Help with some codes...2017 Buick Regal GS

[johnh]

Car shudders under load. Can rev in park to 3000-4000 rpms nice and smooth. Stock Calibration, never flashed.

Underload it stutters, then throws the following codes:
U0401 Invalid Data from ECM
U0100 lost communiction with ECM
P0300 Random Misfire.
U0401-codes.jpg

Only oddity I saw in the log was the Vehicle Speed (SAE, logged) didn't match actual vehicle speed (log showed max 6 mph and we were easily at 40 mph)
Voltage on Control Module and battery are good.

What would cause U0401? Its a new one to me.

[TheMechanic]

Don't worry about your "U" codes right now. They are history codes anyways. Issue may or may not come back. You need to focus on the P0300 engine misfire(s). Check your freeze frame data so you can determine the cylinder and at what load/rpm the misfires are occurring. That will give you a path towards a diagnosis. Secondary ignition issues are likely. Then fuel issues.

[johnh]

Ok thanks. The U codes are recurring, meaning we clear them and they come right back.
We had a code for misfire on Cylinder 3. Changed the plug and installed a new coil pack... the Cylinder 3 code went away. But still the generic P0300 code persists. Need to take more scans.

[TheMechanic]

P0300 is a permanent code. It needs to run the self diag. Make sure to visually check current AND history misfires in your data stream to verify you don't have misfires. Big cams down low can cause them. That's why it is customary to set the misfires to 32K in those areas. I don't disable misfires completely as I want to know if I have a misfire up top. It can give a good freeze frame for fueling and or secondary ignition issues. Obviously not in your case because it is stock.

[gtstorey]

I would check for corrosion on the various module connectors if the comm codes are recurring, followed by a wiring harness inspection.

Actually, this isn't true. I would start with reading the diagnostic steps for those codes in the service manual.

[tunerpro]

Also, make sure you don't have a broken piston. These engines are notorious for breaking pistons (tuned, or not), with cylinder 3 being one of the most common failures. Pull your oil cap off while the engine is idling and see if you get rhythmic puffs out the crankcase. If you do, you have a broken piston. You can also do a compression test on the engine.

The factory service bulletins identify a persistent P0300 and rough running engine as a suspected broken piston, which is why I mention this.

[johnh]

Thanks everyone!

Replaced all the coil packs with higher quality ones (MSD). Seems to have fixed the problem so far, runs fine, no codes. Don't use cheap coil packs and replace any old ones when you do others.

Yeah I saw the broken piston TSB...that was scary... my son (its his car) didn't want to pay for that...

And those plugs were pretty black and sooty for stock tune...but I don't have much experience with these turbo 4 engines...

[gtstorey]

Don't know how the coils would have anything to do with the recurring "U" codes. I guess maybe they could put off enough HF noise to interfere with the communication network, but I think that would screw up the radio first.

[johnh]

Don't know how the coils would have anything to do with the recurring "U" codes. I guess maybe they could put off enough HF noise to interfere with the communication network, but I think that would screw up the radio first.

Me either, but since all the Coil Packs have been replaced, no codes, no issues.