1991 GMC 2500 Pickup Problems

RepairPal has identified the most common problems with the 1991 GMC 2500 Pickup as reported by actual vehicle owners. We'll tell you what the problem is and what it'll take to fix it.

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17
Known Problems

The distributor may develop internal faults. This can cause a rough running engine or stalling condition, the Check Engine Light may or may not illuminate. Our technicians tell us that the distributor should be overhauled or replaced to correct this concern.

On the 4L80-E Transmission (Diesel and 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.

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.

The alternator may fail causing the battery to go dead, or an abnormal noise may develop. The dash warning light may or may not illuminate. A failed alternator will require replacement.

An oil leak may develop from the distributor o-ring seal requiring replacement of the seal.

The air conditioning compressor may develop an abnormal noise and require replacement. We recommend that whenever an AC compressor is being replaced for a noise condition, a filter kit should be installed to prevent any metal particles in the system from damaging the new compressor.

A coolant leak may develop from the water pump. This can result in an engine overheating condition. A leaking water pump will require replacement.

The fuel pump may fail causing the engine to stall and not restart. Our technicians recommend replacing the fuel filter every 30,000 miles to help prevent undue strain on the fuel pump.

The intake manifold gasket may develop and external engine oil or coolant leak. In some cases, an internal coolant leak may occur causing coolant to mix with the engine oil. Running the engine with a coolant/oil mix may result in engine damage. Replacing the intake manifold gasket should correct this issue.

Power brake systems using "hydro-boost" may leak power steering fluid from the hydro-boost unit located behind the brake master cylinder. Replacement of the hydro-boost unit is the common repair to correct this concern.

Our technicians recommend flushing the brake fluid every 60,000 miles.  Brake fluid that is dirty may cause problems in the brake system.

An engine vacuum leak may develop from the throttle body gasket causing a higher than normal idle speed. Failed gaskets should be replaced.

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 anti-lock brake system (ABS) front wheel speed sensors are prone to failure. When a sensor fails, the ABS warning light may illuminate and/or the ABS system may activate erratically.

The power door lock actuators may become slow to operate or stop working completely and require replacement.