks when the reverse gear is engaged as well.

I don’t experience that kick when I shift to Drive, it only occurs when Reverse is engaged.

What’s could be the issue please??

I want to upgrade my 2008 highlander to 2012 any advice ?

Horbar1:
I want to upgrade my 2008 highlander to 2012 any advice ?

It's doable. Feel free if you have the finance to back it up. Its your choice and your money 🙂

Horbar1:
I want to upgrade my 2008 highlander to 2012 any advice ?

I’ll advise not to do this type of upgrade I’ll share below, if you ply bad roads often from my little experience they end up dropping and they aren’t too strong.
Also be careful who would do this upgrade when it comes to your vehicles headlamp wiring.
But if you’re doing the normal 012 upgrade I don’t think you have any issues

Please my Hyundai Elantra 2017 just goes off in motion without any warning but comes immediately back on like nothing happened when I restart it. The car doesn't overheat. And it drives normally after going off. The first time it happened, I was in traffic for a very long time and I felt that was it. But it has happened two more times in the space of 1 week. What could be the issue and how can I solve it?

Virgo01:
Please my Hyundai Elantra 2017 just goes off in motion without any warning but comes immediately back on like nothing happened when I restart it. The car doesn't overheat. And it drives normally after going off. The first time it happened, I was in traffic for a very long time and I felt that was it. But it has happened two more times in the space of 1 week. What could be the issue and how can I solve it?

Good Afternoon sir.

Thank you for bringing this up. A vehicle going off while in motion is something that should be taken seriously, even if it restarts immediately and drives normally afterward. Let’s look at this properly.



🔎 Professional Diagnostic Insight

Vehicle: Hyundai Elantra 2017
Symptom: Engine shuts off while driving, then restarts and operates normally.

This type of issue usually falls into three main technical areas: electrical power interruption, sensor signal loss, or fuel delivery interruption.


1️⃣ Crankshaft Position Sensor Interruption

One of the most common causes of sudden engine shutdown while driving is a failing crankshaft position sensor.

This sensor tells the engine computer:
• Engine speed
• Crankshaft position
• When to fire spark and inject fuel

If the signal briefly drops:
• The ECU immediately shuts the engine down for safety
• Once the sensor reconnects or cools down, the engine restarts normally

This often happens randomly and without warning, especially when the sensor begins to fail.



2️⃣ Electrical Power Supply Interruption

Another possible cause is momentary electrical power loss.

Areas that must be checked include:
• Battery terminals
• Engine ground points
• Ignition switch
• Main engine relay
• Fuse box contacts

A weak connection or worn relay can momentarily interrupt power to the ECU, which will instantly shut off the engine.

Once power returns, the car behaves as if nothing happened.



3️⃣ Fuel System Interruption

A fuel pump or fuel pump relay issue can also produce similar symptoms.

If the fuel pump stops briefly:
• Fuel pressure drops
• Engine stalls instantly

After restarting, the pump primes again and the vehicle drives normally.

This can sometimes occur more frequently during long traffic situations or heat soak conditions.



⚠️ Important Observation

You mentioned the first occurrence happened during heavy traffic.

This is important because high engine bay temperature can expose weaknesses in:
• Sensors
• Relays
• Electrical connections

When these components heat up, internal resistance can increase and cause intermittent failure.



📌 What Should Be Checked First

Before replacing any parts, proper diagnostics should include:

1️⃣ Full vehicle scan for stored or pending fault codes
2️⃣ Live data monitoring of crankshaft and camshaft signals
3️⃣ Electrical load and grounding inspection
4️⃣ Fuel pressure test while running
5️⃣ Inspection of ignition switch and main relay circuits

These checks allow the exact cause to be identified instead of guessing.



🚨 Do Not Ignore This Issue

Even though the car restarts immediately, a stall while driving can be dangerous because:

• Power steering assistance is lost
• Brake assist becomes weaker
• The vehicle could stall at high speed or in heavy traffic

Early diagnosis prevents a potentially risky situation.



🎯 Professional Take

Intermittent shutdown problems like this are usually electrical or sensor-related, and they often start exactly the way you described — rare at first, then gradually becoming more frequent.

The earlier the fault is properly diagnosed, the easier and cheaper it is to resolve.

Waiting until it becomes a permanent stall can lead to roadside breakdowns.



🏢 Ryan Automotive Limited Recommendation

The best step now is structured diagnostic scanning and electrical system testing to pinpoint whether the issue is related to:

• Crankshaft position sensor
• Main relay or ignition power supply
• Fuel pump control circuit

Once confirmed, the repair becomes precise rather than trial and error.

