GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1997 🢒 S/T Isuzu - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Exhaust Gas Recirculation (EGR) System Diagnosis

Exhaust Gas Recirculation (EGR) System Diagnosis Overview

Results Of Incorrect Operation

With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:

    • The engine stalls after a cold start.
    • The engine stalls at idle after deceleration.
    • The vehicle surges during cruise.
    • The vehicle idles roughly.

If the EGR valve stays open all of the time, the engine may not idle. A DTC P0401 may set. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .

Too little or no EGR flow allows the combustion temperatures to get too high during acceleration and load conditions. This could cause the following conditions:

    • Spark knock (detonation)
    • Engine overheating
    • DTC P0401

System Check

The Linear EGR System Check covers the diagnosis of the EGR system. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .

Exhaust Gas Recirculation (EGR) System Diagnosis Linear System Check

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.

If DTC P0401 or P1406 is stored, refer to the applicable DTC table. 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.

  1. At idle, the EGR valve should not be open greater than 3%. A faulty malfunctioning park/neutral position Trans Range (TR) position pressure switch or the EGR valve stuck open will allow exhaust gases to enter the combustion chamber and create a rough idle condition.

    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 of the EGR valve and connecting components.

    4.

  4. This step checks for plugged EGR passages or a damaged 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.
  2. Block the drive wheels.
  3. Install a scan tool.
  4. Check the PRNDL position
  5. Allow the engine to idle at the normal operating temperature.
  6. Use a scan tool in order to command the EGR pintle position to the specified value.
  7. Increase the RPM to the specified value.

Is the actual EGR pintle position greater than the specified value?

0%

2000

3%

Go to Step 15

Go to Step 3

3
  1. Use a scan tool in order to command a 25% position step increase (0-25%, 25-50%, 50-75%, 75-100%).
  2. Observe the MAP and the actual EGR pintle position for the specified value. The EGR should increase by about 25% of the position, and the MAP should also increase.

Is the actual EGR pintle position stable, and within 10% of position of the desired EGR pintle position command after the specified value?

3 seconds

2 seconds

Go to Step 4

Go to Step 6

4

Set the EGR pintle position to the specified value.

Did the MAP increase when the actual pintle responded?

25%

Go to Step 5

Go to Step 13

5

Set the desired EGR pintle position to the specified value.

Is the desired EGR pintle position at the specified value?

100%

--

Go to Step 14

6
  1. Check the fuse.
  2. Replace the fuse if necessary.

Is the action complete?

--

Go to Step 16

Go to Step 7

7
  1. Check for any open circuits in the wiring to the EGR valve coil.
  2. Repair if necessary. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 16

Go to Step 8

8
  1. Check for any poor connections to the EGR valve coil.
  2. Repair if necessary. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 16

Go to Step 9

9
  1. Connect the J 39200 DVM.
  2. Check for the reference voltage at the EGR valve.

Is the voltage at the specified value?

5V

Go to Step 10

Go to Step 11

10
  1. Turn the ignition ON with the engine OFF.
  2. Remove the EGR valve, leaving the connector ON.
  3. Push in the pintle of EGR valve.

    4. Hold in the pintle of the EGR valve.

  4. Check for the voltage at the position sensor signal from the valve.

Is there any voltage present?

--

Go to Step 11

Go to Step 14

11
  1. Check for an open in the circuit from the control module to the EGR valve in the pintle position circuit.
  2. Repair if necessary. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 16

Go to Step 12

12

Replace the control module. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 16

--

13
  1. Check the EGR valve passages for blockages.
  2. Repair if necessary.

Is the action complete?

--

Go to Step 16

--

14

Replace the EGR valve. Refer to EGR Valve Replacement .

Is the action complete?

--

Go to Step 16

--

15
  1. The EGR valve is stuck open.
  2. Replace the EGR valve. Refer to EGR Valve Replacement .

Is the action complete?

--

Go to Step 16

--

16
  1. Turn the ignition ON with the engine OFF.
  2. Use a scan tool in order to command the component ON and OFF.

Does the component operate properly?

--

System OK

Go to Step 1