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2002 Jeep Grand Cherokee - Won't crank sometimes

My wife’s Jeep will randomly not crank. when I try to test the starter wiring etc. it will decide to start or will be too hot to reach the starter wiring to test it. I have replaced the starter 3 times now to no avail. Sometimes if I hold the key in the crank position and I step on the brake pedal it will start cranking. I have checked all of the wiring to the starter all connections at the transmission, crank sensor, ecm/bcm, and randomly all of the other sensors. I have disconnected and cleaned every ground connection I could find even under the dash. have tried both key thinking there may be an anti theft issue replaced the battery and terminal ends and the problem persist. I spent 30 years as an ASE certified master tech before moving on to something less complicated and stress free (brain surgery) and I’m at the end of my rope. We have full coverage insurance. Any suggestions?

How many miles? Maybe the engine is getting tired on this 19 year old vehicule.

My son’s 98 Wrangler had a no crank problem. Hot wiring to the starter made it crank. Turns out the fuse box had corrosion and the crimped connector for the starter relay came apart. Impossible to get inside the box to re solder/reconnect. Also happened to the light switch. I ended up wiring around the box -added inline fuses. PITA but can be done.

it’s still young. it only has 125k on it and I don’t think a worn out engine will cause it not to crank.

Have you tried shifting the transmission into neutral before attempting to start it?

Tester

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Sadly I can’t get it to not crank long enough to check out the problems in a normal way so I have pulled the starter relay and others to check for corrosion and wear/heat issues with no problems found. Terminal are good and tight with no corrosion.

Yes but as soon as I step on the brake pedal it will start cranking, don’t have to shift it. Spent a couple of hours under the dash checking connections and looms and found nothing out of the ordinary.

A wiring diagram might be useful. I can imagine the system having both a clutch and a brake interlock, so that at least one must be activated for the starter to work.

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Auto trans no clutch. Examining the wiring diagram I could find no connection of the brake interlock to the cranking system brake interlock only affects the shift lever. I’m beginning to suspect the PCM may be getting a little wonky.

I do not have a wiring schematic for you vehicle so I’m guessing here a bit. The diagram I looked at (and I never fully trust any of them) shows that power should be present at terminal 86 of the starter relay all the time.

Terminal 85 of the starter relay goes to the PCM, the transmission control solenoid, and the neutral safety switch. That brown/yellow wire shows to be grounded in all 3 and is wired in parallel.
Might need to revisit the neutral safety switch part of this. Locate the brown/yellow at the neutral switch, ground it with a jumper, and see what happens. If it cranks, time for a neutral switch.