EGR Function Testing - General Motors Trucks GMC Cab & Chassis V3500

Ported & Backpressure EGR

1. Install vacuum gauge between EGR valve and carburetor vacuum port. With engine at normal operating temperature, increase engine speed to about 3000 RPM. Vacuum gauge should read at least 5 in. Hg.
2. Check EGR Thermal Vacuum Switch (TVS) operation by installing a vacuum gauge between TVS and vacuum source and noting presence of vacuum with engine running and at normal operating temperature.
3. Turn engine off. Manually depress/push in EGR valve diaphragm. While depressed, hold finger over source tube and release diaphragm. Check for diaphragm and seat movement. Diaphragm should take at least 20 seconds to move to seated position. If not, replace EGR valve.
4. Start engine. Using a hand-held vacuum pump, apply vacuum to EGR valve. EGR valve should open and engine should run rough or stall. If EGR valve does not open, replace EGR valve. If EGR valve opened, but idle quality did not change, clean plugged EGR ports.

Linear EGR

1. Install scan tool. Ensure P/N switch is operating properly. With engine at normal operating temperature, command EGR pintle position to zero percent. Increase engine speed to 2000 RPM. If scan tool reads actual EGR pintle position at greater than 3 percent, EGR valve is stuck open. Replace EGR valve.
2. If scan tool reads actual EGR pintle position at 3 percent or less, command a 25 percent position step increase (i.e., 0-25 percent, 25-50 percent, 50-75 percent, etc.). Observe MAP sensor reading and actual EGR pintle position for 3 seconds. EGR should increase by about 25 percent and MAP reading should also increase.
3. If actual EGR pintle position is stable and within 10 percent position of desired EGR pintle position command after 2 seconds, go to next step. If actual EGR pintle position is not as specified, go to step 5 .
4. MAP reading should have increased when EGR pintle responded. If MAP did not respond, check EGR passages and EGR valve for blockage. If MAP responded, set desired EGR pintle position to 100 percent. If EGR pintle position sets to 100 percent, EGR is okay. If not, replace EGR valve.
5. Turn engine off. Check EGR electrical circuit and connecting components. Turn ignition on, check 5-volt reference voltage on harness connector terminal "D" (Gray wire). If 5-volt reference voltage is not present, check ECM. If circuits are okay, replace EGR valve.

TEST 3

1. Install scan tool. Ensure transmission range switch is operating properly. With engine at normal operating temperature, command EGR pintle position to zero percent. Increase engine speed to 2000 RPM. If scan tool reads actual EGR pintle position at greater than 3 percent, EGR valve is stuck open. Replace EGR valve.
2. If scan tool reads actual EGR pintle position at 3 percent or less, command a 25 percent position step increase (i.e. 0-25 percent, 25-50 percent, 50-75 percent, etc.). Observe MAP reading and actual EGR pintle position for 3 seconds. EGR should increase by about 25 percent position and MAP reading should also increase.
3. If actual EGR pintle position is stable and within 10 percent of desired EGR pintle position command after 2 seconds, go to next step. If actual EGR pintle position is not as specified, go to step 5).
4. MAP reading should have increased when EGR pintle responded. If MAP did not respond, check EGR passages and EGR valve for blockage. If MAP responded, set desired EGR pintle position to 100 percent. If EGR pintle position sets to 100 percent, EGR is okay. If not, replace EGR valve.
5. Turn engine off. Check EGR electrical circuit and connecting components. Turn ignition on, check for 5-volt reference voltage on harness connector terminal "D" (Gray wire). If 5-volt reference voltage is not present, check PCM/VCM. If circuits are okay, replace EGR valve.

TEST 4

For EGR function testing, see appropriate ENGINE PERFORMANCE section of electronic information product.