Circuit Description
The PCM controls the movement of the 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
| • | TP sensor, MAP sensor, VSS, ECT sensor, Idle speed, EGR Pintle
Position, EVAP purge solenoid, IAT sensor, MAF sensor, Misfire, CKP sensor,
or transaxle DTCs are not set. |
| • | The system voltage is between 11-16 volts. |
| • | The engine speed is between 1000-1500 RPM. |
| • | The ECT is between 80°C-110°C (176°F-230°F). |
| • | The vehicle speed is more than 12 mph. |
| • | The BARO is more than 70 kPa (10.15 psi). |
| • | Throttle is steady below 2 percent. |
| • | The transaxle is steady. |
| • | The Torque Converter Clutch (TCC) is steady. |
| • | The canister purge duty cycle is steady. |
| • | The A/C clutch is steady. |
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) 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: |
| - | The torque converter clutch (TCC) |
| - | The canister purge solenoid |
| • | The PCM will only run the EGR test at vehicle speeds above 12 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 800 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 the 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
|
