A frustrating series of intermittent electrical issues plagued my vehicle, starting with a track event on March 6th. While performing well, the transmission exhibited harsh shifting. Although no Check Engine Light (CEL) or Diagnostic Trouble Codes (DTCs) appeared initially, this marked the beginning of a cascade of problems.
The Onset of Communication Breakdown
On March 11th, after a 300-mile trip, a CEL illuminated upon refueling. Clearing the codes revealed a concerning pattern: communication errors dominated the DTCs. These pointed to a potential issue with the Control Module Power Circuit, as various modules like the Transmission Control Module (TCM), Body Control Module (BCM), and Engine Control Module (ECM) reported lost communication (U0073, U0100, U0121, U0140). Additionally, a B1325 code indicated low voltage in a control module power circuit, further strengthening this suspicion.
Escalation and a Tow
The situation worsened on March 19th. En route to another track event, the CEL reappeared, accompanied by the transmission locking in a single gear. The DTCs mirrored the previous communication errors but now included U042B, suggesting invalid data from the chassis control module. OnStar directed a tow to the nearest dealership.
Temporary Respite and Recurring Problems
Clearing the codes allowed for a short 10-mile drive before another CEL triggered. This time, only two codes appeared: P015D, indicating a faulty oxygen sensor (HO2S) on Bank 2. Opting for professional diagnosis, the vehicle was taken to the dealership. They replaced the O2 sensor, seemingly resolving the issue. However, after a successful track session on April 2nd, the CEL returned with P0196 (engine oil temperature sensor performance) and the recurring U0140 communication error with the BCM.
Suspicion of a Deeper Issue
The intermittent nature of the problems, coupled with the variety of affected modules and the initial low voltage code (B1325), leads to a strong suspicion of a problem within the control module power circuit. Faulty wiring, a failing power supply, or even a problematic ground connection could be the root cause, triggering seemingly unrelated sensor errors. The dealership’s approach of addressing individual sensor codes without investigating the underlying communication issues is concerning. A thorough diagnostic process is crucial to identify and rectify the true source of the malfunction.
Seeking a Resolution
The next step involves a more assertive conversation with the dealership, emphasizing the need for in-depth diagnostics focused on the potential control module power circuit issues. A comprehensive electrical system check, including wiring harnesses, grounds, and power distribution, is necessary. Resolving this intermittent problem requires moving beyond symptom-based repairs and addressing the underlying cause.
Conclusion: The Importance of Thorough Diagnostics
This experience highlights the importance of thorough diagnostics when dealing with intermittent car problems. While replacing faulty sensors might temporarily alleviate symptoms, addressing the root cause, especially in complex electrical systems involving the control module power circuit, is crucial for a long-term solution. Hopefully, a more focused diagnostic approach will finally pinpoint and resolve the underlying issue plaguing this vehicle.
