2015 GMC Sierra Misfire with Traction Light

Gurprit Dhaliwal · March 20

Hello team, new to the forum and new to the GM truck world.

Issue: truck seems to be misfiring under heavy load. The engine light will begin to flash and traction light comes on. After a minute or so, traction light will go off but engine light will remain. Codes cleared and drives fine until another misfire. No issues while truck starts.

I’ve replaced the coils, wires and spark plugs. Cleaned up 4 grounds (ECM, and the 3 under the truck on the driver side).

I’ve attached the codes present. P300 and rest all U codes. I’m at loss. If there is anyone experienced this please help! Next step is the stealership.

link to video.

CamGTP · March 20

That scan tool should allow you to watch each cylinder for misfires with the graphs. You can then get it to misfire and look to see what cylinders are doing it. Then figure out a repair from there.

If the issue isn't spark related, then it's going to fuel related or mechanical with possible lifter, valve springs etc etc. Fuel injector failure is common on these trucks.

Gurprit Dhaliwal · March 20

Thank you Cam. I will check the cylinders. Will report back with findings.

rlcole321 · March 23

Does any of the U codes come back when you clear them?, how long have you own the truck?, has the engine compartment possibly been pressure washed? You may want to pull the connectors one at a time off the ECM and check for possible corrosion.