I have a faulty piece of electronics in my vehicle and one of the testS I need to do is to test for continuity between one of the pinouts and body ground.

I know my way around a multi-meter and have successfully tested for continuity between the PCM and the equipment at fault.

What I cannot do is to test for continuity between one of the pins and body ground because I do not know where to find body ground.

Please kindly help me find this elusive fellow? BODY GROUND!



LOL

THANKS

Body ground is the any metal part around the vehicle which is grounded or connected to the negative battery terminals. Ground in vehicle is like the Earth in the building electricals terms

Body ground is the any metal part around the vehicle which is grounded or connected to the negative battery terminals. Ground in vehicle is like the Earth in the building electricals terms.

TUDEXautoCARE:
Body ground is the any metal part around the vehicle which is grounded or connected to the negative battery terminals. Ground in vehicle is like the Earth in the building electricals terms.

Thanks so much.

So based on your explanation above and the extract below:

SHORT CIRCUITS

A short circuit occurs when electricity finds a short cut" from positive to negative; it is the result of a bare spot on the wire contacting part of the metal car body. The windings in electric motors can also short. Short circuits are hazardous be- cause they create sparks, burned wires, and blown fuses. They are more difficult to locate with a test light than open circuits.

1. Disconnect the suspected circuit at all points where it is joined by connectors (you'll need the wiring diagram for this).

2. Attach the clamp of the tester to the hot side of that circuit's fuse and touch the probe to the other side of the blown fuse. If the light goes on, the short is between the fuse and the first disconnected connector.

3. If the light doesn't go on, connect the first connector and touch the probe to the fuse holders again. If the light goes on, the short is between the first and second connector.

4. If the light again does not go on, repeat the process until the section of the wire with the short is isolated.

Which I have taken from this site: http://www.drivegreen.com/Auto_Service_5_Wiring_Lighting.htm

Can I safely cut out the part of the wires that go into the wiring harness from the engine compartment into the passenger area where the PCM is located and run new wires from the PCM to the component, provided that I ensure that each wire goes exactly into where I cut the old one everything should work?

Cause I can see that three different wires are shorted:
1. power supply is shorted to body ground
2. Monitor Signal to PCM is shorted
3. Monitor Signal ground is shorted

If I can get wires that match the colors of the pre-existing wires and run them from the component to the PCM all should be ok?

The I have isolated the fault to between the PCM and a connector, from the other connector end to the component is all clear?

Looking forward to your further comments

FEGEITOK:


Thanks so much.

So based on your explanation above and the extract below:

SHORT CIRCUITS

A short circuit occurs when electricity finds a short cut" from positive to negative; it is the result of a bare spot on the wire contacting part of the metal car body. The windings in electric motors can also short. Short circuits are hazardous be- cause they create sparks, burned wires, and blown fuses. They are more difficult to locate with a test light than open circuits.

1. Disconnect the suspected circuit at all points where it is joined by connectors (you'll need the wiring diagram for this).

2. Attach the clamp of the tester to the hot side of that circuit's fuse and touch the probe to the other side of the blown fuse. If the light goes on, the short is between the fuse and the first disconnected connector.

3. If the light doesn't go on, connect the first connector and touch the probe to the fuse holders again. If the light goes on, the short is between the first and second connector.

4. If the light again does not go on, repeat the process until the section of the wire with the short is isolated.

Which I have taken from this site: http://www.drivegreen.com/Auto_Service_5_Wiring_Lighting.htm

Can I safely cut out the part of the wires that go into the wiring harness from the engine compartment into the passenger area where the PCM is located and run new wires from the PCM to the component, provided that I ensure that each wire goes exactly into where I cut the old one everything should work?

Cause I can see that three different wires are shorted:
1. power supply is shorted to body ground
2. Monitor Signal to PCM is shorted
3. Monitor Signal ground is shorted

If I can get wires that match the colors of the pre-existing wires and run them from the component to the PCM all should be ok?

