Vehicle: 2008 Chevrolet Express Van 1500, AWD, 5.3L, Automatic Transmission/Transaxle

Mileage: 199,585

Problem: The Chevy van would not crank or start, so it was towed to the shop.

Case Details: About a month ago, the shop replaced the under-hood fuse box because of corrosion. The vehicle was fine over the last month or two and then came back with the same problem. There were no diagnostic trouble codes (DTCs). The technician checked various fuses. All the fuses were good. Next, he tested the power mode master (PMM) module circuits; all good there. He also evaluated the ignition switch circuits and the parameter identification data (PID) from the body control module (BCM). Everything looked correct and the powertrain control module (PCM) showed a crank request.

When he used the scan tool to crank the engine over by commanding the crank relay, he got a message on his scan tool saying it was unable due to the immobilizer. It was time to call ALLDATA Tech-Assist.

The Tech-Assist consultant asked the tech if he could communicate with the theft control module. The technician stated he was unable to communicate with that module and a lot of other modules. He also noted that all the modules that were not communicating with the scan tool were on the low speed GMLAN network.

The consultant advised checking resistance on pin 1 to ground of Data Link Connector (DLC) to check the low speed GMLAN Network. It read 21 ohms (good).

Next, the technician was advised to remove the comb from JX200 on the GMLAN network and jump pin A (which is for the DLC) to other pins one at a time and measure the resistance on pin 1 of the DLC. Look for which one reads 21 ohms of resistance. During testing, only when pin A was jumped to pin B in the splice pack JX200. All others showed no continuity. Pin B is for the radio.

The technician decided to remove the radio for bench testing. Once the radio was out, he heard something rattling inside. He turned the radio on its end with the CD player slot facing down and shook it. A coin fell out of the CD Player. He double checked the previous network tests. The short circuit was gone!

Confirmed Repair: The technician plugged the radio back in and reconnected everything. With the coin removed, he had communication on the low speed GMLAN. The engine cranked normally and started right up. The problem was caused by a coin inside the CD player shorting out the Low Speed GMLAN network. Interesting and unusual fix!