P0401

P0401-EGR SYSTEM PERFORMANCE





For a complete wiring diagram Consult Diagrams/Electrical.

Theory of Operation

Exhaust gas recirculation is a method of reducing emissions of oxides of nitrogen. As the inert exhaust gas is recirculated, the mixture absorbs heat in the combustion chamber without interacting with the fuel/air mixture and reduces the formation of NOx emissions. After the EGR monitor conditions are met, the EGR valve is turned on and off momentarily. The EGR monitor calculated the difference in engine roughness from the EGR off condition to the EGR condition. This engine combustion stability difference as measured by engine roughness is the measure of a functional EGR system.

- When Monitored:
Engine running for greater than two minutes with the Engine Coolant Temp greater than 70° C (158° F). EGR active. Less than 8500 feet. Ambient temperature greater than -6° C (20° F).

- Set Condition:
The PCM closes the EGR valve while monitoring the O2 Sensor signal. Once a closed EGR fueling sample has been established the PCM then ramps in EGR and additional fueling while monitoring the O2 sensor signal in the open state. A fueling sample is again established. The PCM then compares the different O2 Sensor signal readings (fueling samples). If a larger than expected variation is detected, a soft failure is recorded. Three soft failures set a one trip failure. After two failed trips, a DTC is set and the MIL is illuminated.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.Initial Inspection and Diagnostic Overview

Diagnostic Test

1. DTC IS ACTIVE

NOTE: Diagnose and repair any EGR circuit DTCs before continuing with this procedure.

Turn the ignition on.
With the scan tool, select View DTCs. Copy DTC and Freeze Frame information.
Start the engine and allow it to reach operating temperature.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

NOTE: Attempt to operate the vehicle under conditions similar to which the DTC was set.

NOTE: It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to set.

With a scan tool, select View DTCs.
Is the DTC Active or Pending at this time?

Yes

- Go to 2

No

- Refer to the CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. Checking For An Intermittent DTC

2. ROUGH IDLE OR STALLING AT IDLE
Turn the ignition off.
Turn all accessories off.
Start the engine.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Does the engine run rough or stall at idle?

Yes

- Go to 3

No

- Go to 5

3. EGR VALVE ASSEMBLY CONTROL CIRCUIT
Turn the ignition off.
Disconnect the EGR Valve Assembly harness connector.
Start the engine.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Does the engine continue to run rough or stall with the EGR Valve Assembly connector disconnected?

Yes

- Go to 8

No

- Go to 4

4. (K35) EGR CONTROL CIRCUIT SHORTED TO VOLTAGE




Turn the ignition off.
Disconnect the C1 and C2 Powertrain Control Module (PCM) connectors.
Turn the ignition on.
Measure the voltage of the (K35) EGR Control circuit in the EGR Valve Assembly harness connector.
Is there any voltage present?

Yes

- Repair the short to voltage in the (K35) EGR Control circuit.
- Perform the PCM Verification Test. Powertrain Verification Test

No

- Go to 9

5. EGR SYSTEM TEST
Turn all accessories off.
Start the engine and allow it to reach operating temperature.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

With the scan tool, perform the EGR System Test.
Select OPEN to open the EGR valve.
Did the engine run rough or stall when the valve was opened during the system test?

Yes

- Go to 8

No

- Go to 6

6. (Z902) GROUND CIRCUIT OPEN OR HIGH RESISTANCE




Turn the ignition off.
Using a 12 volt test light connected to the 12 volts, check the (Z902) Ground circuit in the EGR Valve Assembly harness connector.

NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.

Is the test light illuminated and bright?

Yes

- Go to 7

No

- Repair the excessive resistance in the (Z902) Ground circuit.
- Perform the PCM Verification Test. Powertrain Verification Test

7. (K35) EGR CONTROL CIRCUIT HIGH RESISTANCE
Turn the ignition off.
Connect the EGR Valve Assembly connector.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 along with the #8815-1 to perform the diagnosis.

Using a voltmeter, perform a voltage drop test by backprobing the (K35) EGR Control circuit at the EGR Valve Assembly harness connector and probing the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.
Start the engine and allow it to reach operating temperature.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

With the scan tool, perform the EGR System Test.
Select OPEN to open the EGR valve.
Monitor the circuit voltage on the voltmeter.
Is the voltage below 0.5 volts when the valve was opened during the system test?

Yes

- Go to 8

No

- Repair the excessive resistance in the (K35) EGR Control circuit.
- Perform the PCM Verification Test. Powertrain Verification Test

8. EGR VALVE ASSEMBLY
WARNING: The normal operating temperature of the EGR system is very high. Never work around or attempt to service any part of the EGR system until it has cooled.

Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the EGR Valve Assembly and the Powertrain Control Module (PCM).
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Search for any Technical Service Bulletins that may apply.
Inspect the EGR Valve Assembly for the following:
- Proper mounting, leaking gasket(s)
- Damaged, leaking, or obstructed EGR tube(s)
- Carbon build up on or near the EGR pintle or within passages.
Were any problem found?

Yes

- Repair or replace the EGR system components as necessary.
- Perform the PCM Verification Test. Powertrain Verification Test

No

- Replace the EGR Valve Assembly.
- Perform the PCM Verification Test. Powertrain Verification Test

9. POWERTRAIN CONTROL MODULE (PCM)
Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the EGR Valve Assembly and the Powertrain Control Module (PCM).
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Verify that there is good pin to terminal contact in the Solenoid and the Powertrain Control Module connectors.
Search for any Technical Service Bulletins that may apply.
Were any problems found?

Yes

- Repair as necessary.
- Perform the PCM Verification Test. Powertrain Verification Test

No

- Replace and program the Powertrain Control Module (PCM).
- Perform the PCM Verification Test. Powertrain Verification Test