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NOTEDigital EGR Valve Diagnosis
The digital EGR valve may be diagnosed with a scan tester. With theengine at normal operating temperature and the ignition switch off,connect the scan tester to the data link connector (DLC). Start theengine and allow the engine to operate at idle speed. Select EGRcontrol on the scan tester, and then energize EGR solenoid number onewith the scan tester. When this action is taken, the engine rpm shoulddecrease slightly. The engine rpm should drop slightly as each EGRsolenoid is energized with the scan tester. When the EGR valve does notoperate properly, check these items before replacing the EGR valve:

• Check the 12 V at the power supply wire on the EGR valve.

Digital EGR valve circuit. Courtesy of Oldsmobile Motor Division-GMC.

• Check the wires between the EGR valve and the powertrain control module (PCM).
• Remove the EGR valve, and check for plugged passages under the valve.

Linear EGR Valve Diagnosis
The linear EGR valve diagnosis procedure varies depending on thevehicle make and model year. Always follow the recommended procedure inthe vehicle manufacturer's service manual. The scan tester may be usedto diagnosis a linear EGR valve. The engine should be at normaloperating temperature prior to EGR valve diagnosis. Since the linearEGR valve has an EVP sensor, the actual pintle position may be checkedon the scan tester. The pintle position should not exceed 3% at idlespeed. The scan tester may be operated to command a specific pintleposition, such as 75%, and this commanded position should be achievedwithin two seconds. With the engine idling, select various pintlepositions and check the actual pintle position. The pintle positionshould always be within 10% of the commanded position. When the linearEGR valve does not operate properly:

• Check the fuse in the 12 V supply wire to the EGR valve.
• Check for open circuits, grounds, and shorts in the wires connected from the EGR valve winding to the PCM.
• Use a digital voltmeter to check for 5 v on the reference wire to the evp sensor.
• Check for excessive resistance in the EVP sensor ground wire.
• Leave the wiring harness connected to the valve, and remove thevalve. Connect a digital voltmeter from the pintle position wire at theEGR valve to ground, and manually push the pintle upward. The voltmeterreading should change from approximately 1 V to 4.5 V.

Linear EGR valve circuit. Courtesy of Chevrolet Motor Division-GMC.If the EGR valve did not operate properly on the scan tester and tests 1 through 5 are satisfactory, replace the valve.

Hi,

HOW TO INSPECT 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.




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.

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