P0408
EGR Sensor B Circuit High
EGR / emissions
Generic OBD-II
Medium
What it means
P0408 means the EGR (exhaust gas recirculation) position sensor "B" is reporting a high, out-of-range voltage. The ECM uses this sensor to know how far the EGR valve is open; a bad reading can upset EGR flow, causing rough running or hesitation and an emissions failure — but it does not stop the engine from starting.
Medium
Can I keep driving? You can keep driving — you may notice slightly rough running or hesitation and it will fail an emissions test, but it won't stop the car.
Common symptoms
What you'll notice
- Check-engine light on
- Possible rough idle or hesitation
- Slight loss of power
- Failed emissions test
Common causes
Most likely first
- EGR position sensor B signal wiring shorted to voltage or openLikely
- Faulty EGR sensor BCommon
- Poor or corroded connectorCommon
- Sticking EGR valve throwing off the readingLess often
- ECM fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and inspect the EGR sensor B connector and wiring for a short to voltage or an open.
- Compare the sensor's signal with the actual EGR valve position.
- Test and replace the EGR position sensor if out of spec.
- Inspect the EGR valve's operation for sticking.
- Repair the wiring/connector, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0408?+
Generally yes, short-term — expect an emissions failure and possible hesitation until it's fixed.
Can I just clear P0408?+
You can, but it returns until the sensor or its circuit is repaired.
Related codes
Often seen with P0408
Read & clear P0408 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX