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P0408: Exhaust Gas Recirculation Sensor B Circuit High

Severity: Medium Arrange diagnosis soon. If the engine stalls, surges severely, or pings under load, avoid continued driving until the cause is checked.

What does P0408 mean?

The EGR feedback circuit identified as B reports too high a voltage. The fault can prevent accurate control because the computer no longer has a dependable measure of EGR position or operation.

Generic OBD-II definition: Exhaust Gas Recirculation Sensor B Circuit High. Confirm applicability in your vehicle service information.

Common causes

  • B signal shorted to voltage
  • Open sensor return or connection
  • Internal EGR sensor failure

Symptoms

  • Check engine light
  • Possible rough idle or surging
  • Sometimes no noticeable driving symptom

Diagnostic focus

A high B signal can coexist with normal A feedback. That distinction can help isolate a channel or harness fault instead of blaming the entire gas-flow system.

Can I keep driving with P0408?

Severity: Medium Arrange diagnosis soon. If the engine stalls, surges severely, or pings under load, avoid continued driving until the cause is checked.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

  • Inspect the B signal circuit for unwanted power
  • Verify the return and connector pin condition
  • Compare physical valve movement with reported feedback

Related codes

P0406
Exhaust Gas Recirculation Sensor A Circuit HighP0407
Exhaust Gas Recirculation Sensor B Circuit LowP0409
Exhaust Gas Recirculation Sensor A Circuit

Sources & review

Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.