P0408 OBD II Trouble Code Exhaust Gas Recirculation Sensor B Circuit High

Detailed information on troubleshooting and repairing a P0408 DTC code which has to do with the EGR Sensor B circuit high. Also includes links to relevant forum topics on the code.

Symptoms of P0408 OBD II Trouble Code

  • Increase in combustion temperatures (and NOx emissions)
  • MIL (Malfunction indicator lamp) illumination
  • Possible surging while driving
  • Possible intermittent stall

Common Causes of P0408 OBD II Trouble Code

  • EGR sensor signal circuit shorted to B+ (battery voltage)
  • EGR sensor signal circuit shorted to the 5 volt reference circuit to EGR
  • EGR sensor ground circuit open
  • EGR sensor signal circuit open
  • Bad EGR (internal failure on EGR sensor or solenoid)
  • Debris caught in valve and holding it open or closed