The Riley Report

• Author: Mike Riley
• Subject Matter: P0880 Code
• Issue: Erratic Shifting

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(Unrelated items could be damaged as a result)

Complaint/Concern:

By the time the owner of a 2011 Chevy Silverado arrived at the shop he had already visited two other repair facilities, but to no avail. According to the owner the truck had been acting erratically for a few weeks. At times, the transmission would delay upshifting and occasionally would have a hard bump or clunk while coming to a stop.

In addition, the diagnostic trouble light would show up until the key was cycled off and back on. Even the trouble light issue was inconsistent. A scanner was attached but initially no codes were recorded.

The truck was taken for a road test and after a short time started to act up just as the owner described. When the trouble light came on a P0880 code was retrieved. At times, the transmission operated quite well.

Cause/Condition:

After further review of the transmission functions, focus was redirected elsewhere. The technician started to rule out items such as loose or corroded wiring as well as any computer issues. During this time the manager happened to ask the owner of the truck if anything had been done recently. As it turned out, the owner, a somewhat-backyard mechanic, had done some maintenance work on the truck. One item stood out as a possible problem, which was the serpentine belt.

Certain aftermarket serpentine belts can create an electrostatic discharge that can impact electrical components that happen to be too close, such as the TCM. In this particular model truck, the TCM is not too far away from the belt, and that was causing the erratic transmission operation and trouble code.

Correction/Modification:

Once it was determined that the serpentine belt was the culprit a new OEM belt was installed, all 11 feet of it, (Figure 1). This issue can occur not only by routine maintenance replacement, but also if certain modifications are made, such as adding an additional alternator.

Unfortunately, even after the belt was replaced the trouble code kept popping up due to the damage inflicted on the TCM, (Figure 2). The shop had no choice but to replace the TCM with a new one. Not only was the TCM replaced, it was relocated to the top of the UBEC cover as well in order to be far away from the belt.

It goes to show: always query customers to find out if any work has been done to a vehicle in for repair.