PCM not responding

  • 3 POSTS
  • 5.4L
  • V8
  • 130,000 MILES

I just had my car serviced. They replaced the PCM and remote key-less/anti-theft module because my truck was cranking, but would not start. They also programmed two new keys. I was only able to drive it one day and again the same problem, the anti theft light blinks. They sent someone to my home twice to look at it and they cannot figure out the problem. What can it be that causes this again?

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Friday, May 6th, 2016 AT 7:17 PM

1 Reply

  • 29,775 POSTS

What can it be? There are entire books just for diagnosing these types of problems. Your dealer also has access to people at a technical assistance hotline, but using that resource requires the vehicle to be at the dealership and the mechanic will be running back and forth between the phone and your car. There are dozens of things that can cause crank / no-starts, and each of those can have dozens of causes. The frustration of finding the causes is the price we pay for having way too much unnecessary technology shoved into our cars.

The place to start is to determine if spark and / or fuel pressure is missing, then check with a scanner to see if the anti-theft system is causing the no-start. Anti-theft systems are real effective at keeping owners out of their cars. Computer modules are the last things to suspect because they generally cause rather few problems. Stretched and corroded connector terminals, wires rubbed through and grounding out, and intermittently failing sensors are much more common. Door switches have been moved to the latch assemblies where, ... Surprise, ... Water runs down and gets into them.

The fact that you were able to drive your car for a day suggests this is an intermittent problem that happened to be not acting up after the computers were replaced, and that made the mechanic assume he had fixed the problem. Also, do you really think two different computers failed at the same time? Not very likely. Intermittent electrical problems are by far the most difficult and frustrating problems to find. If it acts up again, you know you did not fix it. If it does not act up again, you never know if it is solved or if it is going to let you sit somewhere.

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Friday, May 6th, 2016 AT 7:57 PM

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