Circuit Description
The PCM tests the EGR system during deceleration by momentarily commanding
the EGR valve to 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 twelve
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.
Conditions for Running the DTC
| • | No TP, MAP, MAF, ECT, IAT, CKP sensor, VSS, injector circuit,
Misfire, Idle speed, EGR Pintle Position, DTCs set. |
| • | The AC status does not change. |
| • | The transaxle range does not change. |
| • | TP angle is less than 1% (deceleration). |
| • | Engine coolant temperature is greater than 75°C (167°F). |
| • | Engine speed is between 1000 RPM and 1250 RPM. |
| • | IAC position is steady. |
| • | MAP steady between 15 and 70 kPa. |
| • | System voltage is between 10.0 and 18.0 volts. |
| • | Vehicle speed is greater than 25 mph during deceleration. |
| • | BARO sensor greater than 70 kPa. |
| • | The vehicle will need to be driven above 50 mph, and then
allowed to decelerate. When the vehicle is decelerating while meeting all
of the criteria listed above, the PCM will enable the test to run.
When the test runs, you will see the Desired EGR parameter and the
Actual EGR position on the scan tool change from 0 to a calibrated
value above 0. |
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 runs and fails. |
| • | If equipped with traction control, the PCM will command the EBTCM
via the serial data circuit to turn OFF traction control and illuminate
the TRACTION OFF lamp. |
| • | The PCM will store conditions which were present when the DTC
set as Freeze Frame/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
To verify a repair, clear info 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 above 30 mph. |
| • | Several deceleration cycles will be necessary to run a sufficient
number of EGR flow test samples (9-12). |
| • | 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:
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.
| • | Poor terminal connection. |
| | Inspect the harness connectors for backed out terminals, improper mating,
broken locks, improperly formed or damaged terminals, and faulty terminal
to wire connection. Use a corresponding mating terminal to test for proper
tension. Refer to
Intermittents and Poor Connections Diagnosis
, and
Connector Repairs
Wiring Systems. |
| | Inspect the wiring harness for damage. If the harness appears to be
OK, observe the sensor display on the scan tool while moving connectors and
wiring harnesses related to the sensor. A change in the sensor display
may indicate the location of the fault. Refer to
Wiring Repairs
in Wiring Systems. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Fail Records
can be useful in determining when the DTC was last set.
Step
| Action
| Value(s)
| Yes
| No
|
1
| Was the Powertrain OBD System Check performed?
| --
|
Go to Step 2
| Go to
Powertrain On Board Diagnostic (OBD) System Check
|
2
|
- Inspect the exhaust system for modification of original installed
parts or leaks.
- If a problem was found, repair exhaust system as necessary.
Was a condition present that required repair?
| --
|
Go to Step 5
|
Go to Step 3
|
3
|
- Remove the EGR valve.
- Visually and physically inspect the following items:
| • | Pintle, valve passages and the adapter for excessive deposits
or any kind of a restriction. |
| • | EGR valve gasket and pipes for leaks. |
- If a problem is found, clean or replace EGR system components
as necessary.
Was a condition present that required repair?
| --
|
Go to Step 5
|
Go to Step 4
|
4
|
- Remove the EGR inlet and outlet pipes from the exhaust manifold
and the intake manifold.
- Inspect the manifold EGR ports and the EGR inlet and outlet pipes
for a blockage caused by excessive deposits, casting flashing or other damage.
- If a problem is found, correct the condition as necessary.
Was a condition present that required repair?
| --
|
Go to Step 5
| Go to Diagnostic Aids
|
5
|
- Review and record the scan tool Fail Records data.
- Clear DTC and monitor EGR Test Count display on the scan tool
while operating the vehicle as specified in Diagnostic Aids.
- Continue operating the vehicle EGR Test Count until 9 -
12 test samples have been taken.
- Select scan tool Specific DTC information for DTC P0401.
- Note test result.
Does scan tool indicate DTC P0401 Test Ran and Passed?
| --
| System OK
|
Go to Step
2
|
