2016 CHEV MALIBU cruise control

Complaint was "cruise control shuts off on its own" and "instrument cluster sometimes drops out" and "stability light comes on" The most evident of these is cruise drops out on its own. There was loss of communication codes, cluster/bcm to pcm etc. The reasons that cruise dropped out according to the reasons given in the PCM were, Cruise switch canceled, brake pedal applied, incorrect gear ratio.... none of those was real, the pcm was throwing out those as the reasons why it canceled the cruise.

Cruise switches are hardwired to the BCM and the BCM then transmits cruise requirements to pcm via data bus. With enough driving it was noted the cruise would barely drop out on its own when it was set at 40-50km/h but much more prevalent at 80km/h+. So first picture is good high speed CAN using GM's data bus diagnostic tool, second picture is good medium speed CAN, third picture is High speed CAN the instant the cruise kicked out. With that knowledge we had to decide what the issue is, see 4th picture, with available modules on high speed CAN. By unplugging X1 on telematics control module after the car was started, (key functions with BCM) we eliminated the whole right half of the BUS, we were able to drive the car and watch the data bus tool for the problem (but we couldn’t use the cruise on this test drive cause the cruise originates in the BCM) the problem was still present.

Now it was much harder to isolate because unplugging any of the remaining modules posed a considerable problem for test drive. So we did our best in the bay with watching the data bus tool, we were very close to condemning the ABS module. The problem was seemingly gone when it was unplugged. But with a little more harness manipulation it was confirmed that was not the case. Eventually it was confirmed there was Pin head size rub through on the CAN low (Pin 14) white wire where the red arrow is pointing in the picture. That is where the wiring harness passes over the battery tray.

As the car was going down the road... with just enough wind pressure there was more torque on the engine, this flexed the engine mounts a little bit more than when the car was going at a lower speed, less wind resistance, not as much flex. But at the higher speed with the torque that white wire would just ground out a little on the battery tray and cause the communication glitch which the pcm conveniently decoded as a brake input, or incorrect gear from the trans etc. So once the problem was located it probably took about 10 or 15 min with a dab of liquid electrical tape and a zip tie or two to fix. There was likely around 7 hours put into this diagnosis/repair.

So to help out the group.... (I don’t know what the client paid) from my vantage point this would be a $2000.00 repair. Early on in this information gathering before we actually saw the glitch in the buss lines we decided to update the software in the BCM and the PCM as they both had updates, we had nothing to loose by doing it but it did not take care of our immediate issue.

Stronger Together

Every year new vehicles are becoming more advanced with valuable features that keep us safer and more comfortable. From collision avoidance systems to lane departure technology, cars are now sophisticated computer programs running on four wheels. Maintaining these high-tech vehicles is also becoming more sophisticated, and specialized knowledge and equipment are now critical to keep your car on the road.

Acquiring knowledge and managing the cost of specializing in these electronic systems and software for all vehicles is becoming extremely hard for an independent shop That is why we have joined an automotive network called Elunity. Elunity is a network of local independent automotive shops that are dedicated to learning, collaborating and growing together. Through this network, we can continue to provide complete auto service by having access to original manufacturers’ information, software and electronic tools.

We are excited to build an advantage in solving the complex and ever-evolving automotive repair challenges.