U0651: Lost Communication With EGR Sensor A

What it means

A control module has stopped receiving expected network messages from EGR sensor A. The sensor's function and the effect on EGR operation depend on the vehicle's system design.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

EGR sensor A reports a measurement used by the vehicle's exhaust-gas recirculation system; its exact role varies by design. This code sets when a module stops receiving the expected network messages from sensor A, which can prevent the system from controlling or verifying EGR operation.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Warning light or message related to the affected system
• EGR operation may be affected

How to diagnose it

1. Record freeze-frame data and scan all modules for EGR and communication codes to identify when sensor A messages disappeared.
2. Check live data for the sensor A reading and whether it updates under the conditions when EGR is commanded.
3. Inspect EGR sensor A's connector and network wiring for looseness, corrosion, heat damage, or chafing.
4. Check power and ground at sensor A or its associated module using the manufacturer's wiring information.
5. Test the network circuit for opens or shorts, then assess sensor A or its module if wiring and electrical feeds pass.

Common fixes

• Reconnect or clean the EGR sensor A connector.
• Repair damaged network wiring or connector terminals serving sensor A.
• Restore the sensor module's power or ground.
• Replace EGR sensor A or its module if the circuits pass but communication remains lost.

Can I keep driving?

If the engine runs normally, a short trip may be possible, but avoid heavy loads if power or smoothness worsens. Loss of EGR feedback can increase emissions and affect engine performance.