U040B: Invalid Data Received From Exhaust Gas Recirculation Control Module A

What it means

A control module has received data from exhaust gas recirculation control module A that it considers invalid or implausible. Emissions or engine operation may be affected; specific effects depend on the vehicle.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

Exhaust gas recirculation control module A reports EGR system status and related operating data to other modules over the vehicle network. U040B sets when a receiving module rejects a message from EGR module A as implausible; it does not by itself prove that the EGR valve or passage is faulty.

Common causes

Most likely first.

1. Implausible or incorrect EGR control module data
2. Software or configuration incompatibility
3. Intermittent network data corruption

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules and save freeze-frame data to identify the receiving module and any EGR, engine, or network codes present with U040B.
2. Check live data for EGR module A status and related commanded or reported values, noting missing or implausible readings.
3. Inspect module A's connector and visible network wiring for loose pins, corrosion, heat damage, or chafing.
4. Check EGR module A power and ground, then test its related sensor and signal circuits against the manufacturer's specification.
5. Inspect the EGR components and passages associated with module A for damage or blockage if the scan data also points to an EGR operating problem.
6. If wiring and inputs are sound, verify module A configuration and software compatibility and investigate network faults using the manufacturer's diagnostic procedure.

Common fixes

• Repair damaged or corroded wiring or connector terminals at EGR control module A.
• Repair a failed power, ground, or sensor circuit identified during testing.
• Clean or repair an EGR component or passage if inspection confirms a restriction or mechanical fault.
• Correct module A software or configuration incompatibility.
• Replace EGR control module A only if testing confirms an internal fault.

Can I keep driving?

Avoid hard acceleration or long trips if the engine runs poorly or power is limited; an EGR control or emissions fault can worsen drivability and emissions. Stop if the engine overheats, stalls repeatedly, or becomes unsafe to control.