Circuit Description
The powertrain control module (PCM) controls the movement of the exhaust
gas recirculation (EGR) valve using the EGR control circuit. The control circuit
consists of the PCM ignition feed, the EGR solenoid, and the ground circuit.
The PCM uses the pintle position sensor to make sure that the valve responds
properly to the commands from the PCM.
The PCM tests the EGR valve to make sure that the proper amount of exhaust
gas flows into the engine. During a deceleration, the PCM commands the EGR
valve open. The PCM looks for an increase in manifold absolute pressure
(MAP) when the valve opens. If the PCM detects a less than expected increase
in MAP, the PCM makes note of the error amount, and adjusts the internal
fail counter towards the fail threshold. When the internal fail counter
exceeds the calibrated fail threshold, the PCM will set DTC P0401.
The number of test samples required for the fail counter to exceed the fail
threshold may vary based on the amount of error.
Normally, the PCM will only allow one EGR flow test sample per ignition
cycle. However, the PCM will allow fifteen test samples on the first ignition
cycle after a scan tool Clear DTC Information function. This helps to quickly
verify an EGR system repair. The PCM should be able to decide if the system
is working correctly within five to fifteen test samples.
Conditions for Running the DTC
| • | No TP sensor, MAP sensor, VSS, ECT sensor, IAC sensor, EGR Pintle
Position, DTCs are set. |
| • | System voltage is between 11-18 volts. |
| • | Engine speed is between 700-1200 RPM. |
| • | ECT between 80°C (176°F) and 110°C (230°F). |
| • | Vehicle speed is more than 23 mph. |
| • | BARO is more than 70 kPa. |
| • | Throttle is steady below 2 percent . |
| • | The transaxle is steady. |
| • | The torque converter clutch (TCC) is steady. |
| • | The A/C compressor clutch is steady. |
| • | IAT is less than 50° C (122°F). |
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 illuminates the malfunction indicator lamp (MIL) during
the second consecutive trip in which the diagnostic test runs and fails. |
| • | The PCM stores the conditions present when the DTC set as Freeze
Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after the third consecutive trip
in which the diagnostic runs and passes. |
| • | 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 Clear DTC Information
function. |
Diagnostic Aids
Important: When performing the EGR Flow Test, keep 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 following components must be in a steady state: |
| - | Torque converter clutch (TCC) |
| - | Canister purge solenoid |
| • | The PCM will only run the EGR test at vehicle speed above 23 mph. |
| • | If, within the enabling RPM (refer to Conditions for Running the
DTC), the engine speed drops by more than 175 RPM, the PCM will reset the
test. |
| • | If, within the engine RPM (refer to Conditions for Running the
DTC), the engine speed increases by more than 200 RPM, the PCM will reset
the test. |
| • | When the PCM commands the EGR valve open, engine speed will drop.
If the engine speed drops below 700 RPM, the test will not run. |
If the condition is intermittent, refer to
Intermittent Conditions
.
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 the following conditions:
| • | Modification of original installed parts |
- If a condition is found, repair as necessary.
Did you find and correct the condition?
| --
|
Go to Step 5
|
Go to Step 3
|
3
|
- Inspect the EGR system, and related passages and pipes for restrictions,
blockages, and or damage.
- If a condition is found, repair as necessary.
Did you find and correct the condition?
| --
|
Go to Step 5
|
Go to Step 4
|
4
| Replace the EGR
valve. Refer to
Exhaust Gas Recirculation Valve Replacement
.
Is action complete?
| --
|
Go to Step
5
| --
|
5
|
- Review and record the scan tool Fail Records data.
- Clear the DTCs.
- Operate the vehicle within the Conditions for Running the DTC.
- Using the scan tool, select the Specific DTC information for DTC P0401
until the test is complete. This may require 5-15 deceleration samples.
Does the scan tool indicate that DTC P0401 passed?
| --
| System OK
|
Go to Step 2
|
