P129D and P1682 on a 2020 but runs fine

[Nutro]

I am new to these years and not really sure how to start troubleshooting it. I bought a 2020 and have been driving it for a few days now. I loaded up the kids for their first drive in it and only made it up the hill about 1/2 mile from the house. It was running fine then just BAM, dead, stall. Threw it in neutral and it fired right back up. Drove it back home and checked for codes. Those 2 codes showed up.

I googled and it seem the P1682 is ignition related and the P129D is FPCM but I'm curious why I'd get both of those at the same time. I googled and found some videos and watched one lengthy one. The guy found a chaffed or broken wire in the harness going to the FPCM but I was just digging around under the truck and I don't SEE anything from just visually looking and feeling around.

This is a PPV and has 2 batteries in it. They are both non-branded it seems. They both have a "window" on the top of the battery and I can see "green" inside the window. I am not sure when they were replaced.

Since this is a 2020 and it has the battery isolating relay, if the aux battery was bad or going bad, would it still kill the main battery on the pass side?

 

[Nutro]

I installed a new battery on the pass side and the P129D is gone, for now. The P1682 is still there but when I google it, it seems that everyone with that code has a no start issue. Mine fires right up and runs well.

 

[Nutro]

Nobody has had this code before? I figured I'd get better answers here than Facebook groups haha

 

[Fless]

From what I read the P129D code indicates low ignition voltage at the FPCM, or on that circuit. Is your code a History code or a Current code? Has the connector at the FPCM been tested for powers and grounds?

If it's not a current code, perhaps the new battery fixed that.

 

[Joseph Garcia]

If you don't already have one, I recommend that you get yourself a quality bi-directional scanner to add to your tool box. Then, you will be able to read ALL trouble codes, along with a brief explanation/pointer to the source of your issue. You will also be able to reset/delete trouble codes, after taking corrective action. You will literally save thousands of dollars in diagnostic and repair costs over the life of your truck, and you will most likely recoup the cost of the scanner within 1 year.

A quality bi-directional scanner will help you drill down to root cause of your P129D code.

 

[Nutro]

From what I read the P129D code indicates low ignition voltage at the FPCM, or on that circuit. Is your code a History code or a Current code? Has the connector at the FPCM been tested for powers and grounds?

If it's not a current code, perhaps the new battery fixed that.

After I installed the new battery, the P129D went away. I plugged in and deleted the P1682 but it came right back so it I think its a stored code.