Exhaust Gas Recirculation (EGR) System Diagnosis. GMC Truck GMC P42 Commercial Chassis 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 Exhaust Gas Recirculation (EGR) System Diagnosis

EGR/ECT/CKP - Comp Loc Figure
Engine Controls (Cell 21: Engine Data Sensors 3)
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

In order to control the Exhaust Gas Recirculation (EGR), the control module operates the linear EGR valve. The linear EGR valve is a small motor with a pintle that is normally closed. By providing a ground path, the control module will open the pintle and allow the exhaust gasses to pass through the valve. The control module of the EGR is based on the following inputs:

•	The engine coolant temperature - above 25°C.

•	The TP OFF idle

•

MAP

•

BARO

•	Park/Neutral position

•	The pintle position sensor.

This chart is used for a malfunctioning valve, plugged EGR passages, or improper wiring connections.

Test Description

The numbers below refer to the step numbers in the diagnostic table.

At idle, the EGR valve should not be open greater than 0%.

This step checks the ability of the pintle to be manually commanded to the desired positions.

This step checks the electrical circuit for a short to voltage.

This step checks the electrical control circuits from the VCM to the EGR valve.

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Set the parking brake and block the drive wheels.
Install the scan tool.
Idle the engine until normal operating temperature is reached.
Check the actual EGR position with the scan tool .

Does the scan tool indicate more than the specified value?

0 %

Go to Step 4

Go to Step 3

Turn ON the ignition leaving the engine OFF.
Command ON the EGR valve to the specified value using the scan tool.

Does the actual EGR position follow the commanded EGR position?

100 %

Go to Step 17

Go to Step 6

Disconnect the EGR valve harness connector.

Does the scan tool indicate the actual EGR position above the specified value?

0 %

Go to Step 16

Go to Step 5

Turn OFF the ignition.
Connect a test lamp between the EGR valve feed control circuit and the EGR valve ground circuit at the EGR harness connector.
Turn ON the ignition leaving the engine OFF.

Is the test lamp ON?

Go to Step 15

Go to Step 10

Turn ON the ignition leaving the engine OFF.
Connect a test lamp between the EGR valve feed control circuit and the EGR valve ground circuit at the EGR harness connector.
Command ON the EGR valve using the scan tool to the specified value.

Is the test lamp ON?

100 %

Go to Step 13

Go to Step 7

Turn OFF the ignition .
Probe the EGR valve ground circuit with a test lamp connected to B+.

Is the test lamp ON?

Go to Step 8

Go to Step 9

Check the EGR valve feed control circuit for an open.

Did you find a problem?

Go to Step 22

Go to Step 21

Check the EGR valve ground circuit for the following conditions:

•	Short to voltage

•

An open

•	Excessive resistance

Did you find a problem?

Go to Step 22

Go to Step 11

Turn ON the ignition leaving the engine OFF.
Probe the EGR 5 V reference circuit at the EGR valve harness connector with a J 39200 DMM connected to a ground.

Is the voltage above the specified value?

5.2 V

Go to Step 22

Go to Step 11

Turn OFF the ignition.
Probe the EGR sensor ground circuit at the EGR valve harness connector with a test lamp connected to B+.

Is the test lamp ON?

Go to Step 19

Go to Step 12

Turn OFF the ignition.
Disconnect the VCM C4 connector.
Check the EGR sensor ground circuit for an open.

Did you find a problem?

Go to Step 22

Go to Step 21

Turn ON the ignition leaving the engine OFF.
Probe the EGR 5 V reference circuit at the EGR valve harness connector with a J 39200 DMM connected to a ground.

Is the voltage near the specified value?

5.2 V

Go to Step 14

Go to Step 22

Disconnect the EGR valve harness connector.
Install a jumper between the 5 V reference circuit and the EGR pintle position signal circuit at the EGR valve harness connector.
Turn the ignition ON leaving the engine OFF.

Is the actual EGR position near the specified value?

100

Go to Step 19

Go to Step 20

Disconnect the VCM C4 connector.
Turn the ignition ON leaving the engine OFF.
Check the EGR valve feed control circuit for a short to voltage.

Did you find a problem?

Go to Step 22

Go to Step 23

Disconnect the VCM C2 connector.
Turn the ignition ON leaving the engine OFF.
Check the EGR pintle position signal circuit for a short to voltage.

Did you find a problem?

Go to Step 22

Go to Step 23

Start the engine.
Observe the MAP sensor reading.
Command ON the EGR valve to the specified value.
Observe the MAP sensor reading.

Does the MAP sensor reading go higher?

30 %

Go to Step 24

Go to Step 18

Repair the blockage in the EGR valve passages.

Is the action complete

Go to Step 24

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .

Is the action complete?

Go to Step 24

Check the EGR pintle position circuit for an open.

Did you find a problem?

Go to Step 22

Go to Step 21

Check for a poor connection at the VCM connectors.

Did you find a problem?

Go to Step 22

Go to Step 23

Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 24

Replace the VCM.
Program the VCM. Refer to VCM Replacement/Programming .
Perform the Crankshaft Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

Is the action complete?

Go to Step 24

Set the parking brake and block the drive wheels.
Install the scan tool.
Idle the engine until normal operating temperature is reached.
Command ON and OFF the EGR using the scan tool .

Does the actual EGR position follow the commanded EGR position?

System OK

Go to Step 2