P0408Powertrain
Powertrain · SAE
EGR Position Sensor B Circuit High
Meaning
Voltage on EGR position sensor channel B is above the maximum threshold. The same cause, symptom, and diagnostic pattern as P0406 applies to sensor channel B.
Common causes
- Open circuit in channel B signal wire
- Short to Vref on channel B circuit
- Internal sensor failure with short to high on channel B
- Damaged connector
Symptoms
- MIL illuminated
- EGR position feedback degraded
- Possible detonation
Severity
Moderate — EGR control is compromised, resulting in increased NOx emissions.
What to do
- Check channel B signal wire for open circuit or short to Vref
- Measure channel B signal pin voltage (expected range 0.5–4.5 V)
- Inspect connector
- Replace sensor if channel B wiring checks out