Damaged, corroded, or loose wiring or connector pins on the CAN bus circuit between the ECM and EGR control module B; Failed EGR control module B (internal communication fault or power/ground issue); Low or unstable battery voltage or a poor ground connection affecting module communication; Open or shorted CAN bus wiring harness, often from chafing or rodent damage; Software or calibration issue in the EGR module or ECM requiring a reflash; Aftermarket accessories or poor previous repairs tapping into the CAN bus and corrupting signals

DTC codes / U04xx · Invalid data received from a module / U040C

U040CInvalid Data Received From Exhaust Gas Recirculation Control Module B

U040C is a communication fault where the engine control module (ECM) or another primary controller receives invalid or missing data from the exhaust gas recirculation (EGR) control module B over the vehicle's controller area network (CAN) bus. The computer has detected that the EGR module's messages are either absent, corrupted, or outside expected parameters, so it cannot trust the EGR system's status or commands.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaInvalid data received from a module

Symptoms you may notice

Illumination of the check engine light (malfunction indicator lamp) with no other obvious drivability complaint
Rough idle or stumbling when the EGR system is commanded to open, especially during light-throttle cruise
Intermittent hesitation or surge during acceleration as the ECM loses EGR feedback
Reduced fuel economy if the ECM defaults to a rich or non-EGR operating strategy
Possible failure of the EGR monitor to complete, preventing other readiness tests from running
Often no symptoms besides the warning light when the fault is purely a communication glitch

Common causes, most likely first

Damaged, corroded, or loose wiring or connector pins on the CAN bus circuit between the ECM and EGR control module B
Failed EGR control module B (internal communication fault or power/ground issue)
Low or unstable battery voltage or a poor ground connection affecting module communication
Open or shorted CAN bus wiring harness, often from chafing or rodent damage
Software or calibration issue in the EGR module or ECM requiring a reflash
Aftermarket accessories or poor previous repairs tapping into the CAN bus and corrupting signals

How to diagnose and fix it

Verify battery voltage and charge the battery if low, then clear the code and retest to see if it returns immediately
Inspect the EGR control module B connector and the ECM connector for corrosion, loose pins, or pushed-back terminals
Perform a CAN bus continuity and resistance check (typically 60 ohms across the bus) to rule out wiring faults
Check power and ground supplies at the EGR control module B with a multimeter under load
Use a scan tool to monitor live EGR module data and confirm whether the module is communicating at all
If wiring and power are good, substitute a known-good EGR control module B and retest
After repair, clear codes and complete a full drive cycle to confirm the EGR monitor runs and the code does not reset

What U040C really tells you about the EGR module

U040C is a communication code, not a performance code, so replacing the EGR valve or cleaning the EGR passages will not fix it unless the module itself is faulty.
A weak or failing battery is a common hidden cause; modules can drop off the CAN bus during cranking and set U040C without any hard wiring fault.
The EGR control module B may be a separate module from the main EGR valve on some vehicles, so confirm the exact component location before ordering parts.
Aftermarket alarms, remote starters, or phone chargers plugged into the diagnostic port can corrupt CAN bus signals and trigger U040C intermittently.
This code can be stored alongside U0100 or U040D if the same bus fault affects multiple modules, so always check for other communication codes first.

Can I keep driving with U040C?

You can generally drive the vehicle with U040C set, but avoid heavy acceleration and long uphill pulls because the ECM may not command EGR correctly, which can increase combustion temperatures. If the check engine light flashes or you notice rough running, have it diagnosed promptly to prevent damage to the EGR system or catalytic converter.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.