Starter relay PCM ground
155

Asked by Jeffrey Feb 27, 2017 at 05:13 AM about the 2008 Ford F-150 Lariat SuperCrew 4WD

Question type: Maintenance & Repair

2008 Ford F150 with approximately 150k miles. The truck doesn't start because of a bad ground on terminal 85 of the starter relay. I'm assuming the PCM is not allowing terminal 85 on the starter relay to ground for whatever reason.
Could this be a bad PCM? Is there something temperature-wise that is involved? When I use a wire to ground terminal 85 on some metal near the glovebox the truck starts right up but after it runs for awhile it won't start again. But if I turned it off before it warms up it will start again. This is why I'm thinking temperature is involved. Any ideas? Thoughts?

3 Answers
10

Brandon answered 5 years ago

Jeff how did you confirm the faulty PCM? I'm experiencing a very similar issues, but with the additional facet of melting the OTIS diode in the aux relay box.

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10

Guru9HB3NQ answered 3 years ago

2008 f150, same issue, all circuits are good. the pcm won't ground the starter relay. I can remove the battery terminal and get one start then no crank no start. I am wondering what conditions would cause the pcm to not provide ground? I am considering cutting the wire between the relay and pcm (LG-VT) and grounding the relay sid while leaving the pcm side open. I know this works but its not perfect.

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