U0138

Code

HYUNDAI U — Network/User

Lost Communication With All Terrain Control Module

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 13 EN: 18 RU: 14

AI status

Completed

ready

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Page language: EN

Causes

ATC module powered off or failed
Blown fuse or relay for ATC module power
Poor or open ground to the ATC module
Damaged, corroded, or disconnected wiring/connectors to the ATC module
CAN bus wiring fault (open, short to battery/ground, high resistance)
Failed termination resistor(s) or improper CAN bus topology

Symptoms

ATC / terrain management features disabled or inoperative
4WD/AWD system warnings or limited drive mode
Related warning lamp(s) or message on the cluster
Loss of other functions tied to ATC (traction control behaviors)
Possible multiple U0xxx communication codes present

What to check

Retrieve U0138 and any related codes and freeze frame data with a OEM-capable scan tool
Check battery voltage and charging system (low voltage can cause comm faults)
Inspect fuses and relays that supply the ATC module
Visually inspect ATC module connector for corrosion, bent pins, or water intrusion
Verify ATC module power and ground with a DVOM
Check for other U0xxx codes that indicate wider CAN bus issues

Signal parameters

High-speed CAN typical idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive)
Dominant state typical voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Bus termination: two 120 Ω resistors in parallel ≈ 60 Ω measured across CAN_H–CAN_L
Typical bus bit rates: 500 kbps or 250 kbps (verify vehicle spec)
ATC module should transmit a regular 'heartbeat' or status message — often every 100–1000 ms

Diagnostic algorithm

Connect an OEM-capable scan tool. Record U0138 and any other active or stored U-codes and freeze frame info.
Check battery voltage with key on/engine off and engine running. Ensure voltage is within specification.
Inspect and test fuses/relays supplying the ATC module. Replace any blown fuses and retest communication.
Visually inspect the ATC module connector and harness for corrosion, bent pins, water intrusion, or physical damage. Repair as necessary.
Backprobe and verify module power (B+) and ground(s) with the harness connected. Repair wiring if power/ground missing or intermittent.
With ignition on, measure CAN_H and CAN_L at the ATC module connector. Verify recessive and dominant voltages and check for proper termination resistance (~60 Ω across CAN_H–CAN_L).
If CAN voltages or termination are incorrect, trace wiring for shorts to battery/ground or opens. Repair wiring or connectors.
Use a scan tool or oscilloscope to verify message traffic on the CAN bus and confirm whether the ATC module transmits any frames. Check for bus collisions or invalid frames.
Disconnect or remove recently added aftermarket devices that may interfere with the CAN bus and retest.
If wiring, power, ground, and bus integrity are good but no communication from the ATC module, consider module failure. Verify software compatibility and reprogram/update module if required by manufacturer.
If replacement is performed, program/configure the new module per OEM procedures and clear codes. Verify operation and road-test to confirm resolution.
If intermittent, perform wiggle tests, wet tests (if safe and appropriate), and load tests to reproduce fault and locate intermittent connector/harness faults.

Likely causes

Loose, corroded, or disconnected ATC module connector
No power or ground to the ATC module (fuse/relay fault)
CAN bus wiring short or open between ATC and other modules
Failed ATC module
Intermittent communication due to water/damage at connector

Fault status

⚠️ Status

U0138 — Lost Communication With All Terrain Control Module. The ATC module is not responding on the vehicle CAN network; check module power/ground, connectors, wiring, and CAN bus integrity.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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