The I have isolated the fault to between the PCM and a connector, from the other connector end to the component is all clear?

Looking forward to your further comments

just use a wiring diagram, which can be downloaded free from bbbind.com. But try to repair the original wires first, if it is impossible to repair then you can rout another wire.

cocoduck:
just use a wiring diagram, which can be downloaded free from bbbind.com. But try to repair the original wires first, if it is impossible to repair then you can rout another wire.

I have a wiring diagram, and indeed I have been using it.

This is opportunity cost, I really want to repair the original wires but the route they are taking between the engine and component requires I remove the entire engine and the dashboard just get at them not to talk of fixing them.

The more components that need to be taken out and but back the greater the potential of causing some trouble, and I am not a mechanic...LOL

So I would rather cut the wires a few inches from the PCM and run new wires through insulation through the firewall to the component.

Indeed as they say short circuits are hard to find, open circuits are so easy to find.

Am not using a test light but a multi-meter.

As this is my first time, I am naturally cautious since I do not wish to cause any further damage in the name of solving a problem.

FEGEITOK:


I have a wiring diagram, and indeed I have been using it.

This is opportunity cost, I really want to repair the original wires but the route they are taking between the engine and component requires I remove the entire engine and the dashboard just get at them not to talk of fixing them.

The more components that need to be taken out and but back the greater the potential of causing some trouble, and I am not a mechanic...LOL

So I would rather cut the wires a few inches from the PCM and run new wires through insulation through the firewall to the component.

Indeed as they say short circuits are hard to find, open circuits are so easy to find.

Am not using a test light but a multi-meter.

As this is my first time, I am naturally cautious since I do not wish to cause any further damage in the name of solving a problem.

I suggest you take it to somebody that has the tools to disassemble the dashboard and you do the repairs yourself, or if you have the tools, you can try it your self, disconnect the battery first, before attempting it, start from the steering wheel, then remove the components and label or mark them so you can easily put them back, then go to the radio and use pry bars (plastic preferably) to pry those panels, they rarely use screws to hold them, they use tabs instead, then remove the glove box then the passenger air bags, take your time to find the screws, they are usually hidden from view, or under some panels, the main dash is held by 15 or 16mm nuts.
You will need patience, lots of it, to be able to bring this thing down, common sense is also required a lot, and if you can, do it with somebody, mark and label every nut and bolt and screw and every other thing, so that you will easily figure it out when you assemble it .

cocoduck:
I suggest you take it to somebody that has the tools to disassemble the dashboard and you do the repairs yourself, or if you have the tools, you can try it your self, disconnect the battery first, before attempting it, start from the steering wheel, then remove the components and label or mark them so you can easily put them back, then go to the radio and use pry bars (plastic preferably) to pry those panels, they rarely use screws to hold them, they use tabs instead, then remove the glove box then the passenger air bags, take your time to find the screws, they are usually hidden from view, or under some panels, the main dash is held by 15 or 16mm nuts.
You will need patience, lots of it, to be able to bring this thing down, common sense is also required a lot, and if you can, do it with somebody, mark and label every nut and bolt and screw and every other thing, so that you will easily figure it out when you assemble it .

You suggest the following:

1. Get help from someone who can disassemble the dashboard BUT fix it myself
---Let me see how far I can with your help over the internet before trying extreme measures like disassembly

2. Fix it myself if I have the tools
---So far I have a multi-meter which am pretty good at using, a test light I have never used, an appetite to learn, and couple of YouTube videos that I have digested

3. Always disconnect the battery first before working on the circuit
---I have always practiced this, I vividly recall destroying a couple of fuses several months ago when I did some work without doing so, so I know this one

4. A work-through for dealing with the dashboard removal
---Let me work you through all I have done so far before confirming that this indeed needs to be done

5. Common-sense and patience, labelling and marking so reassembly will be painless.
---Absolutely lots of this is required plus taking notes along the way so you can undo what you have done should anything go wrong.

