OBD Guide
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B2791

Communication Condition Failure Between ECM

B2791 is an OBD-II diagnostic trouble code meaning: Communication Condition Failure Between ECM. Common causes: open or shorted wiring harness, oxidation of ecm connector contacts. Estimated repair cost: $56–222.

Severity
🔴 High
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$56–222 (est.)

Symptoms

  • Check Engine light comes on
  • Loss of engine power
  • Incorrect transmission operation
  • Disabling security systems

Causes

  • Open or shorted wiring harness
  • Oxidation of ECM connector contacts
  • CAN bus fault
  • ECM software failure
  • Module power problems

How to Fix

  1. Check the integrity of the ECM wiring harness and connectors
  2. Diagnose the CAN bus for breaks/short circuits
  3. Check ECM power supply and ground
  4. Update ECM firmware (if necessary)
  5. Replace damaged components

Related codes

U0100U0121B2792

FAQ

What does the B2791 code mean?

B2791 is an OBD-II diagnostic trouble code that indicates: Communication Condition Failure Between ECM

What causes a B2791 error code?

The most common causes of B2791 include: Open or shorted wiring harness; Oxidation of ECM connector contacts; CAN bus fault; ECM software failure.

How do I fix a B2791 diagnostic trouble code?

To fix B2791: Check the integrity of the ECM wiring harness and connectors. Diagnose the CAN bus for breaks/short circuits. Check ECM power supply and ground. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B2791?

Do not drive — repair immediately

How much does it cost to fix B2791?

The estimated repair cost for B2791 is $56–222. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat