Code
U1138
HYUNDAI
U — Network/User
Fan Operation Error(Fan is running although should be off)
Views:
UK: 18
EN: 37
RU: 29
AI status
Completed
Completed
100%
Causes
- Stuck or welded fan relay (stays closed)
- Shorted fan control wiring (power or ground) causing motor to run
- Faulty fan motor that receives unintended power
- Faulty fan control module or fan driver in ECM/BCM
- Incorrect temperature or sensor input commanding fan on (ECT sensor, HVAC inputs)
- CAN/Circuit communication error between ECM, BCM and fan control module
Symptoms
- Cooling fan runs continuously or intermittently when engine is cold or should be off
- Battery drain with vehicle off (if fan runs after shutoff)
- Fan noise at unexpected times
- DTC stored and MIL/cluster message may appear depending on model
- Possible HVAC performance changes (if related to blower or radiator fan control)
What to check
- Read all stored codes and freeze frame data from ECM, BCM and any fan control module
- Inspect fuses and fan relay(s) for correct part and signs of heat or welding
- Visually inspect wiring, connectors and grounds at fan motor, relay and control module
- Check coolant temperature sensor voltage/temperature values with a scan tool
- Verify CAN bus communication between modules (no bus errors, valid messages)
- Backprobe relay coil and fan motor power/ground circuits with key ON and engine OFF
Signal parameters
- Fan motor supply voltage (battery) — should be ~12V when relay closed, 0V when open
- Fan motor ground continuity — near 0 ohms to chassis when connected
- Relay coil control voltage from ECM/BCM — typically 0V or switched ground/PWM when commanded
- PWM duty cycle or frequency on fan control line (if module uses PWM)
- Coolant temperature sensor voltage/ECU-reported coolant temperature
- CAN bus error counters and message rates between ECM and BCM
Diagnostic algorithm
- Connect a full-function scan tool. Record U1138 and any related codes from ECM, BCM and fan module. Capture freeze-frame and live data (ECT, fan status, commands).
- Confirm symptom: with ignition ON (engine off) verify whether fan is running and note whether module reports fan ON and whether command is OFF.
- Visually inspect connectors, wiring and grounds at fan motor, relay(s) and control module. Repair any corrosion or damage.
- Check fuses and swap/inspect fan relay. If relay contacts are welded, replace relay and retest.
- Backprobe the relay control circuit. Verify whether the control module is commanding the relay to be ON (voltage or ground) when it should be OFF. If module is not commanding ON but relay/coils are energized, suspect wiring short or stuck relay.
- With the fan running unexpectedly, isolate power: disconnect the fan motor connector (or relay output) to see if fan stops. If fan continues, suspect alternate feed or internal module stuck. If fan stops, measure current draw and motor resistance.
- Apply 12V directly to fan motor (bench test) to confirm motor operation and that it does not draw excessive current or have internal short that could cause control anomalies.
- Check coolant temperature sensor readings and compare to actual temperature. Replace sensor if reading incorrect and commanding fan on.
- Check CAN bus for errors; if communication faults present, trace and repair bus issues or faulty module. Reprogram/update module software if manufacturer bulletin applies.
- Clear codes and retest under conditions that previously set the fault. If fault returns, isolate component by substitution (relay, fan motor, control module) as required per results.
- If module replacement is necessary, follow OEM programming and initialization procedures.
Likely causes
- Stuck relay supplying continuous battery power to fan
- Short to battery on fan motor feed or relay output
- Fan control transistor inside module failed closed
- Open/incorrect signal from engine coolant temperature sensor causing continuous demand
- Intermittent CAN communication failure causing inconsistent status reporting
Fault status
Status
Fan running when commanded OFF. Code set when module detects fan state active while control command indicates OFF (possible relay, wiring, motor, sensor, or communication fault).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Repair manuals
Manual library for HYUNDAI
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Code
U1138
Other
U — Network/User
SCP (J1850) Invalid or Missing Data for Primary Id
Views:
UK: 28
EN: 46
RU: 34
AI status
Completed
Completed
100%
Causes
- Stuck or welded fan relay (stays closed)
- Shorted fan control wiring (power or ground) causing motor to run
- Faulty fan motor that receives unintended power
- Faulty fan control module or fan driver in ECM/BCM
- Incorrect temperature or sensor input commanding fan on (ECT sensor, HVAC inputs)
- CAN/Circuit communication error between ECM, BCM and fan control module
Symptoms
- Cooling fan runs continuously or intermittently when engine is cold or should be off
- Battery drain with vehicle off (if fan runs after shutoff)
- Fan noise at unexpected times
- DTC stored and MIL/cluster message may appear depending on model
- Possible HVAC performance changes (if related to blower or radiator fan control)
What to check
- Read all stored codes and freeze frame data from ECM, BCM and any fan control module
- Inspect fuses and fan relay(s) for correct part and signs of heat or welding
- Visually inspect wiring, connectors and grounds at fan motor, relay and control module
- Check coolant temperature sensor voltage/temperature values with a scan tool
- Verify CAN bus communication between modules (no bus errors, valid messages)
- Backprobe relay coil and fan motor power/ground circuits with key ON and engine OFF
Signal parameters
- Fan motor supply voltage (battery) — should be ~12V when relay closed, 0V when open
- Fan motor ground continuity — near 0 ohms to chassis when connected
- Relay coil control voltage from ECM/BCM — typically 0V or switched ground/PWM when commanded
- PWM duty cycle or frequency on fan control line (if module uses PWM)
- Coolant temperature sensor voltage/ECU-reported coolant temperature
- CAN bus error counters and message rates between ECM and BCM
Diagnostic algorithm
- Connect a full-function scan tool. Record U1138 and any related codes from ECM, BCM and fan module. Capture freeze-frame and live data (ECT, fan status, commands).
- Confirm symptom: with ignition ON (engine off) verify whether fan is running and note whether module reports fan ON and whether command is OFF.
- Visually inspect connectors, wiring and grounds at fan motor, relay(s) and control module. Repair any corrosion or damage.
- Check fuses and swap/inspect fan relay. If relay contacts are welded, replace relay and retest.
- Backprobe the relay control circuit. Verify whether the control module is commanding the relay to be ON (voltage or ground) when it should be OFF. If module is not commanding ON but relay/coils are energized, suspect wiring short or stuck relay.
- With the fan running unexpectedly, isolate power: disconnect the fan motor connector (or relay output) to see if fan stops. If fan continues, suspect alternate feed or internal module stuck. If fan stops, measure current draw and motor resistance.
- Apply 12V directly to fan motor (bench test) to confirm motor operation and that it does not draw excessive current or have internal short that could cause control anomalies.
- Check coolant temperature sensor readings and compare to actual temperature. Replace sensor if reading incorrect and commanding fan on.
- Check CAN bus for errors; if communication faults present, trace and repair bus issues or faulty module. Reprogram/update module software if manufacturer bulletin applies.
- Clear codes and retest under conditions that previously set the fault. If fault returns, isolate component by substitution (relay, fan motor, control module) as required per results.
- If module replacement is necessary, follow OEM programming and initialization procedures.
Likely causes
- Stuck relay supplying continuous battery power to fan
- Short to battery on fan motor feed or relay output
- Fan control transistor inside module failed closed
- Open/incorrect signal from engine coolant temperature sensor causing continuous demand
- Intermittent CAN communication failure causing inconsistent status reporting
Fault status
Status
Fan running when commanded OFF. Code set when module detects fan state active while control command indicates OFF (possible relay, wiring, motor, sensor, or communication fault).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Repair manuals
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2,736
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