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

Tiny
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.
Sunday, June 25th, 2023 AT 9:53 PM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,854 POSTS
These are two different problems.

The code P0300: The P0300 code is a generic diagnostic trouble code (DTC) that indicates a random or multiple cylinder misfire. When this code is triggered, it means that the engine's computer has detected misfires in multiple cylinders, but it cannot determine which specific cylinders are affected.

Misfires can occur for various reasons, including:

Ignition system issues: Faulty spark plugs, ignition coils, or ignition wires can cause misfires.

Fuel system problems: A clogged fuel injector, fuel pressure issues, or a malfunctioning fuel pump can lead to misfires.

Air/fuel mixture imbalance: Problems with the air intake system, such as a vacuum leak or a malfunctioning mass air flow (MAF) sensor, can cause misfires.

Engine mechanical problems: Issues like low compression in one or more cylinders, a leaking head gasket, or worn piston rings can result in misfires.

To diagnose and resolve the P0300 code, you can follow these steps:

Check for other codes: The P0300 code often accompanies specific cylinder misfire codes (P0301, P0302, P0303, etc.). If you find any additional codes, they can help narrow down the issue.

Inspect ignition components: Examine the spark plugs, ignition coils, and ignition wires for signs of damage, wear, or corrosion. Replace any faulty components as needed.

Check the fuel system: Verify that the fuel injectors are clean and functioning properly. Ensure that the fuel pressure is within the manufacturer's specified range. If necessary, clean or replace the injectors and address any fuel delivery issues.

Inspect the air intake system: Check for any vacuum leaks in the intake manifold or vacuum hoses. Test the MAF sensor to ensure it is providing accurate readings.

Perform a compression test: If the above steps do not resolve the issue, it's recommended to perform a compression test to assess the condition of the engine's cylinders. Low compression in any cylinder could indicate a mechanical problem that needs to be addressed.

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. Here's a brief explanation of each code:

C0561 - Electronic Stability Control (ESC) System - This code indicates a problem with the vehicle's electronic stability control system. It typically occurs when there is a malfunction or communication issue with the ABS (Anti-lock Braking System) module, which is responsible for controlling the ESC.

U0140 - Lost Communication with Body Control Module (BCM) - This code indicates a loss of communication between the vehicle's main body control module and another module within the vehicle. The BCM is responsible for various functions such as interior lighting, power windows, and central locking.

U0121 - Lost Communication with Anti-lock Braking System (ABS) - This code indicates a loss of communication between the vehicle's ABS module and another module. The ABS module is responsible for controlling the anti-lock braking system and traction control.

These codes often point to a problem in the wiring harness, connectors, or a malfunctioning module. Here are some general steps to diagnose and address these codes:

Check the connections: Ensure that all electrical connections related to the ABS module and BCM are clean, secure, and free from corrosion. Make sure the wiring harnesses are properly connected.

Inspect the wiring harness: Inspect the wiring harnesses for any signs of damage, such as frayed wires or loose connections. Repair or replace any damaged wiring as necessary.

Scan for additional codes: Perform a comprehensive scan of all the vehicle's modules to check for any additional fault codes that could provide further insight into the issue.

Check the power supply: Verify that the ABS module and BCM are receiving proper power and ground connections. Low voltage or poor grounds can disrupt communication between modules.

Module testing: If the above steps do not resolve the issue, further diagnostic testing of the ABS module, BCM, and other related modules may be necessary.

Check out the images (below). Please let us know how it goes
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Monday, June 26th, 2023 AT 3:36 PM

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