Before beginning testing procedures, refer to your vehicle's service manual. This is a general test procedure.
Test the exhaust gas recirculation (EGR) valve by using a vacuum gauge or hand vacuum pump. Follow these procedures for using either piece of test equipment.
- Disconnect a vacuum line connected to an intake manifold port.
- Put a vacuum gauge between the disconnect vacuum line and the intake manifold port.
- Connect a tachometer.
- Start the engine and gradually increase speed to 2,000 rpm with the transmission in neutral.
- The reading from the manifold vacuum gauge should be above 16 inches of vacuum. If not, there could be a vacuum leak or exhaust restriction. Before continuing to test the EGR, correct the problem of low vacuum.
Using a Hand Vacuum Pump to Check the Operation of the EGR Valve
- Check all vacuum lines for correct routing. Ensure that they are attached securely. Replace cracked, crimped, or broken lines.
- Remove the vacuum supply hose from the EGR valve port.
- Connect the vacuum pump to the port and supply 18 inches of vacuum. Observe the EGR movement. In some applications, a mirror may be held under the EGR valve to see the diaphragm movement. When the vacuum is applied, the diaphragm did not move or did not hold the vacuum, replace the valve.
- With the engine at normal operating temperature, check the vacuum supply hose to make sure there is no vacuum to the EGR valve at idle. Then plug the hose.
- Install a tachometer.
- On EFI engines (multi-point injection), disconnect the throttle air bypass valve solenoid.
- Observe the engine's idle speed. If necessary, adjust idle speed to the emission decal specification.
- Slowly apply 5 to 10 inches of vacuum to the EGR valve vacuum port using a hand vacuum pump. The idle speed should drop more than 100 rpm (the engine may stall), and then return to normal (greater than or equal to 25 rpm) again when the vacuum is removed.
- If the idle speed does not respond in this manner, remove the valve and check for carbon in the passages under the valve. Clean the passages as required or replace the EGR valve. Carbon may be cleaned from the lower end of the EGR valve with a wire brush, but do not emerse the valve in solvent, and do not sandblast the valve.
- If the EGR valve is operating properly, unplug and reconnect the EGR vacuum supply hose.
- Reconnect the the throttle air bypass valve solenoid, if removed.
Diagnosis of Negative Backpressure EGR Valve
With the engine at normal operating temperature and the ignition switch off, disconnect the vacuum hose from the EGR valve, and connect a hand vacuum pump to the vacuum fitting on the valve. Supply 18 in. Hg of vacuum to the EGR valve and observe the valve operation and the vacuum gauge. The EGR valve should open and hold the vacuum for 20 seconds. When the valve does not operate properly, replace the valve.
With 18 in. Hg supplied to the EGR valve from the hand pump, start the engine. The vacuum should drop to zero, and the valve should close. If the valve does not operate properly, replace the valve.
Diagnosis of Positive Backpressure EGR Valve
With the engine at normal operating temperature and running at idle speed, disconnect the vacuum hose from the EGR valve. Connect a hand vacuum pump to the EGR valve vacuum fitting, and operate the hand pump to supply vacuum to the valve. The vacuum should be bled off, and the EGR valve diaphragm and stem should not move. If the EGR valve does not operate properly, replace the valve.
Disconnect the EGR vacuum supply hose from the TBI unit and connect a long hose from this port directly to the EGR valve. Accelerate the engine to the 2,000 rpm and observe the ERG valve. The valve should open at this engine speed. Allow the engine to return to idle speed. The EGR valve should close. If the EGR valve does not open properly, remove the valve and check for a plugged or restricted exhaust passage under the valve. When these passages are not restricted, replace the valve.
Typical Procedure for Diagnosing a Positive Backpressure EGR Valve
- With the engine at normal operating temperature, disconnect the vacuum hose from the EGR valve.
- Connect the vacuum hose from a hand pump to the EGR valve vacuum fitting.
- With the engine idling, operate the hand pump to supply vacuum to the EGR valve. The vacuum should be bled off to zero on the hand pump gauge, and the EGR valve should not open. No change in engine operation should occur.
- Disconnect the EGR vacuum supply hose from the throttle body.
- Connect a long vacuum hose from the EGR vacuum port on the throttle body directly to the EGR valve vacuum fitting.
- Use a T fitting to connect a vacuum gauge in the direct vacuum line to the EGR valve.
- Start the engine, increase the rpm to 2,000, and observe the vacuum gauge. Vacuum should now be supplied to the EGR valve, and this valve should be opened.
Art courtesy of Delmar - Thomson Learning.
- Shut off the engine, disconnect the long vacuum hose and vacuum gauge, and reconnect the original EGR hoses.
Digital EGR Valve Diagnosis
The digital EGR valve may be diagnosed with a scan tester. With the engine at normal operating temperature and the ignition switch off, connect the scan tester to the data link connector (DLC). Start the engine and allow the engine to operate at idle speed. Select EGR control on the scan tester, and then energize EGR solenoid number one with the scan tester. When this action is taken, the engine rpm should decrease slightly. The engine rpm should drop slightly as each EGR solenoid is energized with the scan tester. When the EGR valve does not operate 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 the vehicle make and model year. Always follow the recommended procedure in the vehicle manufacturer's service manual. The scan tester may be used to diagnosis a linear EGR valve. The engine should be at normal operating temperature prior to EGR valve diagnosis. Since the linear EGR valve has an EVP sensor, the actual pintle position may be checked on the scan tester. The pintle position should not exceed 3% at idle speed. The scan tester may be operated to command a specific pintle position, such as 75%, and this commanded position should be achieved within two seconds. With the engine idling, select various pintle positions and check the actual pintle position. The pintle position should always be within 10% of the commanded position. When the linear EGR 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 the valve. Connect a digital voltmeter from the pintle position wire at the EGR valve to ground, and manually push the pintle upward. The voltmeter reading 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.