GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Exhaust Gas Recirculation (EGR) System Diagnosis

Object Number: 394339 Size: LF
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OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

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.

Diagnostic Aids

Intermiitent conditions can be cause by wiring problems.

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 check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis 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 greater than 0%.

    2.

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

    3.

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

    4.

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

EGR System Check With Linear EGR Valve

Step

Action

Value(s)

Yes

No

1

Important:: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

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 normal operating temperature is reached.
  4. 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

3

  1. Turn On the ignition leaving the engine OFF.
  2. 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

4

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

5

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

Is the test lamp ON?

--

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 EGR valve feed control circuit and the EGR valve ground circuit at the EGR valve harness connector.
  3. 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

7
  1. Turn OFF the ignition.
  2. 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

8

Check the EGR valve feed control circuit 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:

    • Short to voltage
    • An open
    • 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 valve 5 volt 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

11
  1. Turn OFF the ignition.
  2. Probe the EGR valve 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

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 valve 5 volt 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

14
  1. Disconnect the EGR valve harness connector.
  2. Install a jumper between the EGR valve 5 volt reference circuit and the EGR valve pintle position signal circuit 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 EGR valve feed control circuit 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 EGR pintle position signal circuit 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 MAP sensor reading.
  3. Command ON the EGR valve to the specified value.
  4. Observe the MAP sensor reading.

Does the MAP sensor reading go higher?

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 EGR pintle position signal 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
  1. Replace the VCM.
  2. Program the new VCM. Refer to VCM Replacement/Programming .
  3. Perform the Passlock Reprogramming Procedure. Refer to PASSLOCK Reprogramming Seed and Key in Theft Deterrent.
  4. Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

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 normal operating temperature is reached.
  4. Command ON and OFF the EGR valve using the scan tool.

Does the actual EGR position follow the commanded EGR position?

--

System OK

Go to Step 2