Thanks so much for your support

cocoduck:
I suggest you take it to somebody that has the tools to disassemble the dashboard and you do the repairs yourself, or if you have the tools, you can try it your self, disconnect the battery first, before attempting it, start from the steering wheel, then remove the components and label or mark them so you can easily put them back, then go to the radio and use pry bars (plastic preferably) to pry those panels, they rarely use screws to hold them, they use tabs instead, then remove the glove box then the passenger air bags, take your time to find the screws, they are usually hidden from view, or under some panels, the main dash is held by 15 or 16mm nuts.
You will need patience, lots of it, to be able to bring this thing down, common sense is also required a lot, and if you can, do it with somebody, mark and label every nut and bolt and screw and every other thing, so that you will easily figure it out when you assemble it .

Am fighting two codes P1520 and P1512 which could be mechanical or electrical in origin. I suspect that mine is an electrical fault.

It relates to what is called Intake Manifold Runner Control

It is a pretty common problem on Ford and Mazda vehicles that share common engine designs including but not limited to Ford Focus, Ford Mustang on the Ford side and Mazda MPV, Mazda Miata and Mazda 5/6/CX-7

These pictures show how the IMRC looks like!

Both the sealed box and the connector that takes current from the IMRC box to the PCM

Here is a description of the first error code resolution procedure:

DTC Full Name:
DTC 1520 Intake Manifold Runner Control (IMRC) Shutter drive circuit malfunction

DTC Detection Condition:
The PCM monitors the voltages from IMRC control circuit. If the PCM terminal 42 voltage is 3.0V or below unless circuit is grounded during operation, the PCM determines that the IMRC system has a malfunction


POSSIBLE CAUSES:
1. Open circuit in wiring between the main relay terminal D (harness-side) and IMRC actuator terminal 2 (harness-side)


2. Short to ground circuit in wiring between the IMRC actuator terminal 1 (harness-side) and PCM TERMINAL 42 (harness-side)

3. Open circuit in wiring between IMRC actuator terminal 1 (harness-side) and PCM TERMINAL 42 (harness-side)

4. Connector or terminal malfunction

5. IMRC Malfunction

6. PCM malfunction

Here is a description of the second error code resolution procedure:

DTC Full Name:
DTC 1512 Intake Manifold Runner Control (IMRC) Shutter valve close stuck

DTC Detection Condition:
The PCM monitors the voltages of IMRC monitor circuit. If the PCM terminal 3 voltage within 1.6V - 4.9V for 3.15 seconds when the IMRC valve is open, the PCM determines that the IMRC system has a malfunction


POSSIBLE CAUSES:
1.Open circuit in wiring between the main relay terminal D (harness-side) and IMRC actuator terminal 2 (harness-side)

2.Open circuit in wiring between IMRC actuator terminal 1 (harness-side) and PCM TERMINAL 42 (harness-side)

3.Open circuit in wiring between IMRC actuator terminal 3 (harness-side) and BODY GROUND

4.Open circuit in wiring between IMRC actuator terminal 5 (harness-side) and PCM TERMINAL 3 (harness-side)

5.Open circuit in wiring between IMRC actuator terminal 6 (harness-side) and PCM TERMINAL 91 (harness-side)

6.Connector or terminal malfunction

7.IMRC Malfunction

8.PCM malfunction

good if you have an oscilloscope, this would have been a breeze for you, well, since it is a low amperage circuit, use your meter to do a continuity test between those pins and their corresponding pins in the PCM connector, but if were me. I would rig up something to test it using a test light, or if you have a test light that is 200ma or less, it is computer safe.

cocoduck:
good if you have an oscilloscope, this would have been a breeze for you, well, since it is a low amperage circuit, use your meter to do a continuity test between those pins and their corresponding pins in the PCM connector, but if were me. I would rig up something to test it using a test light, or if you have a test light that is 200ma or less, it is computer safe.

Seems to me that an oscilloscope is for big boys, how much does one cost?

