Circuit Description
The powertrain control module (PCM) tests the exhaust gas recirculation (EGR) system during deceleration. The PCM does this by momentarily commanding the EGR valve to open while monitoring the signal circuit of the manifold absolute pressure (MAP) sensor. When the EGR valve is opened, the PCM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the PCM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow test counts required to exceed the fail threshold may vary according to the amount of detected EGR flow error.
Normally, the PCM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the PCM will allow up to twelve EGR flow test counts during the first ignition cycle following a code clear event. Between nine and twelve EGR flow test counts should be sufficient for the PCM to determine adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error, DTC P0401 sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0335, P0336, P0404, P0500, P0502, P0503, P0506, P0507, P0562, P0563, P1125, P1404 are not set. |
| • | The ignition 1 signal parameter is between 11-18 volts. |
| • | The throttle position (TP) sensor parameter is less than 1.2 percent. |
| • | The intake air temperature (IAT) sensor parameter is between 0-100°C (32-212°F). |
| • | The engine coolant temperature (ECT) sensor parameter is more than 60°C (140°F). |
| • | The engine speed parameter is between 725-1,700 RPM. |
| • | The manifold absolute pressure (MAP) sensor parameter is between 17-42 kPa. |
| • | The mass air flow (MAF) sensor parameter does not change more than 3 grams per second. |
| • | The vehicle speed sensor parameter is more than 40 km/h (25 mph) during deceleration. |
| • | The barometric pressure (BARO) is more than 74 kPa. |
| • | The vehicle will need to be driven at more than 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 EGR flow test to run. As the EGR flow test is running, you will see the Desired EGR position parameter and the EGR position sensor parameter on the scan tool momentarily change from 0 to a calibrated value above 0. |
Conditions for Setting the DTC
The MAP changes monitored by the PCM during the EGR flow test indicate an insufficient amount of 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/Failure Records data. |
| • | The PCM disables the EGR valve for the ignition cycle. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Inspect for the following conditions:
| • | A vacuum restriction to the MAP sensor--A skewed MAP sensor reading can cause the PCM to read incorrect MAP changes during the EGR flow test. |
| • | An engine that is running poorly due to a mechanical condition--These types of conditions can cause low engine vacuum and thus cause a higher than expected MAP sensor reading. |
| • | Excessive back pressure in the exhaust system may cause this DTC to set. This condition can cause low engine vacuum and thus cause a higher than expected MAP sensor reading. Possible causes of this could be a restriction in the exhaust system or non original equipment manufacture (OEM) exhaust parts. |
| • | Exhaust system leaks can cause an insufficient amount of EGR flow through the EGR valve. This condition can cause less than expected MAP changes due to insufficient exhaust back pressure. Possible causes of this could be a leaking exhaust system, a leaking EGR pipe or non original equipment manufacture (OEM) exhaust parts. |
Test Description
The number below refers to the step number on the diagnostic table.
-
MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
Is DTC P0106, P0107 or P0108 set? | Go to Step 3 | ||
3 | Inspect the exhaust system for leaks, restrictions and for modification of original equipment manufacture (OEM) parts. Did you find and correct the condition? | Go to Step 7 | Go to Step 4 |
4 | Inspect for a vacuum leak between the EGR valve and the intake manifold. Did you find and correct the condition? | Go to Step 7 | Go to Step 5 |
5 |
Did you find and correct the condition? | Go to Step 7 | Go to Step 6 |
6 |
Did you find and correct the condition? | Go to Step 7 | Go to Diagnostic Aids |
7 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 8 |
8 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
