What it means
A control module has stopped receiving expected messages from the all terrain control module. Terrain or off-road functions managed by that module may be limited or unavailable.
How it works
The all terrain control module communicates with other modules to coordinate terrain or off-road features. U0138 sets when expected network messages from that module stop arriving, which may disable those features.
Common causes
Most likely first.
- All terrain control module power or ground fault
- Damaged network wiring or connector
- All terrain control module failure
- Low system voltage
Symptoms
- Terrain-control warning or message
- Terrain or off-road functions may be unavailable
- Other communication codes
How to diagnose it
- Scan all modules and review freeze-frame data for U0138 alongside low-voltage or related network codes.
- Check battery and charging-system condition, since low voltage can interrupt the all terrain module's communications.
- Inspect the all terrain control module connector and harness for looseness, corrosion, water, or physical damage.
- Check its power and ground circuits under load against the manufacturer's specification using a wiring diagram.
- Test the network wiring to the all terrain control module for opens, shorts, and poor connections using the manufacturer's procedure.
- If those circuits are sound, check whether the module responds to a scan tool before considering replacement or configuration.
Common fixes
- Restore battery or charging-system performance if voltage is low.
- Reconnect or repair a loose or corroded all terrain module connector.
- Repair damaged network wiring to the all terrain control module.
- Repair the module's power or ground fault.
- Replace and configure the all terrain control module if it remains unresponsive with sound circuits.
Can I keep driving?
Avoid off-road routes and terrain settings that depend on the all terrain system while the warning is present. Those functions may be unavailable, reducing the vehicle's ability to manage traction or terrain conditions.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.