Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / U1138 — Fan Operation Error(Fan is running although should be off)

U1138 — Fan Operation Error(Fan is running although should be off)

Detailed page for trouble code U1138.

34,405codes
59brands
11,914generic
22,491specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

U1138

HYUNDAI U — Network/User

Fan Operation Error(Fan is running although should be off)

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

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

  1. 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).
  2. Confirm symptom: with ignition ON (engine off) verify whether fan is running and note whether module reports fan ON and whether command is OFF.
  3. Visually inspect connectors, wiring and grounds at fan motor, relay(s) and control module. Repair any corrosion or damage.
  4. Check fuses and swap/inspect fan relay. If relay contacts are welded, replace relay and retest.
  5. 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.
  6. 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.
  7. 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.
  8. Check coolant temperature sensor readings and compare to actual temperature. Replace sensor if reading incorrect and commanding fan on.
  9. 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.
  10. 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.
  11. 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

P0480 P0481 P0482 U0100 U0121
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .