GM Service Manual Online
For 1990-2009 cars only

Object Number: 627700  Size: MF
Engine Controls Components
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Sensor Controls: MAF, EGR, and EVAP Controls

Circuit Description

An exhaust gas recirculation (EGR) system is used in order to lower oxides of nitrogen (NOx) emission levels caused by high combustion temperatures. The EGR accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, combustion temperatures are reduced.

A linear EGR valve is used on this system. The linear EGR valve is designed in order to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The valve controls exhaust flow going into the intake manifold from the exhaust manifold through an orifice with a control module controlled pintle valve. The control module commands the EGR by applying a 12 volt duty cycle to the EGR valve. This can be monitored on a scan tool as desired EGR position.

The control module can monitor the pintle position with the EGR pintle position signal. This sensor uses a variable resistor with a 5 volt reference, a signal circuit, and a ground. The signal circuit monitors changes in voltage on the variable resistor as the pintle moves.

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

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

  1. At idle, the EGR valve should not be open more than 0 percent.

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

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

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

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Set the parking brake and block the drive wheels.
  2. Install the scan tool.
  3. Idle the engine until ther engine reaches a normal operating temperature.
  4. Check the actual EGR position with the scan tool.

Is the EGR Position more than the specified value?

0%

Go to Step 4

Go to Step 3

3

  1. Turn ON the ignition, leaving the engine OFF.
  2. Command the EGR valve ON 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

4

Disconnect the EGR valve harness connector.

Does the scan tool indicate the actual EGR position is more than the specified value?

0%

Go to Step 16

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Connect a test lamp between the feed control circuit of the EGR valveand the EGR valve ground circuit at the EGR harness connector.
  3. Turn ON the ignition, leaving the engine OFF.

Does the test lamp illuminate?

--

Go to Step 15

Go to Step 10

6

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

Does the test lamp illuminate?

100%

Go to Step 13

Go to Step 7

7

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

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 9

8

Check the feed control circuit to the EGR valve for an open.

Did you find a problem?

--

Go to Step 22

Go to Step 21

9

Check the EGR valve ground circuit for the following conditions:

    • A short to voltage
    • An open
    • An excessive resistance

Did you find a problem?

--

Go to Step 22

Go to Step 21

10

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

Is the voltage more than the specified value?

5.2 V

Go to Step 22

Go to Step 11

11

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

Does the test lamp illuminate?

--

Go to Step 19

Go to Step 12

12

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

Did you find a problem?

--

Go to Step 22

Go to Step 21

13

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

Is the voltage near the specified value?

5.2 V

Go to Step 14

Go to Step 22

14

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

Is the actual EGR position near the specified value?

100%

Go to Step 19

Go to Step 20

15

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

Did you find a problem?

--

Go to Step 22

Go to Step 23

16

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

Did you find a problem?

--

Go to Step 22

Go to Step 23

17

  1. Start the engine.
  2. Observe the manifold absolute pressure (MAP) sensor reading.
  3. Command the EGR valve ON to the specified value.
  4. Observe the MAP sensor reading.

Did the MAP sensor reading increase?

30%

Go to Step 24

Go to Step 18

18

Repair the blockage in the EGR valve passages.

Is the action complete?

--

Go to Step 24

--

19

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

Is the action complete?

--

Go to Step 24

--

20

Check the pintle position circuit for an open or a short to ground.

Did you find a problem?

--

Go to Step 22

Go to Step 21

21

Check for a poor connection at the VCM connectors.

Did you find a problem?

--

Go to Step 22

Go to Step 23

22

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

Is the action complete?

--

Go to Step 24

--

23

Important: The replacement VCM must be programmed.

Replace the VCM. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 24

--

24

  1. Set the parking brake and block the drive wheels.
  2. Install the scan tool.
  3. Idle the engine until the engine reaches a normal operating temperature.
  4. Command the EGR ON and OFF using the scan tool.

Does the actual EGR position follow the commanded EGR position?

--

System OK

Go to Step 2