OBD Guide
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U18A1

Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus

U18A1 is an OBD-II diagnostic trouble code meaning: Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus. Common causes: malfunction of the coolant temperature control module, open or short circuit in the can bus circuit. Estimated repair cost: $56–167.

Severity
🔴 High
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$56–167 (est.)

Symptoms

  • Check Engine light comes on
  • Reduced vehicle performance
  • Incorrect operation of the cooling system
  • Possible warnings for high voltage system faults
  • Increased energy consumption in electric cars

Causes

  • Malfunction of the coolant temperature control module
  • Open or short circuit in the CAN bus circuit
  • Problems with connectors or wiring harness
  • Malfunction of other modules in the CAN network
  • Interference on the CAN bus

How to Fix

  1. Check the integrity of the wiring harness and connectors
  2. Check the voltage and resistance in the CAN bus circuit
  3. Scan other modules for communication errors
  4. Replace the coolant temperature control module if necessary
  5. Repair only from an authorized dealer

Related codes

U18A0U18A2U18A3

FAQ

What does the U18A1 code mean?

U18A1 is an OBD-II diagnostic trouble code that indicates: Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus

What causes a U18A1 error code?

The most common causes of U18A1 include: Malfunction of the coolant temperature control module; Open or short circuit in the CAN bus circuit; Problems with connectors or wiring harness; Malfunction of other modules in the CAN network.

How do I fix a U18A1 diagnostic trouble code?

To fix U18A1: Check the integrity of the wiring harness and connectors. Check the voltage and resistance in the CAN bus circuit. Scan other modules for communication errors. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with U18A1?

Do not drive — repair immediately

How much does it cost to fix U18A1?

The estimated repair cost for U18A1 is $56–167. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat