Hi, first post here. 2015 Fit with 78K miles, bought used in 2020. Manual trans.

Short story: My PCM was replaced and now I have CEL, TPMS, Steering and Traction indicators on. OBD2 shows code P0172.

Tuesday: Car doesn't start. I tested the battery and it was good. Starter was replaced at 62K and start/stop button was replaced under warranty extension earlier this summer around 74K. Display showed "CHECK CHARGE SYSTEM," and I ended up having it towed to dealer since they last had the car for start/stop replacement. This exact issue happened to me in May, and the cause was a bad ground from the negative battery terminal to the chassis. I tell the service advisor about this.

Friday: Dealer tells me they saw a code for the PCM and the start/stop button again, oddly enough. I'm very suspicious about the start/stop since it was replaced so recently and the new one has had zero issues (old one was taking several presses before starting). They tell me no worries, both are covered under warranty extension and replace both for me.

Saturday AM: Service advisor says car still won't start after PCM + start/stop replacement. I ask if they checked on the bad ground -- he says there was a miscommunication and technician forgot to check. He calls back and hour later and tells me the ground was indeed the issue. Technician cleaned up the ground terminal and car fired right up. I pick it up and drive it home. Car seemed like it was idling at lower RPMs than usual but was driving very smoothly, so I don't think much of it.

Saturday evening: I run an errand and notice car is idling even lower, around 500 RPM. Before this whole ordeal, it would idle around 8-900. After a few minutes of driving I feel what seems like a misfire (felt like a hiccup as I was putting into first gear) and the dash lights up -- CEL, steering, traction all on, TPMS blinking. I walked to Autozone this morning and bought a cheap OBD2 reader, and it reports P0172. in the 30K miles I've owned the car I've never had any of those indicator lights, aside from TPMS when I had a nail in a tire.

I'm thinking the issue is related to the PCM replacement. Just now I read about the idle learn process after PCM replacement, and I'm thinking since the car didn't start immediately after replacing it, they never did this. I'm not sure if that explains P0172, but it might explain the low idle engine speed, and I feel like they're related.

Either way, I'm bringing it back to the dealer tomorrow. Does anyone have thoughts on this? Does this sound like a shoddy PCM job or something else?

Honestly... really wish I had some tools into the car so I could've cleaned off that ground terminal myself and avoided this ordeal.

 

Brought it back to the dealer today. Said they're replacing fuel injectors, also covered under warranty extension. I brought up the idle learn process and service advisor was confident they did everything necessary after PCM replacement, but I'm still suspicious.

 

Got the car back from the dealer. It's idling at a solid 750 RPMs when warm and it does seem to run more smoothly, which might be attributable to the replaced fuel injectors. I didn't get a straight answer on whether they messed something up with the PCM the first time around, but as long as the car's running well and the dash isn't lit up like Times Square, I'm content.