OBD Guide
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C1203

ECM Communication Circuit Malfunction

C1203 is an OBD-II diagnostic trouble code meaning: ECM Communication Circuit Malfunction. Common causes: damaged wiring harness, oxidized or loose connectors. Estimated repair cost: $56–333.

Severity
🔴 High
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$56–333 (est.)

Symptoms

  • Unstable engine operation
  • Power dips
  • Check Engine Light Illuminates
  • Problems starting the engine

Causes

  • Damaged wiring harness
  • Oxidized or loose connectors
  • Faulty Engine Control Module (ECM)
  • Short circuit in communication circuit
  • ECM power problems

How to Fix

  1. Check wiring harness for damage
  2. Inspect ECM connectors for oxidation or damage
  3. Check ECM power and ground
  4. Scan the system for additional errors
  5. Replace ECM or wiring harness if necessary

Related codes

C1201C1202P0606

FAQ

What does the C1203 code mean?

C1203 is an OBD-II diagnostic trouble code that indicates: ECM Communication Circuit Malfunction

What causes a C1203 error code?

The most common causes of C1203 include: Damaged wiring harness; Oxidized or loose connectors; Faulty Engine Control Module (ECM); Short circuit in communication circuit.

How do I fix a C1203 diagnostic trouble code?

To fix C1203: Check wiring harness for damage. Inspect ECM connectors for oxidation or damage. Check ECM power and ground. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with C1203?

Limited driving only, diagnose soon

How much does it cost to fix C1203?

The estimated repair cost for C1203 is $56–333. Actual cost depends on your vehicle, location, and labor rates.

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