I scanned my 05 Accord b4 I took delivery of it and it gave me this code: P0141 which was Oxygen sensor heater circuit Bank 1 Sensor 2. I checked it online and saw that the sensor is to be replaced. When i started driving the car, I noticed it was consuming a lot of fuel. It was checked and observed that there was no Catalytic converter. I bought one and it was fixed, meanwhile the check-engine light was still on.

Afterwards, we began trouble-shooting the sensor issues because of the high-fuel consumption, after much checks here and there, and to cut long story short, the mechanic said the problem is not the Sensor, that it is the Brain Box, that the area controlling the the Sensor in the brain box is bad. He said I should buy a new brain box. This car drives very fine, everything works perfectly except for my "perceived" high-fuel consumption, very low mileage, looks like brand new and just 2 weeks old on major use. Now I am wondering how the brain box could have gone bad and if it was bad, would it still be giving out error codes?

The mechanic in question seems to be sure of what he said but I want to read the opinions of informed auto technicians here before doing anything further.

Please share ur ideas on this.

Summary:

Honda Accord 2005 toks
Check Engine light on
Scanned result: P0141 (Oxygen Sensor)
Car consumes fuel
Catalytic converter installed
Sensor said to be alright and hence not solved.
Check engine still on
Mech says the problem is brain box and needs to be changed
Car still consumes fuel

Help!

Have you changed the oxygen sensor and see if the check engine light goes off and also improve fuel consumption??

For 2005 honda accord, the sensor not expensive. Sold by shops for 3-5k I think.

you Dd not solve the 02 sensor problem. so you can't make a conclusion.besides I have seen some place where they will give you the brain box to test drive on your car. if you are convinced that it the problem with your car..you can go ahead and pay and by doing that you don't spend your money on unwanted parts.

sholatech: Have you changed the oxygen sensor and see if the check engine light goes off and also improve fuel consumption??

For 2005 honda accord, the sensor not expensive. Sold by shops for 3-5k I think.

Thanks a lot! The guy said he tested the sensor in the car, that it is good but my concern is if it is good, why then did the car return a code that has to do with the sensor?

Ogojohn: you Dd not solve the 02 sensor problem. so you can't make a conclusion.besides I have seen some place where they will give you the brain box to test drive on your car. if you are convinced that it the problem with your car..you can go ahead and pay and by doing that you don't spend your money on unwanted parts.

The guy said the sensor is ok that even if we change it that the code will still be there and the fuel issue will persist. He says changing the brain box will correct everything. While I do not want to doubt this, I have to be very careful of changing the brain box of a very sound car I have barely even used and which did not return any brain box code when scanned. The mech says that the brain box will not return codes since it is not ok but then why did it return the P0141 code?

Siena, Ikenna et al, where art thou? Pls visit this thread.

I am happy you have doubts about your mech's position. If the guy is sure the problem is brain-box, he should fix a working one to prove his point period. You don't just ask someone to change brainbox like that.

BluStreak: I am happy you have doubts about your mech's position. If the guy is sure the problem is brain-box, he should fix a working one to prove his point period. You don't just ask someone to change brainbox like that.

Thanks a lot!

Have d same issue. Mine is a toyoota camry with code P1135 meaning aair fuel sensor malfunction bank1 sensor 1. The mechanic said the brain box is faulty dat I should change it. Buut if d brain box is fualty won't d car begin to mibehave. Well mine still gets good gas mileage as I get 323 miles on a full tank aas opposed to 416 miles. Any suggestionm

mich2012:

Thanks a lot! The guy said he tested the sensor in the car, that it is good but my concern is if it is good, why then did the car return a code that has to do with the sensor?




The guy said the sensor is ok that even if we change it that the code will still be there and the fuel issue will persist. He says changing the brain box will correct everything. While I do not want to doubt this, I have to be very careful of changing the brain box of a very sound car I have barely even used and which did not return any brain box code when scanned. The mech says that the brain box will not return codes since it is not ok but then why did it return the P0141 code?

run away from the mechanic s/he is not good it is hard to test the sensor if you are not good with electronics all you need is to change the sensor which is being said is faulty by the ECU. just know that ECUs very rarely mafunction after changing the ECU will get the proper signal from the sensor and the ECU will do proper adjustment and your car's fuel consumption will improve thats sensor is for reading whether the fuel is to rich or not and correct adjustment will be done by the ECU the reason for that is for saving the planet from carbon monoxides etc and saving the world fuel by not wasting

speed001: Have d same issue. Mine is a toyoota camry with code P1135 meaning aair fuel sensor malfunction bank1 sensor 1. The mechanic said the brain box is faulty dat I should change it. Buut if d brain box is fualty won't d car begin to mibehave. Well mine still gets good gas mileage as I get 323 miles on a full tank aas opposed to 416 miles. Any suggestionm

if a code if pulled out and it points to something it means the pointed sensor is faulty, why say it is the ECU when the ECU has told you that this sensor is faulty. get your sensor changed and clear the code you will get good mileage

but let me inform if your car manual says you do 416 miles it means at certain speed and certain driving patterns, eg the load of the car your driving chnaging gear at the right time etc

speed001: Have d same issue. Mine is a toyoota camry with code P1135 meaning aair fuel sensor malfunction bank1 sensor 1. The mechanic said the brain box is faulty dat I should change it. Buut if d brain box is fualty won't d car begin to mibehave. Well mine still gets good gas mileage as I get 323 miles on a full tank aas opposed to 416 miles. Any suggestionm

Sorry Bro, guess we have to stay glued to this thread then. Do you get that mileage with AC on and city drive?
I wish the mods will help push it to front page.

ZIM DRILL:

run away from the mechanic s/he is not good it is hard to test the sensor if you are not good with electronics all you need is to change the sensor which is being said is faulty by the ECU. just know that ECUs very rarely mafunction after changing the ECU will get the proper signal from the sensor and the ECU will do proper adjustment and your car's fuel consumption will improve thats sensor is for reading whether the fuel is to rich or not and correct adjustment will be done by the ECU the reason for that is for saving the planet from carbon monoxides etc and saving the world fuel by not wasting

Thanks a lot. He uses a repair manual which he also used during the diagnosis and also a nice mech but this brain box issue is strange to me to be honest. Thanks once more!

mich2012:

Sorry Bro, guess we have to stay glued to this thread then. Do you get that mileage with AC on and city drive?
I wish the mods will help push it to front page.




Thanks a lot. He uses a repair manual which he also used during the diagnosis and also a nice mech but this brain box issue is strange to me to be honest. Thanks once more!

repair manual on most cases tell you which spanners to use and how to take off the part but some guide you on testing voltage or resistance but if s/he is not good with electronic reading voltage, resistance etc then that guide wont be any use to him/her, s/he ends up blaming the ECU instead of replacing he sensor which is being said to be faulty

ZIM DRILL:

repair manual on most cases tell you which spanners to use and how to take off the part but some guide you on testing voltage or resistance but if s/he is not good with electronic reading voltage, resistance etc then that guide wont be any use to him/her, s/he ends up blaming the ECU instead of replacing he sensor which is being said to be faulty

Thanks a lot ZIM. Are you an auto mech/technician?

mich2012:

Thanks a lot ZIM. Are you an auto mech/technician?

am more into electronics but i do mechanics with a friend

@ michs its all city driving o and @ times I use the airconditioner but nt all d time. I've changed the sensor but the code refused to go. I bought d sensor new and changed it but it did nt work m the electrician tested tone stuff wit tester and said no current dere or sumfin. Inputs needed

Here is some knowledge for you, the oxygen sensor you are referring to, which is the lower one, has ABSOLUTELY NO BEARING on fuel consumption.
The one on top (air/fuel ratio sensor) is the one that controls inputs to your injectors and can affect fuel economy.
You have proven what I have said countless times on this site and elsewhere, the absence/presence of a catalyst also has no bearing on fuel economy. They are placed there to regulate exhaust emissions into the atmosphere, nothing more, nothing less.
Whatever solution you come up with to take off the CEL will not affect your "perceived poor fuel economy".
I am not sure I read anywhere in this thread that you have ACTUALLY replaced the sensor in question. If that is so, I would wonder why. Also note that it may not be the sensor at fault but the connection at the socket of the sensor.

speed001: @ michs its all city driving o and @ times I use the airconditioner but nt all d time. I've changed the sensor but the code refused to go. I bought d sensor new and changed it but it did nt work m the electrician tested tone stuff wit tester and said no current dere or sumfin. Inputs needed

ok! Same thing with mine, they tested it with 2 or 3 sensors and said none is working, that the brain box is not supplying current to the connector or so.

nissparts: Here is some knowledge for you, the oxygen sensor you are referring to, which is the lower one, has ABSOLUTELY NO BEARING on fuel consumption.
The one on top (air/fuel ratio sensor) is the one that controls inputs to your injectors and can affect fuel economy.
You have proven what I have said countless times on this site and elsewhere, the absence/presence of a catalyst also has no bearing on fuel economy. They are placed there to regulate exhaust emissions into the atmosphere, nothing more, nothing less.
Whatever solution you come up with to take off the CEL will not affect your "perceived poor fuel economy".
I am not sure I read anywhere in this thread that you have ACTUALLY replaced the sensor in question. If that is so, I would wonder why. Also note that it may not be the sensor at fault but the connection at the socket of the sensor.

