Circuit Description
The PCM tests the EGR system during deceleration by momentarily commanding the EGR valve open while monitoring the manifold absolute pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set DTC P0401. The number of test samples required to accomplish this may vary according to the amount of detected flow error.
Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows a specified number of test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test if the system is operating correctly.
Conditions for Running the DTC
| • | No Fuel Injector, CKP, TP, MAP, VSS, IAT, ECT, IAC, EGR Pintle, Misfire or MAF DTCs set. |
| • | Engine coolant temperature is more than 75°C (167°F). |
| • | RPM is between 900 and 1400 RPM. |
| • | BARO is more than 70 kPa. |
| • | Vehicle speed is more than 40 km/h (25 MPH). |
| • | A/C clutch status is unchanged. |
| • | Transmission status is unchanged. |
| • | Throttle angle is less than 1 percent |
| • | EGR position is less than 1 percent |
| • | MAP, TP, RPM and VSS are steady. |
Conditions for Setting the DTC
MAP changes monitored during the EGR flow test indicate insufficient EGR flow.
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following:
Important: If the EGR valve shows signs of excessive heat, inspect the exhaust system for blockage (possibly a plugged catalytic converter). Refer to Restricted Exhaust System Check .
To verify a repair, clear the information with the scan tool and run the EGR flow test keeping the following items in mind:
| • | The PCM will only run the EGR flow test during a gradual deceleration. |
| • | The PCM will only run the EGR test during a closed throttle condition. |
| • | The PCM will only run the EGR test at vehicle speeds more than 40 km/h (25 mph). |
| • | Several deceleration cycles will be necessary to run a sufficient number of EGR flow test samples (9-12). |
| • | If the engine speed increases more than 100 RPM from the enabling RPM (refer to Conditions for Running the DTC), the PCM will reset the test. |
| • | If the engine speed decreases more than 300 RPM from the enabling RPM (refer to Conditions for Running the DTC), the PCM will reset the test. |
| • | When the PCM commands the EGR valve open engine speed will drop. If the engine speed drops below the following RPM values, the test will not run: |
| - | Manual Transaxle - 800 RPM. |
| - | Automatic Transaxle - 700 RPM. |
| • | The EGR Test Counter displayed on the scan tool can be useful in determining that the EGR flow test is running and to keep track of the number of test samples taken. The counter will increment each time a test sample is taken. |
A Vacuum restriction to the MAP sensor - A restriction to the MAP sensor can cause the EGR flow test to fail due to insufficient MAP changes being monitored during the test. Inspect for objects blocking the vacuum to the MAP sensor. Also inspect for kinked or pinched MAP sensor vacuum hoses (if equipped.)
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
2 | Inspect the exhaust system for modification of original installed parts or leaks. Did you find and correct the condition? | -- | ||||||
3 |
Did you find and correct the condition? | -- | ||||||
4 |
Did you find and correct the condition? | -- | Go to Diagnostic Aids | |||||
5 |
Does the DTC reset? | -- | System OK |
