Circuit Description
The powertrain control module (PCM) tests the exhaust gas recirculation
(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 15
test samples during the first ignition cycle following a scan tool Clear
Info or a battery disconnect. Between six and nine 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
• | The following sensor diagnostic trouble codes (DTCs) are not set: |
- | Vehicle speed sensor (VSS) |
- | Throttle position (TP) sensor |
- | Intake air temperature (IAT) sensor |
- | Engine coolant temperature (ECT) sensor |
- | Crankshaft position (CKP) sensor |
- | Mass air flow (MAF) sensor |
• | The BARO is more than 77 kPa. |
• | The engine coolant temperature is more than 80°C (176°F). |
• | The engine speed is between 900-1,300 RPM. |
• | The vehicle speed is more than 36.21 km/h (22.5 mph). |
• | The throttle is closed. |
• | The EGR pintle position less than 1 percent (valve closed) |
• | The idle air control (IAC) position, the MAP, the engine RPM and
the vehicle speed are steady |
• | The A/C clutch state and the transmission state are unchanged |
Conditions for Setting the DTC
The MAP changes monitored during the EGR flow test indicate insufficient
EGR flow.
Action Taken When the DTC Sets
• | The PCM illuminates the malfunction indicator lamp (MIL) when
the diagnostic runs and fails. |
• | The PCM records the operating conditions at the time the diagnostic
fails. The PCM stores this information in the Freeze Frame and/or Failure
Records. |
Conditions for Clearing the MIL/DTC
• | The PCM turns the MIL OFF after 3 consecutive
drive trips during which the diagnostic runs and passes. |
• | A last test failed, or the current DTC, clears when the diagnostic
runs and passes. |
• | A History DTC clears after 40 consecutive warm-up cycles, if
no other emission related diagnostic failures are reported. |
• | Use a scan tool in order to clear the MIL diagnostic trouble code. |
• | Interrupting the PCM battery voltage may or may not clear DTCs.
This practice is not recommended. Refer to
Powertrain Control Module Description
, Clearing Diagnostic
Trouble Codes. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• | The PCM harness connectors |
• | The electrical center fuse/relay cavities |
• | The component terminals |
• | The component harness connector |
Using this kit will prevent damage caused by the improper probing of
connector terminals.
Important: If the EGR valve shows signs of excessive heat, check the exhaust system
for blockage, possibly a plugged catalytic converter. Refer to 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 36.21 km/h
(22.5 mph). |
• | Several deceleration cycles will be necessary to run a sufficient
number of EGR flow test samples (6-9). |
• | The EGR Flow 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 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. Check for objects blocking the
vacuum to the MAP sensor.
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.
If the problem is intermittent, refer to
Intermittent Conditions
.
Step
| Action
| Value(s)
| 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 problem found and corrected?
| --
|
Go to Step 5
|
Go to Step 3
|
3
|
- Remove the EGR valve. Refer to
Exhaust Gas Recirculation Valve Replacement
.
- 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 |
- If a problem is found, clean or replace EGR system components
as necessary. Refer to
Exhaust Gas Recirculation (EGR) System Cleaning
.
Was a problem found and corrected?
| --
|
Go to Step 5
|
Go to Step 4
|
4
|
- Remove the EGR inlet and outlet pipes from the exhaust manifold
and the intake manifold. Refer to
Exhaust Gas Recirculation Pipe Replacement
.
- Inspect the crossover assembly and the EGR inlet and outlet pipes
for a blockage caused by excessive deposits or other damage.
Refer to
Exhaust Gas Recirculation (EGR) System Cleaning
.
- If a problem is found, correct the condition as necessary.
Was a problem found and corrected?
| --
|
Go to Step 5
| Go to Diagnostic
Aids
|
5
|
- Review and record the scan tool Failure Records data.
- Clear DTC and monitor EGR Test Count display on the scan tool
while operating the vehicle as specified in DTC P0401 Diagnostic
Aids.
- Continue operating the vehicle until 9-12 test samples have
been taken.
- Select scan tool Specific DTC information for DTC P0401.
Does the scan tool indicate DTC P0401 test ran and passed?
| --
|
Go to Step 6
|
Go to Step 2
|
6
| Review Captured Info using the
scan tool.
Are there any DTCs that have not been diagnosed?
| --
| Go to the applicable DTC table
| System OK
|