Symptoms
- AWD or 4WD icon lit, sometimes with a message like 'service AWD system'
- Possible unusual noise from the drivetrain
- May notice reduced traction in slippery conditions
Likely causes
- CommonLow or degraded transfer case/differential fluidThese components need proper fluid levels to engage correctly.
- CommonFaulty wheel speed sensorAWD/4WD systems often rely on the same sensors as ABS and traction control.
- PossibleFailing transfer case motor or actuatorControls engagement between two- and four-wheel drive modes.
- PossibleOverheating transfer case from prolonged slippageCan happen from stuck wheels in mud or snow.
- Less commonWiring or module faultLess common but possible in the drivetrain control system.
What to do
- Avoid activating 4WD/AWD-specific modes (like 4-low) until the light is diagnosed.
- Check for any unusual noises from underneath the vehicle when driving.
- Check fluid levels in the transfer case and differentials if accessible, or have a shop do it.
- Avoid situations requiring maximum traction, like deep snow or mud, until repaired.
- Have the code read at a shop familiar with your vehicle's drivetrain system.
- Get fluid changed, sensors replaced, or the transfer case serviced based on the diagnosis.
Tools and parts
Transfer case/differential fluidSearch: “transfer case fluid for your car make and model”
When to call a pro
See a mechanic before relying on 4WD/AWD in slippery or off-road conditions, since the system may not engage properly.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.