U0651 code meaning
Lost Communication With EGR Sensor A
Network system Generic code U06xx codes Check engine light
What U0651 means
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.
U0651 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0651
- MIL on from the first trip
- EGR switched off, possibly louder combustion
- EGR monitor not ready
Common causes of U0651
- Most likelySENT line to the EGR valve damaged by heat or chafing
- PossibleEGR valve connector corroded or loose
- PossiblePosition sensor in the EGR valve failed
- Less likelyEngine controller input fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EGR sensor aVehicle bus wiring
What each part of U0651 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 51 | The exact fault in that area. |
What to do next
- Note U0651 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0651
What does U0651 mean?
U0651 means "Lost Communication With EGR Sensor A". EGR sensors A to D are generic slots: a maker may assign them to valve position, pressure or another EGR measurement. It is a generic code, so it means the same on every make.
Is it safe to drive with U0651?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U0651 fail an emissions test?
Yes, it can. U0651 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0651 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0651 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.