Circuit Description
The Powertrain Control Module (PCM) tests the exhaust gas recirculation
(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. |
| • | The TP angle is less than 1 percent (deceleration). |
| • | The ECT is more than 75°C (167°F). |
| • | The engine speed is between 1000 RPM and 1250 RPM. |
| • | The IAC position is steady. |
| • | MAP steady between 15 and 70 kPa |
| • | Vehicle speed is more than 40 km/h (25 mph) during
deceleration. |
| • | BARO sensor more than 70 kPa |
| • | The vehicle will need to be driven above 80 km/h (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
The MAP changes monitored during 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
Notice: If the EGR valve shows signs of excessive heat, inspect the exhaust
system for blockage--possibly a plugged converter--using the procedure
found on the Restricted Exhaust System Check. If the exhaust system is restricted,
repair the cause. Inspect for an open injector caused by one or more of the
following conditions:
| • | Grounded driver circuit |
| • | Possible faulty control module |
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 48 km/h
(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. |
Inspect for the following conditions:
| • | 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. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Reviewing the Failure Records vehicle mileage since the diagnostic
test last failed may help determine how often the condition that caused the
DTC to be set occurs. This may assist in diagnosing the condition. |
Step
| Action
| Values
| Yes
| No
|
1
| Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
| --
|
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 Failure Records data.
- Clear the DTC and monitor the 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 the scan tool Specific DTC information for DTC P0401and
note test result.
Does the scan tool indicate DTC P0401 test Ran and Passed?
| --
| System OK
|
Go to Step
2
|
