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6 COIL DRIVER CIRCUIT 2002 Jeep Liberty V6

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15K views 12 replies 3 participants last post by  Frango100 
#1 ·
engine light on code P0356 Cylinder 6 ignition primary circuit
Touble shooted. COIL DRIVER CIRCUIT has power when engine not cranked. no power when engine cranks or runs. Doing opposite of what it is supposed to do. I disconnected the PCM but coil 6 - driver circuit has power.

Surely no issues with the PCM. Looks like the primary circuit is either not connected to PCM or shorted to some hot wire.
 
#2 ·
Welcome to the garage.
That is strange. Not familiar with the V6, but normally all coils are power fed via the ASD relay.
Did this suddenly happen, or did you buy the jeep like this?
 
#3 ·
Welcome to the garage!

I'd look into a shorted wire somewhere in the ignition harness. Then move to replace the asd relay as it could be internally shorted
 
#5 ·
The ASD relay feeds all the coils, so a problem with the relay will influence all coils.
Also the PCM will only switch the ground from the coils, not the power. Disconnecting the PCM should not do anything to the power (besides its the PCM that switches the ground for the ASD relay as well)
Did you check the wiring, because it almost looks like that someone messed with it.
 
#8 ·
Do you have a schematic diagram of the ignition system? Normally all the coils are fed via the ASD relay via the same wire. At some point, at a stud, separate wires should go to each coil.
If #6 is not following the rest, then the power wire must be connected to something else.
 
#11 ·
1. With PCM connector disconnected checked the PMC C1 - 5 . It is measuring high voltage. That explains why the driver circuit has poser when engine not cranked. All the time except when engine is cranked.


2. Also checked the continuity from coil connector to the PCM connector.

PCM connector pin for C1-5 ligt comes on the tester when the coil connector is connected to the coil 6. All other coils have been verified to their respective PCM connector pins.

3. Conclusion - PCM is sending power to the coil 6 drriver circuit when not supposed to and NOT sending power when required - (engine is on).

4. If I replace the PCM would it fix the problem. What might have caused this. My jeep has 160K. This happened at least 3 years ago when the mileage was about 157K. I have been driving very little for the past 3 years.

Appreciate your thoughts.

Thanks
 
#12 ·
Frango100

No I do not have wiring diagram.

The diagram I have from internet does not show - what you described.
This diagram I have is simple and shows that the coil driver wire connects directly from the plug to the PCM connector. Does not show any other sensor or connector in-between.

Connection from coil 6 to the PCM connector is continuous with PCM connector disconnected from PCM. tester light comes on at C1-5 of the PCM connector.

I noticed in the harness - all the wires from left side (cylinders 2, 4, 6) seem to go in one direction - just as you described.
 
#13 · (Edited)
As said before, I don´t know the Liberty V6, but in general, the PCM only supplies the ground for the ignition coils. It has a separate driver for each coil and makes and breaks the ground as demanded by the programming and sensor inputs.
There can be a problem with the ignition coil driver #6, but you still should have 12V at the other side of the coil, coming from the ASD relay.
So where did you measure the voltage on? Is it the 12V supply coming from the ASD relay, or do you measure after the coil ( so in fact, the wiring in between the coil and the PCM?
In the last case, I would expect a problem with the coil driver in the PCM. If it will keep the coil connected to ground all the time, then the voltage will be 0.
 
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