1991 GMC 3500 Pickup Repair and Maintenance
A guide to problems, costs, maintenance and repair for your 1991 GMC 3500 Pickup
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1991 GMC 3500 Pickup ProblemsService transmission every 30,000 miles
Our technicians highly recommend that the transmission is serviced every 30,000 miles to avoid problems and maintain optimal operating order. As for the 4L80-E Transmission (Diesel adn 7.4L gas engine), Transmission fluid may leak through the electrical connector on the side of the transmission, damaging the wire harness and causing the transmission to shift erratically. Our technicians tell us there are updated shift solenoids, an internal transmission harness, and a connector pigtail available to correct this fault.
One or more heater & AC (HVAC) temperature and/or air delivery mode door actuator may fail, resulting in improper temperature or air delivery. If this occurs, fault code(s) should be stored in the HVAC control module which should assist in diagnoses.
The quick-connect fittings for the heater hoses tend to leak engine coolant. This problem commonly occurs because the metal housing has become brittle, which can break and cause leaks.