If you are within Lagos or able to bring the vehicle down, Ryan Automotive Limited carries out professional vehicle diagnostics and fault isolation to identify intermittent faults like this accurately.

We attend to vehicles from different locations, and proper diagnosis will help ensure the issue is fixed permanently rather than temporarily.



Precision • Transparency • Excellence

Ryan Automotive Limited
Automotive Diagnostics | Engine & Electrical Fault Analysis | Professional Repair Approach 🚗🔧

Virgo01:
Please my Hyundai Elantra 2017 just goes off in motion without any warning but comes immediately back on like nothing happened when I restart it. The car doesn't overheat. And it drives normally after going off. The first time it happened, I was in traffic for a very long time and I felt that was it. But it has happened two more times in the space of 1 week. What could be the issue and how can I solve it?

It’ll need physical assessment

Louiscars:
It’ll need physical assessment

Alright thank you.

accelion:
Good afternoon. I need help with running a smoke test to detect a vacuum leak in Honda Accord 2013. Is there anywhere I can do this in Lagos on the mainland? Thanks.

Hi,
How were you able to solve this

accelion:
Good afternoon. I need help with running a smoke test to detect a vacuum leak in Honda Accord 2013. Is there anywhere I can do this in Lagos on the mainland? Thanks.

Hi,
How were you able to solve this problem
Thanks a lot

Good afternoon, kingreign,

Please wondering what could be issue, corrola makes a loud sound while driving, while accelerating, moment speedometer read 30 upwards,I've checked exhaust, no issue..
Has normal sound starting, not until engage movement and acceleration gets 30 upward..

obisite:
Good afternoon, kingreign,

Please wondering what could be issue, corrola makes a loud sound while driving, while accelerating, moment speedometer read 30 upwards,I've checked exhaust, no issue..
Has normal sound starting, not until engage movement and acceleration gets 30 upward..

I can not tell what's the reason behind the noise unless you bring it let me diagnose and carry out test drives to isolate the noise origin.

Guys, please I need your advice. The transmission of my Rx350 2013 is slipping. It stalled at the second gear. I took it for a scan and it threw up fault code P0715 (input Turbine/speed control sensor A). A gear master has changed this sensor and the car now selects all 6 gears. But I discovered that it still slips between gear 1 and 2. It easily selects other gears. The gear master is advising me to change the TCM that it might be the culprit. We have scanned and rescanned and there's no more fault codes from the gear. I read on Google that we need to reset the TCM, yet, the gear master says he has calibrated the car. I'm a little at lost on what to do next. Kindly advise.

Profesoh:
Guys, please I need your advice. The transmission of my Rx350 2013 is slipping. It stalled at the second gear. I took it for a scan and it threw up fault code P0715 (input Turbine/speed control sensor A). A gear master has changed this sensor and the car now selects all 6 gears. But I discovered that it still slips between gear 1 and 2. It easily selects other gears. The gear master is advising me to change the TCM that it might be the culprit. We have scanned and rescanned and there's no more fault codes from the gear. I read on Google that we need to reset the TCM, yet, the gear master says he has calibrated the car. I'm a little at lost on what to do next. Kindly advise.

Good morning sir.

Thank you for the detailed explanation. Transmission issues like this require a very careful and structured diagnostic approach, especially on modern Lexus vehicles. Let’s examine the situation properly before any expensive components like the TCM are replaced.

⸻

🔎 Professional Diagnostic Insight

Vehicle: Lexus RX350 2013
Initial Fault Code: P0715 – Input/Turbine Speed Sensor “A” Circuit

This sensor monitors the speed of the transmission input shaft and sends that information to the Transmission Control Module (TCM) so the system can determine:

• Correct gear engagement
• Shift timing
• Torque converter operation
• Hydraulic pressure control

When the sensor fails or sends incorrect data, the transmission may:

• Get stuck in a specific gear
• Shift erratically
• Enter a protective fail-safe mode

Replacing the sensor was the correct first step, and the fact that the vehicle now selects all six gears again indicates that the original fault was likely addressed.

However, the remaining slip between gear 1 and 2 suggests there may still be an underlying issue.

⸻

1️⃣ Residual Adaptation / Calibration Issue

After replacing certain transmission components or sensors, the transmission computer may still retain old adaptive learning values.

These stored values affect:

• Shift pressure
• Clutch engagement timing
• Gear transition behavior

If they are not properly reset using a professional diagnostic scanner, the transmission may continue to behave incorrectly.

A proper TCM adaptive reset and relearn procedure is sometimes required.

