Refer to
Engine Controls Schematics
.
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 9 and 12 samples
should be sufficient for the PCM to determine adequate EGR flow and pass
the EGR test.
Conditions for Running the DTC
| • | TP, MAP, MAF, ECT, IAT, CKP sensor, VSS, injector circuit, Misfire,
Idle speed, EGR Pintle Position, DTCs are not set. |
| • | The AC status does not change. |
| • | The transaxle range does not change. |
| • | TP angle is less than 1 percent, deceleration. |
| • | Engine coolant temperature is more than 75°C (167°F). |
| • | Engine speed is between 950 RPM and 1300 RPM. |
| • | IAC position is steady. |
| • | MAP steady between 15 and 70 kPa. |
| • | Vehicle speed is more than 40 km/h (35 mph) during
deceleration. |
| • | BARO sensor more than 70 kPa. |
| • | System voltage is between 10.0 and 18.0 volts. |
| • | 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 is running, 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 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
Important: : If the EGR valve shows signs of excessive heat, inspect the exhaust
system for blockage, possibly a plugged catalytic converter, using the
Restricted Exhaust System Check
.
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:
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 |
| • | 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?
| --
|
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
Did you find and correct the condition?
| --
|
Go to Step 5
|
Go to Step 3
|
3
|
- Remove the EGR valve.
- Visually and physically inspect the following components for
excessive deposits or any kind of a restriction:
- Visually and physically inspect the EGR valve gasket and pipes
for leaks.
Did you find and correct the condition?
| --
|
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 following components for a blockage caused by excessive
deposits, casting flashing or other damage:
Did you find and correct the condition?
| --
|
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
|
