[Jlowery117]

I recently replaced the shift harness for my 2018 Malibu because of the shift to park message. Unfortunately my battery was drained also so I replaced that as well with an AGM battery. The shift to park error is fixed but now I'm having issues with the TCM. The check engine light is on and the main code I am getting is P0700, but several other codes as well all mainly dealing with low voltage. Code P-305e, P-3051, P-3055, P-3056 all dealing with dc/dc converter. When I crank then car and put it in any gear that gear indicator in the dash blinks. Also when I put it in reverse the back up camera does not come on. My driver side break light, and passenger side headlamp stopped working also. Changed bulbs but the bulbs where fine. The Parking lights still work on those side but not the Break or headlights. Please help car ran fine before the shift to park error but now I'm having all kinds of electrical issues. I have checked all the fuses but not relays.

 

[repairman54]

Looks like the DC to DC convertor is bad. If you search your codes and the convertor those codes come up for it being bad. Check it's connections and unplug / plug the connectors. If that corrects it then is was a poor connection in the connectors.
That convertor also links to the TCM to determine what gear the transmission it in to activate auto stop as that convertor is used for the auto stop function.

 

[Jlowery117]

I have a 2018 Malibu and my right (passenger) headlight and my left break light stop working. I replaced the bulbs but the bulbs are not the problem. The parking lamps still work and the reverse light still work but the break/tail light and head light still not working. Would this be caused by a bad BCM? The car sat for 2 weeks with a dead battery because of the shift to park issue. I replaced the shifter and battery and the day after is when the lights stopped working.

 

[JTR19]

A BCM failure would not result in one head light and one tail light going out. If it were a BCM issue then both head lights and/or both tail lights would be out.

 

[DrivenDaily]

You have one or more of the following to find and fix:

• Bulb
• Socket
• Wiring
• Fuse
• Relay
• Terminal connector (plug)

 

[Jlowery117]

I recently replaced my shifter and battery because of the "shift to park" issue. My car sat for about 2 weeks dead so after I replaced the battery I also had to replace the DC/DC converter. After replacing the battery my lights were working fine. I think messed up but probing with the fuse checker, but my passenger side head light and driver side brake brake light stopped working the next day. I replaced and new bulbs still did not work (nothing was wrong with old bulbs). What could be causing this issue? Could it be the BCM? I don't see any blown fuses.

 

[DrivenDaily]

"Probing with the fuse checker" while the BCM was plugged in just might have done something bad. If you probed a GM LAN (computer data line), then the communication system could have been damaged.

However, your lights are on a single circuit, so when the BCM tells the headlights to turn on, it tells "them" to turn on, not just one. If one turns on, the other should as well, and it won't have anything to do with probing.