⸻

2️⃣ Valve Body or Solenoid Performance

If the slipping occurs only between gear 1 and 2, this may indicate a hydraulic control issue within the valve body assembly.

Possible causes include:

• Weak or sticking shift solenoid
• Hydraulic pressure imbalance
• Internal valve body wear

These issues may not always trigger fault codes, especially if the system still manages to complete the shift.

⸻

3️⃣ Transmission Fluid Condition

Transmission slipping can also occur when:

• Fluid is degraded or burnt
• Incorrect fluid type is used
• Fluid level is not correctly set at operating temperature

The RX350 transmission is very sensitive to fluid condition, and improper servicing can affect gear engagement.

⸻

4️⃣ TCM Replacement Consideration

Replacing the Transmission Control Module (TCM) should always be the last step, not the first.

In practice, TCM failure on this model is much less common than:

• Valve body issues
• Solenoid performance problems
• Fluid pressure imbalance
• Incomplete adaptation reset

Therefore, replacing the TCM without confirming these areas can lead to unnecessary expense without solving the problem.

⸻

⚠️ Important Observation

The absence of fault codes does not always mean the transmission is perfectly healthy.

Many hydraulic or mechanical issues occur without immediately triggering diagnostic codes, especially when the system still manages to shift through the gears.

⸻

📌 What Should Be Checked Next

Before considering TCM replacement, the following should be done:

1️⃣ Perform a complete transmission live-data analysis
2️⃣ Verify transmission fluid condition and level
3️⃣ Perform a proper TCM adaptive reset and relearn procedure
4️⃣ Test shift solenoid response and hydraulic pressure behavior
5️⃣ Inspect the valve body assembly if slipping persists

This approach ensures the exact cause is identified rather than replacing parts based on assumption.

⸻

🎯 Professional Take

From experience with Lexus RX transmissions, slipping between 1st and 2nd gear after sensor replacement is more commonly related to adaptation or valve body control, not the TCM itself.

Proper diagnostic testing will determine whether the issue is electronic calibration or hydraulic control.

Addressing it early helps prevent further internal clutch wear.

⸻

🏢 Ryan Automotive Limited Recommendation

At this stage, the vehicle should undergo structured transmission diagnostics, including live data analysis and adaptive system reset, before any major component replacement.

This ensures the exact source of the slipping is identified and resolved correctly.

If you are able to bring the vehicle down, Ryan Automotive Limited performs professional transmission diagnostics and fault isolation to accurately determine whether the issue lies with calibration, solenoids, or internal hydraulic control.

This avoids unnecessary replacement of expensive components like the TCM.

⸻

Precision • Transparency • Excellence

Ryan Automotive Limited
Transmission Diagnostics | Fault Code Analysis | Professional Repair Approach 🚗🔧

haykay2005:
Hi everyone, I’m looking for some technical insight on a persistent fuel consumption issue (currently getting only 10 MPG) on my 2006 Honda Civic. I have already restored the cooling fan to factory settings and installed a new thermostat, but P0128(thermostat below regulating temperature) keeps returning and the car vibrates. I have confirmed that the vibration is not coming from my mounts.



I performed a cold-start test today with my scanner to watch the Short Term Fuel Trim (STFT) vs. Coolant Temp (ECT). Here is the data:

At 34°C (Startup): Upper radiator hose was at ambient temp. STFT was extremely rich, fluctuating between -12% and -22%.

At 60°C: The upper radiator hose became very hot and untouchable.

At 96°C: Cooling fans triggered normally. STFT finally stabilized between -3% and -5%. LTFT immediately improved from -20% to -17%. Engine load also revolves around 36% at iidle

My Analysis:
Since the upper hose is getting hot at only 60°C, I suspect the new thermostat is opening much too early or stuck open (it should stay closed until ~78°C I guess). This seems to be keeping the car in "cold-start" enrichment mode for too long, causing the massive negative fuel trims and poor MPG.

I previously had other codes pointing to the EGR valve and ECT sensor which I sorted by replacing the part's and codes disappeared

My Questions :

Given that the trims improve once the car finally hits 96°C, am I right to assume the thermostat is the "smoking gun"?

My local "rewire" says I can only find "Tokunbo" (used) parts thermostat , but I’m worried about reliability. Has anyone had success with specific aftermarket brands for the R18 engine, or is OEM the only way to clear P0128?

Could this "rich" condition be the cause of a heavy vibration that worsens when the AC is turned on?

Thanks for the help! abeg, I dey average like 2 miles per liter of FUEL. I don tire

Except you want to order an after Market thermostat, your option for now is to try a few more "Belgium" thermostats.

Nice fault analysis you got there by the way.