Codes P0300, C0561-71, U0140-00 and U0121-00, engine running rough?

SCREWLOOSE13

MEMBER
2007 CHEVROLET TAHOE
5.3L
V8
4WD
AUTOMATIC
180,000 MILES

My SUV listed above is running rough and has a p0300 code for random misfire. It has a couple of other codes as well. A c0561-71and u0140-00, u0121-00. I have changed out the spark plugs, spark plug wires, coil packs, new battery, new gas cap. I clear codes after I change part and it starts running a bit rough and smokes a bit out the tail pipe and smells like gas or oil kind of. The Stabil Trak and traction control messages are on the dash. I read those shut off if there is a misfire. I'm thinking possibly to change PCV valve? I'll have to replace the driver side valve cover though. Not sure what to do honestly. Please let me know if there is any advice or if you need more info. Thank you very much for your time.

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
42,973 POSTS

It sounds like you have a MAF sensor that is off or a weak fuel pump. Also, it could be a vacuum leak, here is a guide to help us get started. Use this guide when the engine is cold only:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I would clean the throttle body as well.

https://www.2carpros.com/articles/throttle-actuator-service

Here is how to check the fuel pressure you can rent a gauge at the local auto parts store:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Fuel Pressure (Key ON, Engine OFF) .................... 345-414 kPa (50-60 psi)

Here is a guide to help as well and I have included the MAF sensor replace in the images below:

https://www.2carpros.com/articles/automotive-engine-misfire-code-p0300-causes-and-solutions

Please start a new question for the BCM etc., codes.

The codes C0561, U0140, and U0121 are all related to communication issues between different modules in the vehicle's electronic systems.

C0561 - Electronic Stability Control (ESC) System

U0140 - Lost Communication with Body Control Module (BCM)

U0121 - Lost Communication with Anti-lock Braking System (ABS)

Check out the images (below). Please let us know how it goes

Images (Click to make bigger)