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PCM ground issue, will not start?

Tiny
BOWTOMECHA
  • MEMBER
  • 2008 FORD EXPLORER SPORT TRAC
  • 4.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
As in there's no starter sound. The starter is brand new and gets power, and park/neutral switch tested fine. The fuses all look good. The relay works.

There is no communication with the PCM through obd2. Also, the PCM port for the starter relay doesn’t read anything. I’ve narrowed it down to the PCM ground at the fuse box at the very least. I’m trying to test the wire harness on the PCM end and the different grounds and ports involved. I’m looking for a diagram or pin out for the PCM. It says HCZ1on it which corresponds to the 12A650 model. I saw somebody else sharing diagrams for an older explorer in a thread about the 12A651 I think and I’m wondering if they are the same layout for the various explorer and sports trac styles.

Thank you.
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Wednesday, September 25th, 2024 AT 2:51 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

I attached the pin-outs for all connectors at the powertrain control module. Note that the first connector does contain the starter motor control circuit. Additionally, the legend for each connector is included.

Take a look through them and let me know if it helps or if I can help in any way.

Take care,

Joe

See pics below.
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Thursday, September 26th, 2024 AT 1:27 PM
Tiny
BOWTOMECHA
  • MEMBER
  • 5 POSTS
Thank you for this. I’m trying to test the pcm ground port where the relay is. What pin does it lead to on the harness? Or does it go to another relay first?
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Tuesday, October 1st, 2024 AT 1:04 PM
Tiny
BOWTOMECHA
  • MEMBER
  • 5 POSTS
Pin 2 goes to the pcm ground at the starter relay? I’m trying to test continuity between the ends to rule out the harness.
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Tuesday, October 1st, 2024 AT 1:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

I'm not sure if you are referring to the relay or the PCM. I attached the wiring schematic below for the starter circuit. Take a look and let me know if that helps.

Note: Power from the ignition switch (start position) runs through the neutral safety switch, through the primary side of the starter relay, and gets ground a ground signal from the PCM. Once that happens, the secondary side of the relay is closed and power from a 30-amp fuse (fuse 11) sends power to the trigger wire on the starter motor.

Joe

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Tuesday, October 1st, 2024 AT 7:46 PM
Tiny
BOWTOMECHA
  • MEMBER
  • 5 POSTS
Yes, I am troubleshooting the PCM ground that goes to that starter relay. It doesn’t seem to work so I’m trying to test continuity from that port to whatever pin it corresponds to on the PCM harness to make sure the wire is okay. I also can’t get a reader to communicate with the PCM so I’m trying to test the grounds and power. The fuses seem to be fine so far although I might have overlooked one somewhere. After this, I guess I should test any sensors voltage to make sure they are okay? I read that a bad sensor can do this to a PCM somewhere.
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Wednesday, October 2nd, 2024 AT 11:11 AM
Tiny
BOWTOMECHA
  • MEMBER
  • 5 POSTS
I guess I should add that the starter was replaced with a new starter after this problem began, bridging the ports on the starter relay location doesn’t make the starter turn, the neutral safety switch tests okay, and when the issue happened it was a pretty hot day and the truck was parked on an incline.
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Wednesday, October 2nd, 2024 AT 11:18 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

If you are getting power to the relay and the starter still doesn't engage when you jump the relay, either the trigger wire at the starter is open or you got a bad starter.

Let me know your thoughts.

Joe
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Thursday, October 3rd, 2024 AT 6:30 PM

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