Question: P2302 --ignition failure coil A--secondary circuit -- replaced PCM and coil. Resistance is 0 on
negative pulse wire from PCM to coil. Car runs. . but poorly. What else to do.
Mechanic: Make, model, engine size please?
Dodge, 2005 Grand Caravan, 3.8L.
Is the resistance 0 ohms or open?
I got 0 ohms on all 3 negative pulse wire from PCM. And when I backprobe at PCM I get pulse 2 wires during
crank and run state. But the wire feeding coil A has no pulse.
Hmm. Not really sure, don't have much experience with particular vehicle electrical systems operation.
If there is no pulse with test light on backprobe at PCM, does it make any sense to run a new wire from PCM to
coil? If so, how does one do that? What is needed to get wire inserted into the pin positions?
No. The PCM is what sends the pulse.
Theory from a different mechanic was also that I might have a short to ground of some kind in the harness that
was causing PCM to not send negative pulse on the wire to Coil A. Seems really, really odd that replacement
PCM would have same problem on exactly the same wire.
If shorted, you can check that by doing resistance check from wire to a good ground. But it must be
disconnected from coil and PCM. Yes, i would not think same problem with another PCM.
But I did the resistance check with disconnection from coil and PCM. That is when I determined, checking each
wire at least twice, that resistance is 0. That indicates that there is not short to power or ground also? I don't
No, that just indicates the wires is not broken from end to end.
Do you think it's a possibility that there could still be a short somewhere in harness that is causing PCM to not
Yes. The wire could be shorted to ground or another wire inside the harness.
Any suggested links to electrical tutorials on how to do that? Or on properly replacing negative pulse wire to the
connectors? You could recommend slicing open the harness to try to get wires apart to see where the short
might be? Or is it hopeless with more tools than a test light and very basic meter?
First check resistance to ground. Should be 0 ohms. If O, then it is not shorted to ground, but that does not test
for short to another wire. You would have to open harness and follow wire to check that. You could always just
cut wire at each end and crimp on a new one from PCM to coil.
Ah. I suppose parts store could have stuff for splice. I don't have it on hand. I'm inclined to that at this point. Do
you think a short on some other wire in the harness might be causing issue of no actual pulse coming from
Yes, it could. But it could also cause a problem on the circuit of the wire it may be shorted to.
I appreciate the pointers. I'll try to get you a donation. I see its done via Paypal.
Thank you and good luck.
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