I have been using my meter and I will share with you the results to help me zero in on what is going on

I have yet to use a test light, I need to learn how to use one.

basically from the above, the tests required to be done to resolve this issue can be grouped into three:
1. Open circuit tests
2. short circuit tests
3. malfunction tests (connector/IMRC/PCM)

In the next few posts, I will share my findings from conducting the first two sets of tests

There are five open circuit tests:

1. IMRC 1 and PCM 42
-- if faulty can trip on P1512 and P1520

2. IMRC 3 and Body Ground
-- if faulty can trip onP1512

3. IMRC 5 and PCM 3
-- if faulty can trip on P1512

4. IMRC 6 and PCM 91
-- if faulty can trip on P1512

5. IMRC 2 and Main Relay Terminal D
-- if faulty can trip on P1512 and P1520

There are six short circuit tests:

1. IMRC 2 and BODY GROUND
-- This is part of Mazda's recommended IMRC Actuator Inspection, no code specified


2. IMRC 1 and BODY GROUND
-- This is part of Mazda's recommended IMRC Actuator Inspection, no code specified

3. IMRC 1 and POWER SUPPLY
-- This is part of Mazda's recommended IMRC Actuator Inspection, no code specified

4. IMRC 5 and BODY GROUND
-- This is part of Mazda's recommended IMRC Actuator Inspection, no code specified

5. IMRC 5 and POWER SUPPLY
-- This is part of Mazda's recommended IMRC Actuator Inspection, no code specified

6. IMRC 6 and POWER SUPPLY
-- This is part of Mazda's recommended IMRC Actuator Inspection, no code specified

Been away sorting out some financial issues.

So now I got a little time to take this further:

1. IMRC 1 and PCM 42
-- if faulty can trip on P1512 and P1520
RESULTS OF OPEN CIRCUIT TESTS:

Passed

BUT

when I tested PCM 42 with IMRC 3 and IMRC 6, I can observe that there are shorts between the following
IMRC 3 and PCM 42 as well as between
IMRC 6 and PCM 42


2. IMRC 3 and Body Ground
-- if faulty can trip onP1512
RESULTS OF OPEN CIRCUIT TESTS:

Passed



3. IMRC 5 and PCM 3
-- if faulty can trip on P1512
RESULTS OF OPEN CIRCUIT TESTS:

Passed

BUT

when I tested PCM 3 with IMRC 3 and IMRC 6, I can observe that there are shorts between
IMRC 3 and PCM 3 as well as between
IMRC 6 and PCM 3

4. IMRC 6 and PCM 91
-- if faulty can trip on P1512
RESULTS OF OPEN CIRCUIT TESTS:

Passed

BUT

when I tested PCM 91 with IMRC 1, IMRC 2, IMRC 3 and IMRC 5, I can observe that there are shorts between
IMRC 1 and PCM 91 as well as between
IMRC 2 and PCM 91
IMRC 3 and PCM 91
IMRC 5 and PCM 91

5. IMRC 2 and Main Relay Terminal D
-- if faulty can trip on P1512 and P1520

RESULTS OF OPEN CIRCUIT TESTS:

Passed

BUT

Should there be continuity between IMRC 2 and all the 4 pins of the relay?

I ask because there is continuity between
IMRC 2 and Relay terminal D
IMRC 2 and Relay terminal B
IMRC 2 and Relay terminal C
IMRC 2 and Relay terminal A

I think that my problem is as a result of either wires touching other wires or touching grounds that they ought not to, i.e., short circuits and ground faults!

hip hip hip

hurray

I found the short!

details later...

a few wires melted into themselves

failed wires within the wiring harness

bad previous repair job, guess why I am doing it myself? As if I knew!

does anyone know where I can buy the standard non-adhesive tap for repairing wiring harnesses

butt connectors, they don't even sell those in dedicated electronic shops, how sad, they say customers don't ask for those, so they don't sell

all we got in Nigerian auto markets is the adhesive type, and we know what heat does to those.

