Damaged, corroded, or loose wiring or connector pins in the CAN bus circuit feeding the all terrain control module; Failed all terrain control module, often due to water intrusion or internal circuit board damage; Blown fuse or poor ground connection supplying power to the all terrain control module; Open or shorted CAN bus wiring between the all terrain module and the rest of the network; Low battery voltage or a weak charging system causing modules to drop offline intermittently; Another module on the same bus holding the network down and preventing communication; Software or configuration mismatch after module replacement or battery disconnection

DTC codes / U01xx · Lost communication with a control module / U0138

U0138Lost Communication with All Terrain Control Module

Q: What does code U0138 mean?

Lost Communication with All Terrain Control Module. U0138 is a communication fault that sets when the engine control module or another primary module on the controller area network (CAN) bus stops receiving messages from the all terrain control module, which is the module that manages off-road driving modes such as terrain response, hill descent, and differential lock strategies. The computer has detected a loss of the periodic heartbeat signal from that module rather than a mechanical failure inside the all terrain system itself.

U0138 is a communication fault that sets when the engine control module or another primary module on the controller area network (CAN) bus stops receiving messages from the all terrain control module, which is the module that manages off-road driving modes such as terrain response, hill descent, and differential lock strategies. The computer has detected a loss of the periodic heartbeat signal from that module rather than a mechanical failure inside the all terrain system itself.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Symptoms you may notice

Illumination of the check engine light or a dedicated all-wheel-drive or terrain system warning lamp
Terrain response or off-road driving mode selector becomes unresponsive or stuck in a default mode
Hill descent control and other off-road assistance features fail to engage
Multiple warning lights appear together because several modules share the same communication bus
Often no symptoms besides the warning light when the fault is intermittent
Vehicle may default to a normal road driving mode and refuse to switch into low-range or specialty modes

Common causes, most likely first

Damaged, corroded, or loose wiring or connector pins in the CAN bus circuit feeding the all terrain control module
Failed all terrain control module, often due to water intrusion or internal circuit board damage
Blown fuse or poor ground connection supplying power to the all terrain control module
Open or shorted CAN bus wiring between the all terrain module and the rest of the network
Low battery voltage or a weak charging system causing modules to drop offline intermittently
Another module on the same bus holding the network down and preventing communication
Software or configuration mismatch after module replacement or battery disconnection

How to diagnose and fix it

Verify battery voltage and charging system output, then clear the code and test-drive to see if it returns
Inspect the all terrain control module connector for corrosion, water intrusion, and backed-out pins
Check the fuse and ground circuit that powers the all terrain control module with a multimeter
Measure CAN bus resistance and voltage at the module connector to confirm the bus is intact
Perform a network communication test with a scan tool to see whether other modules also drop offline
If wiring and power are good, substitute a known-good module or perform module reprogramming as required
After repair, clear codes and complete a full drive cycle to confirm the module stays online

What the all terrain module actually controls

This code often sets after a battery replacement or jump-start because modules reboot in the wrong order and log a communication loss that never returns.
Water intrusion into the all terrain module connector is a common hidden cause, especially on vehicles that have been through deep water or pressure washing.
A single failed module on the CAN bus can pull the entire network down, so the all terrain module may be innocent while another module causes the silence.
Technicians who replace the all terrain module without checking bus resistance frequently find the new module sets the same code because the wiring fault remains.
Intermittent U0138 that appears only in cold or wet weather usually points to a connector pin tension problem rather than a failed module.

Can I keep driving with U0138?

The vehicle usually remains drivable in a default road mode, but off-road assistance features and specialty terrain modes will be unavailable, so avoid trails, steep descents, and low-traction situations until the fault is repaired. If the warning light is accompanied by reduced power or multiple system failures, have the vehicle inspected promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.