SureTrack Real Fix: Expecting High Volts

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SureTrack Real Fix, ProDemand, 1999 GMC Suburban

Real Fixes from SureTrack® provides expert-based knowledge captured from millions of documented repairs and community discussions. Read on to see how SureTrack can help you fix tricky issues that, like this 1999 GMC Suburban, are not easily diagnosed with OEM information alone. SureTrack is available at no additional cost within ProDemand.

This fix illustrates the power of the SureTrack community to quickly help a fellow tech solve a tricky diagnosis. SureTrack community member, tanua_ext10, had a 1999 GMC Suburban stuck in 4×4 high, roll into the shop. They posed the question to the community, and with the help of Ericsautomotive and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

Vehicle
1999 GMC Suburban K1500 5.7L Eng VIN R

Title
4×4 Doesn’t Engage

Complaint
The vehicle was stuck in 4×4 high

Diagnostic Steps Performed/Parts Replaced

Encoder circuit codes were shown during the original scan, but c0327 currently appears. Replaced old transfer case with used/good transfer case due to a leak and inability to check fluid levels from the damaged fill plug and the gear selector turned very hard. After transfer case replacement and a new encoder motor, c0327 comes up and is stuck in neutral.

Removed the encoder motor and shifted the transfer case in 2wd. When selecting the 4×4 switch, 2wd or auto, or 4wd high, nothing happens. Both 4×4 fuses are good and the 20 amp one blew a few times but now isn’t blowing the fuse.

On the 4-wire plug in the encoder motor, I found ground on the tan wire and 12 volts of power on the orange that feeds back to the 20-amp fuse. We tried 2 used tccm modules and when plugged into our Snap-on Zeus diagnostic scan tool, the info says invalid.

Cause
The system will try to turn the lock solenoid off by opening the ground circuit. If the module is unable to de-energize the solenoid, the system will not attempt to de-energize the solenoid again during that ignition cycle. Auto transfer case lock output will read back as a low voltage when a high voltage is expected. These are the conditions for setting the DTC c0323.

Correction
After looking at the wiring diagram and understanding what was ground and what should have power voltage going to it and a test for c0323, I found a short or open circuit on the E1 tan wire feeding from the encoder connector to the tccm module. Fixed the broken E1 wire, which was corroded, and 4×4 works properly.

SureTrack® adds to the power of ProDemand® with an exclusive combination of real-world knowledge and powerful diagnostic tools, all wrapped in an interactive community of professional technicians. Designed to help automotive shops increase accuracy and efficiency from diagnosis to completed repair, the industry’s most comprehensive repair information resource is just a few clicks away.

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About the Author

Abagail Lucero

Abagail Lucero is the Product Marketing Manager for ProDemand. She joined the company in 2011 as a member of the SocialCRM shop marketing team and has served in many roles at Mitchell1, lastly as Security and Compliance Supervisor. Abagail holds a Bachelor of Science degree from California University of Pennsylvania.