In this issue of “Keep Those Trannys Rolling,” we are going to take a look at a 2019 Chevrolet Silverado K2500 that was experiencing a Service 4WD message intermittently being displayed in the Drivers Information Center (DIC).
We first encountered this vehicle when the customer came by the shop because the Service 4WD message would come on and then go right back off while driving. According to the customer, the four-wheel-drive system seemed to be working properly. While the vehicle was with us, we scanned it for codes, and there were several actuator circuit codes set in the Transfer Case Control Module (TCCM). We documented the codes and erased them from the TCCM. We rechecked the TCCM for codes; none had reset.
Initial Vehicle Inspection:
During the write-up process, the customer indicated that the Service 4WD message was continuing to flash at times. The Silverado was equipped with a 6.0L engine, a 6L90E transmission, and an MP1625 transfer case. During the initial inspection, we checked under-hood components such as hoses, belts, wiring, and connections. We checked fluid levels and verified that all fluid levels were filled to the correct levels. We lifted the vehicle up on the rack to inspect the underside of the vehicle and found no concerns there. We connected our scan tool to the DLC and scanned the vehicle for codes. We found codes C0306, C039E & C0396 (range actuator circ) stored in the TCCM, but no other codes were found in any other modules. After completing the inspection, documenting, and clearing the TCCM of codes, it was time to head out for a test drive to see if we could duplicate the Service 4WD message concern.
Test Drive to Duplicate:
We connected the scan tool to the DLC so we could monitor the transfer case system operation. During the test drive, we drove the vehicle through city streets, ranging between 0-45 mph. We drove the vehicle on the freeway at varying speeds up to 65 mph. Everything seemed to be working properly. With the customer’s permission, we drove the vehicle through a couple of off-road trails, where we test four-wheel-drive system operations. We monitored the TCCM PIDs during the four-wheel-drive system operation. The vehicle and four-wheel-drive system seemed to be working properly.
Heading Back to the Shop:
While heading back to the shop, we noticed that the Service 4WD message (figure 1) began to flicker on and off and then eventually stayed on. With the scan tool monitoring the TCCM PIDs during the test drive, we were able to see the range actuator circuit PIDs were erratic while the message flickered. This was an indication that the range actuator or actuator position sensor circuits were having a problem. Once back at the shop, we scanned the vehicle for codes and found C0306, C039E & C0396 (actuator circ) codes had reset in the TCCM. No other codes were present in any other modules.
Taking a Closer Look:
With a technician in the vehicle to monitor the actuator circuits on the scanner, we raised the vehicle up on a rack where we could easily inspect the components of the transfer case control system. We visually inspected the transfer case control system wiring harness for chaffing, rubbing or damage. The harness looked good. We visually inspected the incremental position sensor (IPS), front axle actuator and transfer case motor. The components looked to be in good condition. We performed a wiggle test on each of the component connectors and that’s when we found the problem. During the wiggle test, we notice that the IPS PIDs would become erratic. This was an indication of a connection problem.
Incremental Position Sensor Connector:
The Incremental Position Sensor (IPS) is mounted on the transfer case shift motor. The sensor is a variable position, Hall Effect sensor that creates a signal the TCCM uses to determine the actual range position the motor is moving toward.
The TCCM sends an 8-volt reference signal to the sensor (5-volt on Dodge applications). The sensor indicates the changing position for the transfer case motor in degrees (0.15 increments) of movement. After disconnecting the IPS connector, we inspected the connector for bent, corroded, or oxidized terminals. We found several terminals in the connector severely oxidized, indicating possible moisture or water contamination. We disassembled the connector and found several of the connector seals were missing from the backside of the connector (figure 2). The connector seals are put in place to prevent moisture or contaminants from entering the connector from the harness side of the connector. With several of the connector terminals oxidized and connector seals missing from the connector, our only option was to replace the IPS connector.
Replaced Connector, Repaired Problem:
After locating a new IPS connector, we installed it and rechecked the transfer case control system operation. While monitoring the IPS PIDs, we performed a wiggle test on the IPS harness, and there were no changes to the PIDs. We checked the TCCM for codes and found no codes present. We test drove the vehicle several times after replacing the IPS connector, and the Service 4WD message never came back on. We delivered the vehicle to the customer, and the four-wheel-drive system seems to be working properly.
Connector Concerns:
Missing connector seals have been an ongoing problem on GM vehicles dating back to 2015. It is always recommended to inspect GM connectors for water or contaminant intrusion due to missing connector seals. Replacement connectors are available from:
Well, there you have it, we’ve fixed another one. Sometimes all it takes is a little bit of wiggle and a good connection to “keep those trannys rolling” down the road.
