Emissions

P249A — EGR Cooler Bypass Control Circuit Open

Severity: medium Drive with care, to a shop

What P249A means

On diesel engines, the control unit uses a bypass valve to send exhaust gas either through the EGR cooler or around it. P249A is set when the unit sees an open circuit in the bypass valve control. As a result, EGR gas temperature and the intake mixture may not be regulated correctly.

Symptoms

  • Check engine light on
  • Possible reduced engine power
  • Rough idle or hesitation on acceleration
  • Related EGR efficiency or overheat codes
  • More exhaust smoke or higher fuel use

Possible causes

  1. Failed bypass valve actuator
  2. Open circuit in the control wiring
  3. Corroded or damaged connector
  4. Valve stuck by carbon buildup
  5. Carbon-blocked EGR passages
  6. Faulty EGR valve or position sensor
  7. Vacuum supply fault on vacuum-operated systems

How to diagnose

  1. Read codes and freeze frame data, and scan all modules for related faults
  2. Check battery voltage and ground condition
  3. Inspect the valve harness and connector for breaks, chafing and corrosion
  4. Test the control circuit from the control unit to the valve for continuity, power and ground
  5. Compare commanded and actual EGR position in live data
  6. Command the bypass valve with a scan tool and confirm it moves
  7. Remove and inspect the bypass valve, EGR valve and passages for carbon
  8. Check vacuum lines and the vacuum actuator where fitted

Common fixes

  • Repair the wiring or replace the damaged connector
  • Replace the bypass valve or its actuator
  • Clean the EGR valve and passages of carbon
  • Replace the EGR valve or position sensor if confirmed faulty
  • Replace damaged vacuum hoses
  • Clear the code and road test to confirm

Questions and answers

Can I drive with a P249A code?

Briefly, if power is normal and the engine is not overheating. Get it diagnosed soon, since carbon and heat can damage the EGR system.

What most often causes P249A?

Usually a broken wire or bad connector, or a bypass valve or actuator stuck with carbon. Start with a wiring inspection and a valve movement test.

Will clearing the code fix it?

No, not unless the cause is repaired. The code returns as soon as the control unit detects the open circuit again.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.