For 1990-2009 cars

### 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 Setting the DTC

Manual Transaxle

• | No TP sensor, VSS, Misfire, IAT sensor, MAP sensor, Idle speed, EGR Pintle, Fuel injector, CKP sensor, ECT sensor, or MAF sensor DTCs set.

• | System voltage is between 10 and 16 volts.

• | BARO:

- | Manual Transaxle - BARO is greater than 70 kPa.

- | Automatic Transaxle - BARO is greater than 65 kPa.

• | Engine Speed:

- | Manual Transaxle - Engine speed is between 1000 RPM and 1400 RPM.

- | Automatic Transaxle - Engine speed is between 1050 RPM and 1400 RPM.

• | Intake air temperature is greater than 80°C (176°F).

• | Engine coolant temperature is greater than 75°C (167°F).

• | IAC position is steady.

• | Vehicle speed is greater than 40 km/h (25 MPH).

• | The throttle is closed.

• | MAP changes monitored during the EGR flow test indicate insufficient EGR flow.

### Action Taken When the DTC Sets

• | The PCM will illuminate the 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 Fail Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been 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 the scan tool Clear Information function or by disconnecting the PCM battery feed.

### Diagnostic Aids

Important: If the EGR valve shows signs of excessive heat, check 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 greater 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.

• | 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.

Check for the following conditions:

• | 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. Check for objects blocking the vacuum to the MAP sensor. Also check for kinked or pinched MAP sensor vacuum hoses (if equipped.)

• | Poor connection at the PCM - Inspect harness connectors for the following conditions:

- | Backed out terminals.

- | Improper mating.

- | Broken locks.

- | Improperly formed or damaged terminals.

- | Poor terminal to wire connection.

• | Poor connection or damaged harness - Inspect the wiring harness for damage.

• | If the harness appears to be OK, observe the Actual EGR Position display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display will indicate the location of the fault.

Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.

#### DTC P0401 - EGR System Flow Insufficient

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Inspect the exhaust system for modification of original installed parts or leaks.
2. If a problem was found, repair exhaust system as necessary.

Was a problem found?

--

Go to Step 5

Go to Step 3

3 |

1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
2. Visually and physically inspect the following items:

• | The pintle, the valve passages and the adapter for excessive deposits or any kind of a restriction.

• | the EGR valve gasket and pipes for leaks.

3. If a problem is found, clean or replace EGR system components as necessary.

Was a problem found?

--

Go to Step 5

Go to Step 4

4 |

1. Remove the EGR inlet and outlet pipes from the exhaust manifold and the intake manifold. Refer to Exhaust Gas Recirculation Valve Replacement
2. Inspect the manifold EGR ports and the EGR inlet and outlet pipes for a blockage caused by excessive deposits or other damage.
3. If a problem is found, correct the condition as necessary.

Was a problem found?

--

Go to Step 5

Go to Diagnostic Aids

5 |

1. Review and record the scan tool Fail Records data.
2. Clear DTC and monitor EGR Test Count display on the scan tool while operating the vehicle as specified in DTC P0401 Diagnostic Aids.
3. Continue operating the vehicle until 9 -12 EGR Test Count test samples have been taken.
4. Select scan tool Specific DTC information for DTC P0401.

Does scan tool indicate DTC P0401 Test Ran and Passed?

--

System OK

Go to Step 2