Circuit Description
The engine control module (ECM) tests the exhaust gas recirculation (EGR) system during deceleration. The ECM 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 ECM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the ECM 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 ECM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the ECM will allow up to 27 EGR flow test counts during the first ignition cycle following a code clear event. Between 8-14 EGR flow test counts should be sufficient for the ECM to determine adequate EGR flow and pass the EGR flow test. If the ECM detects an EGR flow error, DTC P0401 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient
Conditions for Running the DTC
| • | DTCs P0016, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0122, P0123, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0220, P0222, P0223, P0300, P0301-P0308, P0315, P0335, P0336, P0340, P0341, P0403, P0404, P0502, P0503, P0601, P0602, P0603, P0604, P0606, P060D, P062F, P0641, P0651, P1404, P2135 are not set. |
| • | The Ignition 1 signal parameter is between 11-18 volts. |
| • | The Current Gear parameter does not change. |
| • | The Intake Air Temperature (IAT) sensor parameter is less than 100°C (212°F). |
| • | The Engine Coolant Temperature (ECT) sensor parameter is between 5-150°C (41-230°F). |
| • | The Engine Speed parameter is between 1,000-1,800 RPM. |
| • | The Manifold Absolute Pressure (MAP) sensor parameter is between 11-50 kPa. |
| • | The Mass Air Flow (MAF) sensor parameter does not change more than 2 grams per second. |
| • | The Barometric Pressure (BARO) parameter is more than 74 kPa. |
| • | The Throttle Position (TP) sensor parameter is less than 1.19 percent. |
| • | The Vehicle Speed sensor parameter is more than 37 km/h (23 mph) during deceleration. |
| • | The vehicle will need to be driven 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 ECM 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. Additionally, the EGR Flow Test Count parameter on the scan tool will increment when each EGR flow test is completed. |
| • | DTC P0401 runs once per trip typically, or 7 tests will be run per trip until 42 tests have been completed. |
Conditions for Setting the DTC
The MAP changes monitored by the ECM during the EGR flow tests indicate an insufficient amount of EGR flow for more than 2.8 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
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 ECM to read incorrect MAP changes during the EGR flow test. |
| • | An engine that is running poorly due to a mechanical condition such as worn piston rings, worn camshaft, etc.--These types of conditions can cause low engine vacuum and thus can cause a less than expected MAP changes during the flow test. |
| • | Excessive back pressure in the exhaust system may cause this DTC to set. This condition can cause low engine vacuum and thus can cause a less than expected MAP changes during the EGR flow test. 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 a 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. |
| • | A restriction in the intake manifold such as carbon deposits and casting flash |
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 Control Module Connector End Views or Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
Is DTC P0107 or P0108 also 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 exhaust gas recirculation (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 | |
