Top 5 GMC Sierra Problems: 1st Generation (1999 to 2006)

The GMC Sierra 1500 is a popular pickup truck that branched from the C/K model line for the 1999 model year with its sister the Chevy Silverado. This post reviews the top 5 GMC Sierra problems owners have encountered with the first generation, years 1999 to 2006.

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Top 5 Issues with the 1st Gen GMC Sierra 1500 (1999 to 2006)

1. Headlight Switch Failure

Symptoms of Headlight Switch Failure

  • Headlights won’t work at the set settings

Causes of Headlight Switch Failure

The bulb may have burned out or the fuse might be broken but it’s likely the headlight switch is causing these problems on the 1st gen Sierra.

How to Fix Headlight Switch Failure

Double check the headlight bulbs and headlight fuses. If the headlight switch needs to be replaced, the replacement steps include removing the trim, disconnecting the electrical connector, and removing and replacing the switch.

2. Turn Signal Switch Failure

Symptoms of Turn Signal Switch Failure

  • Clicking noise from the turn signal switch when driving down the road, as if the turn signal is trying to turn on

How to Fix Turn Signal Switch Failure

Replace the multi-function switch.

3. Front Wheel Bearing Failure

Symptoms of Bad Front Wheel Bearings

  • Whirring helicopter or airplane sound coming from the wheels that increases or decreases in volume when turning

How to Fix Bad Front Wheel Bearings

To check the wheel bearings, grab the tire from the 12 and 6 o’clock position and shake it in and out, feeling for excessive play or looseness. You may also be able to hear the bad wheel bearing during this.

Steps to replace the front wheel bearings include removing the front tires and brake caliper and rotor to access the front wheel bearing.

4. Encoder Motor Failure—Four Wheel Drive Problems

Symptoms of a Failing Encoder Motor

  • 4WD isn’t working
  • Service 4WD light is on for code C0327

Causes of Four Wheel Drive Problems on the 1st Gen GMC Sierra 1500

The code indicates a sensor inside the encoder motor is defective, which shuts down the 4WD system.

How to Fix a Bad Encoder Motor

Check the electrical connectors and wires for corrosion or damage. Replacing the encoder motor requires removing the front driveshaft. The encoder motor can be disassembled to replace the sensor separately.

5. Bad Front Impact Sensors

Symptoms of Bad Front Impact Sensors

  • Air bag light is on
  • B0100 Code

Causes of Bad Front Impact Sensors

The front impact sensors are located at the front of the vehicle at the base of the radiator. They tend to fail from corrosion. The sensor’s bolt can crack the sensor, allowing moisture to sneak in and cause corrosion.

How to Fix Bad Front Impact Sensors

Steps to replace the sensor include disconnecting the battery, disconnecting the sensor, and removing the bolt from the sensor.

1st Generation GMC Sierra 1500 Model Years

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Top 5 GMC Sierra Problems - 1st Generation (1999 to 2006) - 1A Auto
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Top 5 GMC Sierra Problems - 1st Generation (1999 to 2006) - 1A Auto
Learn how to find and fix 1st generation 1999 to 2006 GMC Sierra problems like four wheel drive problems and bad wheel bearings as our experts review its top 5.
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1A Auto
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