PCM pin 31 supplies ground to relay pin 85, and the ignition switch supplies power to pin 85 of that relay. So superficially, if relay pin 85 doesn't have ground with the key at start, that would mean either the PCM or the park/neutral switch is bad, or there is a related wiring/connector issue. And, by the same reasoning, if pin 86 doesn't have power with the key at start, that would indicate the ignition switch or related switch wiring is bad.

However, there is one other thing that you need to be aware of. The IPM (fuse box +FCM) is a notorious culprit for MANY different electrical issues on these vans. The IPM construction allows moisture in, which causes corrosion to build up on the electrical components. I had a permanent jumper wire to bypass the IPM horn circuit on my van, and many others have reported all sorts of weird electrical issues that were ultimately resolved by bypassing the IPM in some cases, or replacing it in others. So all of this means that ANY circuit passing through the IPM is a potential failure candidate.

I would start by checking relay pin 86 for power, and pin 85 for ground with the key at start, and it would be expected that one of those two will be missing in action. At that point it's important to determine that the IPM is either innocent or guilty. You can do this by going to the source (the ignition switch or pin 31 of the the PCM connector), and testing to see if the missing signal shows up there. If it does, the IPM is the issue. If not, then either the ignition switch is bad (an easy fix), or the PCM isn't supplying ground (which is definitely the least desirable outcome you would prefer to see).

 

 

Front control module provides power, routed through the IPM to pin 86 whenever the key is turned to START. The front control module gets a bussed signal, if I'm not mistaken, from the PCM reading the ignition switch position.

Pin 30 should be live at all times, key off or on. It is battery fed


Pin 85 From the PCM, should provide ground when the key is turned to START position. This will let power flow from pin 86 to energize the windings, creating a magnetic field to pull in the "switch" connecting 30 and 87 to send power to the starter solenoid. A weak PCM ground can make pin 85 a weak ground source, causing the starter to "bounce", mimicking a low battery output.


Turn the IPM over and check for corrosion in the terminals. I don't see it much here, but up north it's very common.


I included a pic of a wiring harness that was soaked with battery acid. I'm sure it took some time for this to happen. But I see this quite a bit. The second pic is with the battery tray out and I've cleaned everything getting ready to splice wires. Pay particular attention that ground in the middle of the second pic. That is a body ground right under the battery tray. That little ground and the one on the lower front under the headlamp are the two most troublesome on these minivans.