U040BInvalid Data Received From Exhaust Gas Recirculation Control Module A
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- U040B refers to an exhaust gas recirculation system driven by its own electronics on the bus, for example a smart EGR valve actuator that receives position targets and returns its measured position. The code is set when that unit's replies reach the engine controller but fail plausibility or protection checks, so the controller can no longer verify how much exhaust gas flows back. U040B appears in no public manufacturer document and in none of the bulletins indexed by NHTSA. GM's 2025 tables show how such checks work on other emission-related modules: counter, protection value and checksum, a fail ratio such as 8 of 18 samples, then a MIL. CARB requires EGR flow to be monitored, so the code counts as emission-relevant; expect EGR to be switched off, higher NOx and possibly less power. U010A is lost contact, U040C module B.
- What you may notice
- Check engine light
- Reduced power or rough idle
- EGR flow codes stored alongside
- Likely causes
- PossibleElectronics or position sensor of the EGR actuator A delivering implausible values
- PossibleHeat-damaged connector or bus line at the EGR unit
- PossibleSoftware of engine controller and EGR module A out of step
- RareEGR control module A internally faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.