1999 GMC Sierra 2500 Consumer Review: Service 4WD Light

1999 GMC Sierra 2500 - Consumer Review

Average Consumer Rating

2 Total Reviews

SLT Extended Cab Pickup (5.3L V8 4-speed Automatic)

Build Quality
Reliability Value
Service 4WD Light
By cw4915e on


1999 GMC Sierra 2500 SLT 3dr Extended Cab SB


4WD light comes on intermittently lately. Poor troubleshooting procedures from a Chilton manual led me to replace the front diff actuator motor. Seems the real culprit is a sticky selector switch. Humidity may be affecting this switch, apparently the resistors are shot for each position and loses ability to keep voltage signal to transfer case module. Original battery lasted 6 years so that was awesome to get over 6 years from a battery. Also developed a leak at the front differential. First thought it was the output seal but ended up being the plastic vent cap that screws into the diff.

Best Features

4 wheel disc brakes, 6.0L engine, tow/haul feature, large console, overhead console, more room in extended cab with new body style 3rd door

Worst Features

More durable 4WD switch, better vent design for front diff,
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