EGR Valve


Before attempting to troubleshoot or repair a suspected exhaust gas recirculation (EGR) system on a vehicle, the following conditions should be checked and be within specifications.

  • Engine is mechanically sound.
  • Injection system is operating properly.
  • Mechanical-vacuum advance is properly adjusted or the electronic advance system is operating properly.

If one or more of these conditions is faulty or operating incorrectly, perform the necessary tests and services to correct the problem before servicing the EGR system.

Typical EGR valve. Courtesy of Chevrolet Motor Division-GMC.

Before attempting any tests of the EGR system, visually inspect the condition of all vacuum hoses for kinks, bends, cracks, and flexibility. Replace defective hoses as required. Check vacuum hose routing. (See the underhood decal or the manufacturer's service manual for correct routing.) Correct any misrouted hoses. If the emissions system if fitted with an exhaust-gas-recirculation valve position (EVP) sensor, the wires routed to it should also be checked.

If the EGR valve remains open at idle and low engine speed, the idle operation is rough and surging occurs at low speeds. When this problem is present, the engine may hesitate on low-speed acceleration or stall after deceleration or after a cold start. If the EGR valve does not open, engine detonation occurs. When a defect occurs in the EGR system, a diagnostic trouble code (DTC) is usually set in the powertrain control module (PCM) memory.

Typical computer-controlled EGR system. Reprinted with permission of Ford Motor Company.

In many EGR systems, the PCM uses imputs from the engine coolant temperature (ECT) sensor, throttle position sensor (TPS), and manifold absolute pressure (MAP) sensors to operate the EGR valve. Improper EGR operation may be caused by a defect in one of these sensors. A scan tester may be connected to the data link connector (DLC) to check for an EGR DTC or a DTC from another sensor which may affect EGR operation. The cause of any DTCs should be corrected before any further EGR diagnosis.