Thanks nissparts, the guy has checked it and said no need changing it.

Pls reply with possible solution. Thanx

speed001: @ michs its all city driving o and @ times I use the airconditioner but nt all d time. I've changed the sensor but the code refused to go. I bought d sensor new and changed it but it did nt work m the electrician tested tone stuff wit tester and said no current dere or sumfin. Inputs needed

the code doesnt go by putting the new part, 1st clear the code from the ECU memory aka scanning and erasing the code then put the new part, some people put the part 1st then scan and erase code

when the car runs the ECU it will get correcr readings signals from the part and no code will register aka Check Engine since correct signals are be recieved by the ECU aka brain box

so your can only need erasing the code aka scan and erase if the same code comes back then the new part is faulty

nissparts: Here is some knowledge for you, the oxygen sensor you are referring to, which is the lower one, has ABSOLUTELY NO BEARING on fuel consumption.
The one on top (air/fuel ratio sensor) is the one that controls inputs to your injectors and can affect fuel economy.
You have proven what I have said countless times on this site and elsewhere, the absence/presence of a catalyst also has no bearing on fuel economy. They are placed there to regulate exhaust emissions into the atmosphere, nothing more, nothing less.
Whatever solution you come up with to take off the CEL will not affect your "perceived poor fuel economy".
I am not sure I read anywhere in this thread that you have ACTUALLY replaced the sensor in question. If that is so, I would wonder why. Also note that it may not be the sensor at fault but the connection at the socket of the sensor.

you are wrong

http://en.wikipedia.org/wiki/Oxygen_sensor

Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, if the air–fuel ratio of a combustion engine is rich or lean. Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or the fuel entering the engine. But when information from oxygen sensors is coupled with information from other sources, it can be used to indirectly determine the air-fuel ratio. Closed loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to enabling electronic fuel injection to work efficiently, this emissions control technique can reduce the amounts of both unburnt fuel and oxides of nitrogen entering the atmosphere. Unburnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of combustion chamber temperatures exceeding 1,300 kelvin due to excess air in the fuel mixture and contribute to smog and acid rain. Volvo was the first automobile manufacturer to employ this technology in the late 1970s, along with the three-way catalyst used in the catalytic converter.

Thanks Zim for the explanation

Hello.
This code indicates a fault in the heater circuit (either open or short), Usually it is an open circuit due to a faulty heater element in the sensor (sensor 2, after cat). This sensor measures catalytic converter efficiency and generally does not affect your short term fuel trim (everyday driving), although it can have an impact on overall fuel curve efficiency (long term fuel trim). This is another topic though.

Get a multimeter and check the resistance (Ohms) between the two black wires. If it gives you infinite Ohms the sensor is bad. If the sensor checks out ok check the 12volt circuit to the heater element. There will be a heater fuse in line. The ECM (engine control module) feeds current (12 v and ground) to the two black wires in open loop mode (cold start). Your problem will lie in the feed circuit (short/open), oxygen sensor (element open).

PLEASE DO NOT start by replacing the ECM. You must ensure all the above checks are complete and NO FAULT is found in them. The internal ECM circuit can only be deemed faulty if it is NOT SUPPLYING OUT 12v to the feed (heater) circuit. The system wiring has to be thoroughly and carefully traced. Honda ECM's are generally trouble free and occasionally fail.

This bring up another question regarding your catalytic converter. You mentioned the vehicle did not have a catalytic converter? Is this vehicle an in line 4 cylinder (K24) motor? Since it's toks means it has been imported from the US I assume? A catalytic converter should have been in place.

Did you notice a difference in fuel consumption before and after replacing the converter. Is the fuel consumption better or worse?

I wish to also shed some light on catalytic converters and fuel consumption.

It seems there is a mis-conception that catalytic converters have no effect on fuel consumption. Catalytic converters are placed in modern vehicles to reduce emissions to an acceptable level without affecting engine performance and fuel consumption. Converters use two types of catalysts to reduce HC (unburnt fuel), CO (Carbon Monoxide) and NOx (oxides of Nitrogen), caused by high combustion temperature. One is a reduction catalyst and another type is an oxidation catalyst. To keep it brief these materials keep the emission out of the tail pipe to a minimal. The sensor 2 (after cat) is a short range sensor which detects oxygen content in the exhaust by feeding a rapid fluctuating voltage back to the ECM. This determines exhaust efficiency and long term fuel trim. Very crucial for overall running efficiency of modern engines.

Now think of an engine as a BIG AIR PUMP. All vehicle's on the road today have a certain amount of exhaust back pressure built into them determined by intake and exhaust system designs (exhaust headers, straight pipes (A & B), catalytic converters and exhaust muffler). As efficiently as an engine breathes in (air intake), it must breathe out (exhaust) as effectively (free flow) to maintain maximum efficiency and peak engine performance. A healthy operational engine works at it's peak efficiency at an A/F (air/fuel) ratio of 14:6 to 1.

Now any restriction in the intake or exhaust system immediately affects engine back pressure and affects perfect combustion. This in turn alters the air/fuel ratio: hence affecting the fuel curve. Restrictions can be caused by a clogged air filter, in tank fuel filter, etc and exhaust system components.

I will take the catalytic converter in this example:

A plugged or blocked catalytic converter reduces the air flow of exhaust from the engine. This causes excess exhaust build up in the engine which reduces the amount of new combustible oxygen the engine is able to pull in (intake). This restriction reduces efficiency. The engine (exampled as an air pump) now has to work harder to gain speed. This increased work LOWERS FUEL ECONOMY (the ECM shifts to a rich fuel map as it is not receiving accurate information from respective air metering sensors (MAP, air flow meter etc). Excess fuel is dumped into the engine signaled by a longer injector duty cycle (on time), from the ECM. The engine needs the excess fuel to propel the vehicle along as the speed increases, despite of restricted airflow. The engine will run, but sluggishly due to the inadequate air flow and at the expense of EXCESS FUEL CONSUMPTION. A plugged catalytic may also cause an engine to cough after short operation.

There is really a lot more on this topic to keep your engine running at its optimum level.

Good luck with resolving the issue on your Accord.

Regards

md_autotec: Hello.
This code indicates a fault in the heater circuit (either open or short), Usually it is an open circuit due to a faulty heater element in the sensor (sensor 2, after cat). This sensor measures catalytic converter efficiency and generally does not affect your short term fuel trim (everyday driving), although it can have an impact on overall fuel curve efficiency (long term fuel trim). This is another topic though.

Get a multimeter and check the resistance (Ohms) between the two black wires. If it gives you infinite Ohms the sensor is bad. If the sensor checks out ok check the 12volt circuit to the heater element. There will be a heater fuse in line. The ECM (engine control module) feeds current (12 v and ground) to the two black wires in open loop mode (cold start). Your problem will lie in the feed circuit (short/open), oxygen sensor (element open).

PLEASE DO NOT start by replacing the ECM. You must ensure all the above checks are complete and NO FAULT is found in them. The internal ECM circuit can only be deemed faulty if it is NOT SUPPLYING OUT 12v to the feed (heater) circuit. The system wiring has to be thoroughly and carefully traced. Honda ECM's are generally trouble free and occasionally fail.

This bring up another question regarding your catalytic converter. You mentioned the vehicle did not have a catalytic converter? Is this vehicle an in line 4 cylinder (K24) motor? Since it's toks means it has been imported from the US I assume? A catalytic converter should have been in place.

Did you notice a difference in fuel consumption before and after replacing the converter. Is the fuel consumption better or worse?

I wish to also shed some light on catalytic converters and fuel consumption.

It seems there is a mis-conception that catalytic converters have no effect on fuel consumption. Catalytic converters are placed in modern vehicles to reduce emissions to an acceptable level without affecting engine performance and fuel consumption. Converters use two types of catalysts to reduce HC (unburnt fuel), CO (Carbon Monoxide) and NOx (oxides of Nitrogen), caused by high combustion temperature. One is a reduction catalyst and another type is an oxidation catalyst. To keep it brief these materials keep the emission out of the tail pipe to a minimal. The sensor 2 (after cat) is a short range sensor which detects oxygen content in the exhaust by feeding a rapid fluctuating voltage back to the ECM. This determines exhaust efficiency and long term fuel trim. Very crucial for overall running efficiency of modern engines.

