U0651Lost Communication With EGR Sensor A
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- EGR sensors A to D are generic slots: a maker may assign them to valve position, pressure or another EGR measurement. In GM's 2025 diesel table 25OBDG04B, which has both a high-pressure and a low-pressure EGR loop, sensor A is the SENT position sensor of the high-pressure valve. U0651 is set there if at least 480 out of 600 tests, one every 6.25 ms, find stale data with the line stuck low or high, a message error, or counters that stop, provided the relay supplies more than 11 V and no start is in progress; Type A, MIL in the first trip. A raw signal below 1 % of 5 V on the same sensor is P0405 instead. Other analog faults run through P0405 to P0409 and P046C. EGR flow monitoring stops while the position is missing.
- What you may notice
- MIL on from the first trip
- EGR switched off, possibly louder combustion
- EGR monitor not ready
- Likely causes
- LikelySENT line to the EGR valve damaged by heat or chafing
- PossibleEGR valve connector corroded or loose
- PossiblePosition sensor in the EGR valve failed
- RareEngine controller input fault
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.