I'll be done with the job tomorrow.

This is a painstaking job.

I also washed all the wires that got mud on them due to failed insulators, and let them dry before reinstalling the insulators

Thank goodness for the holiday, otherwise, I just would never have started, but I guess I will have to sacrifice another 6 hours to get this done and done well tomorrow

Thanks for all the help everyone

I spent 12 hours tearing apart the wiring harness, checking each wire for shorts

and then zeroing in on the shorts

I also intend to completely replace the insulators

I want to do a job that can last another 5 to 10 years

I saw evidence of a bad repair job, imagine removing the shielding from a failed wire and leaving it totally bare from the firewall to the PCM

nice

"Body ground" is what Kazeem call "ACT".

Body ground is same as Earth. No need to say much, it has been explained above.

Interesting when you get down and dirty.

It always takes longer than you think.

Several wires are shorted, just by the engine and the exhaust very close to the firewall. This is apart from shorted wires at the point firewall itself where the wires both enter/exit the firewall.

Why are some mechanics so wicked or inconsiderate or thoughtless?

There is NO heat shield sleeve on the wiring harness and the wiring harness is resting on the engine and the exhaust.

Why will the wires not burn?

All they used is the adhesive tape and I can deduce that from the tons of adhesive sticking to the wires within the wiring harness. Although all the adhesive tape had long since fallen away.

So I decided to wash the part of the wiring harness taken from behind the engine and the exhaust so that it would be easier to inspect them for damages, and as the water cleared, I saw something interesting. Don't know if this is standard practice, but I am certain before I ever have to start the car, all the water would have dried.

Lots of burnt or on the way to being burnt and discolored wires.

Needless to say a short is a unintended path for current flow. So I can see now why the car computer is confused.

Good that I caught this early, I am safely assume that more wires would eventually get burnt, a fire could be started, and inexplicable trouble codes could come up all because of this.

So far all sections of the wiring harness that checked out have been comprehensively heated shielded, and by the time I am through with this process, every single inch of wire within the wiring harness in the engine compartment will be heat shielded.

Also, the dashboard is down also.

I want to do a thorough job.

I got one of those guys that are familiar with taking my brand of car apart when it is sold to the junk yard to help me dismantle the dashboard.

Am glad I did, we worked together though. I could have done it alone but 1.it would take longer; 2. the job is a bit technical; 3. the service manual says, two people should dismantle the dashboard and 4. I got several bruises from working in the engine compartment without gloves so I am having serious problems removing connectors without assistance

Bravo. A lot of write up. Pictorial representation will do more talk. U kn hw it is... Pics or...

chukel:
Bravo. A lot of write up. Pictorial representation will do more talk. U kn hw it is... Pics or...

Will do.

In other news, no more shorts!

Will start it tomorrow, but everything checks out electronically or electrically using my multimeter

hi, FEGEITOK, I searched online and found this thread. My 2000 Mazda MPV worked well. I replaced the two valve cover gaskets. AFTER THAT I got P1520. I think my harness was not melted like yours but was in a bad condition. When I pull out the valve covers I must have bent the harness and caused the wires shorted. I am wondering how you found the short place. Should I cut off the harness plastic tube and tape and then visually examine each wire inside inch by inch? Thank you.

mfeng:
hi, FEGEITOK, I searched online and found this thread. My 2000 Mazda MPV worked well. I replaced the two valve cover gaskets. AFTER THAT I got P1520. I think my harness was not melted like yours but was in a bad condition. When I pull out the valve covers I must have bent the harness and caused the wires shorted. I am wondering how you found the short place. Should I cut off the harness plastic tube and tape and then visually examine each wire inside inch by inch? Thank you.

Please open it up and check.

In modern vehicles, computers control electrical and mechanical components

Also, electrical components control mechanical components.

That is why, wires and wire harness must be babied. If your mechanic does not do this, it is time to find another.

All the best