EGR Sensor B Circuit High
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.
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.
Real-world scan data
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
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?+
Can I just clear P0408?+
Related codes
Read & clear P0408 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.