U040CInvalid Data Received From Exhaust Gas Recirculation Control Module B
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- U040C concerns a second, separately networked EGR control unit, B. Two units appear on engines with separate high- and low-pressure recirculation paths, common on modern diesels, or with one EGR valve per cylinder bank; which one counts as B is up to the maker. The engine controller logs U040C when module B keeps talking but its content fails validation, while module A may still deliver clean data, which narrows the search to B's branch. Public manufacturer material and the NHTSA bulletins are silent on U040C, so its limits are not known; checks of counter and checksum as in GM's 2025 tables are the common pattern. With one EGR path unverified the controller usually closes it, NOx rises, and the MIL is expected because CARB treats EGR as a monitored system. U010B is lost contact, U040B module A.
- What you may notice
- Check engine light
- Reduced power, more smoke or higher fuel consumption
- Likely causes
- PossibleElectronics or position sensor of EGR actuator B delivering implausible values
- PossibleConnector or bus line in the branch of module B damaged by heat or moisture
- RareModule B with software that does not match the engine controller
- 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.