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U0651 — Lost Communication Egr Sensor

Generic OBD-II · all makesNetwork / communication

OBD-II code U0651 indicates that the powertrain control module (PCM) has lost communication with the EGR (Exhaust Gas Recirculation) sensor or its associated module. This typically means the sensor or its circuit is not sending expected data, disrupting emissions control and engine performance.

Symptoms

What causes it — most likely first

1. Faulty EGR sensor or position sensor

The EGR sensor itself may have failed, providing no signal or an erratic signal to the PCM. This is the most common cause of U0651.

2. Wiring or connector issues in the EGR sensor circuit

Damaged, corroded, or loose wiring or connectors between the EGR sensor and the PCM can disrupt communication. This includes open or short circuits in the harness.

3. Failed EGR valve or actuator

A malfunctioning EGR valve or its actuator may prevent the sensor from operating correctly, leading to a loss of communication with the PCM.

4. Blown fuse or faulty relay in the EGR circuit

A blown fuse or defective relay supplying power to the EGR sensor or its module can cause a complete loss of communication.

5. Communication bus issues (CAN bus or LIN bus)

Problems with the vehicle's communication network, such as a short or open in the CAN or LIN bus lines, can prevent data transmission between the EGR sensor and PCM.

6. PCM software or hardware failure (rare)

While uncommon, a fault in the PCM's software or hardware could disrupt communication with the EGR sensor. This is typically a last-resort diagnosis after other causes are ruled out.

How it's diagnosed

  1. Retrieve and document all stored trouble codes, including pending and history codes, to identify related issues.
  2. Inspect the EGR sensor and its wiring/connector for visible damage, corrosion, or loose connections. Repair or replace as needed.
  3. Test the EGR sensor's voltage and signal output using a multimeter or scan tool to verify proper operation. Compare readings to manufacturer specifications.
  4. Check the EGR valve and actuator for proper function. Ensure the valve moves freely and responds to commands from the PCM.
  5. Inspect fuses and relays related to the EGR system. Replace any blown fuses or faulty relays and retest.
  6. Use an oscilloscope or scan tool to check the CAN or LIN bus communication lines for proper signal integrity. Repair any shorts, opens, or signal issues.
  7. If all other causes are ruled out, consider reflashing or replacing the PCM, though this is rarely necessary for U0651.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0649 — Lost Communication Coolant Pump DU0650 — Lost Communication Exhaust Pressure CoU0652 — Lost Communication Egr Sensor BU0653 — Lost Communication Egr Sensor CU0654 — Lost Communication Diesel Intake Air FU0655 — Lost Communication Diesel Intake Air F

Frequently asked

Is the PCM usually the cause of U0651?

No, the PCM is rarely the cause of U0651. This code typically points to issues with the EGR sensor, wiring, or related components. Replacing the PCM should only be considered after all other potential causes have been thoroughly ruled out.

Can I drive with U0651 stored?

While the vehicle may still be drivable, driving with U0651 can lead to reduced fuel efficiency, increased emissions, and potential engine performance issues. It is recommended to diagnose and repair the issue as soon as possible.

Why does my scan tool show U0651 along with other communication codes?

U0651 often appears alongside other communication codes because it involves the vehicle's communication network (e.g., CAN or LIN bus). A fault in the network can affect multiple modules or sensors, leading to multiple codes.

Do I need to replace the EGR valve if U0651 is stored?

Not necessarily. U0651 specifically indicates a loss of communication with the EGR sensor, not the valve itself. However, if the EGR valve or its actuator is faulty, it may indirectly cause this code. Always diagnose the sensor and wiring first.