P0401

P0401-EGR SYSTEM PERFORMANCE

For complete wiring diagrams refer to Diagrams/Electrical.


Theory of Operation

This diagnostic is used to check for low EGR flow conditions. When the EGR valve is open more than 60%, the diagnostic calculates an error based on the commanded and actual EGR position. If there error is too high for a calibrated period of time, the diagnostic fails. This algorithm is not used at areas high on the torque curve. The ECM will light the MIL lamp immediately after the diagnostic runs and fails. The ECM will turn off the MIL lamp once the diagnostic runs and passes in 4 consecutive drive cycles.

- When Monitored:

Engine running, Coolant temperature above a calibrated threshold, Intake Manifold temperature above a calibrated threshold, EGR valve is open a calibratable amount.

- Set Condition:

Commanded versus actual EGR fraction differs by a calibrated threshold.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. OTHER DTCS

Ignition on, engine not running.

With the scan tool, read DTC's.

Are there any other DTCs present?

Yes

- Repair all other DTC's first.

No

- Go To 2

2. EGR LEAK

Look for visible signs (soot streaks) of an external EGR leak.

Are there any EGR leaks?

Yes

- Correct the failure.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 3

3. AIR INLET LEAK

Check for areas in the inlet air system that would allow air to be brought in after the air filter.


NOTE: During normal engine operation a hole in this area would not result in an inlet air leak.

Is there a hole in the inlet air system?

Yes

- Correct the failure.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 4

4. AIR FILTER RESTRICTION

Examine air filter minder.

Is the air filter restriction within allowable limits?

Yes

- Go To 5

No

- Replace air filter.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. BOOST LEAK

Check system for leaks.

Are there any boost air leaks?

Yes

- Correct the failure
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 6

6. EGR COOLER LEAK

Verify EGR cooler is not leaking.

Check for coolant in EGR plumbing, engine overheat fault codes, and low coolant level.

Are there signs of an EGR Cooler leak?

Yes

- Replace EGR Cooler.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 7

7. EGR COOLER FOULING

Remove the inlet and outlet EGR tubes from the EGR cooler.

Inspect the cooler for debris and plugging.

Is there excessive soot build up in the EGR cooler?

Yes

- Replace EGR Cooler.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 8

8. EGR CROSSOVER TUBE RESTRICTION

Remove EGR Crossover tube from EGR cooler and EGR valve.

Inspect tube for restriction.

Is the EGR crossover tube restricted?

Yes

- If possible clean tube. If not, replace tube.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 9

9. INTAKE AIR HEATER RESTRICTION

Remove air inlet connection and inspect intake air heaters.

Is the intake air heater restricted?

Yes

- Clean area and reassemble.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Repair complete, verify complaint is not longer present. If condition still exists return to beginning of test.