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 Running the DTC
| • | No Fuel Injector, CKP, TP, MAP, VSS, IAT, ECT, IAC, EGR Pintle,
Misfire or MAF DTC(s) set. |
| • | Engine coolant temperature is greater than 75°C (167°F). |
| • | RPM is between 1000 and 1400 RPM. |
| • | MAP value is between 10 and 50 kPa. |
| • | BARO is greater than 0 kPa. |
| • | Vehicle speed is greater than 40 km/h (25 MPH). |
| • | A/C clutch status is unchanged. |
| • | Transmission status is unchanged. |
| • | Throttle angle is less than 1% |
| • | EGR position is less than 1% |
| • | MAP, TP, RPM and VSS are steady. |
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 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 MIL 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. |
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 RPM. |
| • | 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: |
| - | 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 Freeze Frame/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
| Did you perform the Powertrain
On-Board Diagnostic (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.
Did you find and correct the condition?
| --
|
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. |
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. Refer to
Exhaust Gas Recirculation Valve Replacement
- Inspect the manifold EGR ports and the EGR inlet and outlet pipes
for a blockage caused by excessive deposits or other damage.
Did you find and correct the condition?
| --
|
Go to Step 5
| Go to Diagnostic Aids
|
5
|
- Use the scan tool in order to record the Fail Records and clear
DTCs.
- With a scan tool, observe the EGR Test Count parameter.
- Operate the vehicle as specified in Diagnostic Aids.
- Continue operating the vehicle until 9 -12 EGR Test Count test
samples have been taken.
Does the DTC reset?
| --
|
Go to Step
2
| System OK
|