Now think of an engine as a BIG AIR PUMP. All vehicle's on the road today have a certain amount of exhaust back pressure built into them determined by intake and exhaust system designs (exhaust headers, straight pipes (A & B), catalytic converters and exhaust muffler). As efficiently as an engine breathes in (air intake), it must breathe out (exhaust) as effectively (free flow) to maintain maximum efficiency and peak engine performance. A healthy operational engine works at it's peak efficiency at an A/F (air/fuel) ratio of 14:6 to 1.

Now any restriction in the intake or exhaust system immediately affects engine back pressure and affects perfect combustion. This in turn alters the air/fuel ratio: hence affecting the fuel curve. Restrictions can be caused by a clogged air filter, in tank fuel filter, etc and exhaust system components.

I will take the catalytic converter in this example:

A plugged or blocked catalytic converter reduces the air flow of exhaust from the engine. This causes excess exhaust build up in the engine which reduces the amount of new combustible oxygen the engine is able to pull in (intake). This restriction reduces efficiency. The engine (exampled as an air pump) now has to work harder to gain speed. This increased work LOWERS FUEL ECONOMY (the ECM shifts to a rich fuel map as it is not receiving accurate information from respective air metering sensors (MAP, air flow meter etc). Excess fuel is dumped into the engine signaled by a longer injector duty cycle (on time), from the ECM. The engine needs the excess fuel to propel the vehicle along as the speed increases, despite of restricted airflow. The engine will run, but sluggishly due to the inadequate air flow and at the expense of EXCESS FUEL CONSUMPTION. A plugged catalytic may also cause an engine to cough after short operation.

There is really a lot more on this topic to keep your engine running at its optimum level.

Good luck with resolving the issue on your Accord.

Regards

Thanks a lot for taking your time to write such a piece, I gained a lot. Pls drop your contact details

To your questions, it's an I4, yes imported from the US. I don't know where the converter was taken out, in the States or at our Port (most likely)

After the installation of the converter, sincerely, I did not notice any improved fuel economy though it may be a thing of the mind.

The mech seems to have checked the voltage things with his repair manual before arriving at the conclusion but I still feel I do not have to change the ECM.

You are welcome! I will check tomorrow whether I may have a step by step diagnosis procedure lying somewhere for this code, which your mechanic may follow. It really shouldn't be complicated.

Please drop me an email on md_autos@yahoo.com

Regards

The only time a cat converter will affect fuel economy is when it is plugged up. There will be no difference if you remove one that is not blocked.
Zim, it appears you do not appreciate the difference between the oxygen sensor before the catalyst and the one right after it which is the one the OP is concerned with and which primarily just measures the efficiency of the catalyst.

md_autotec: You are welcome! I will check tomorrow whether I may have a step by step diagnosis procedure lying somewhere for this code, which your mechanic may follow. It really shouldn't be complicated.

Please drop me an email on md_autos@yahoo.com

Regards

Thank you Sir, I will be grateful for any help you can render. I will shoot you a mail

More comments and tips pls

change the sensor first..sensors are cheap less than $60.....but remeber to erase the chk engine light first..ecu faults dont give the symtoms that ur car is giving

cretin: change the sensor first..sensors are cheap less than $60.....but remeber to erase the chk engine light first..ecu faults dont give the symtoms that ur car is giving

Thanks but the guys said they have tested the sensor and it's ok but I will heed to ur advice and see what happens

r u techincal?..u can check the sensors urself......unplu it from the harness and use a multimeter to read the terminals..it has 4 wires 1 pair is the actual sensor, while the other pair is the heaster circuit...its the heater circuit that usually fails....so the semi ignorant mechanic just checks n says the sensor is ok, without really knowing what they r doing!!!!!.......they told me the same thing when i had a bad oxygen sensor on my car..they fiddled with it, n after a while told me that the sensor is ok....when i insisted they said OGA UR CAR STILL MOVES, CONTINUE DRIVING IT LIKE THAT..NO WORRY URSELF!.......i insisted and scanned the car...the scan told me the exact sensor that was bad..[since my car has 4 sensors], i even went to toyota place n they didnt hv the sensor........i imported the sensor from usa and changed it out...n the check engine light is off.....those sensors usually fail after about 100k miles..so be prepared to change all of them...cos they usually fail 1 after the other, once the reach the service ceiling/life

Cretin where r u