Circuit Description
The engine control module (ECM) tests the exhaust gas recirculation (EGR) flow once per ignition cycle. When the proper enabling conditions are met, the ECM will close the EGR valve and then open the EGR valve while monitoring the mass air flow (MAF) signal. An expected MAF difference should be detected between the open and closed positions. If the ECM does not see the expected MAF difference, 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 P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0335, P0336, P0340, P0341, P0370, P0374, P0500, P0642, P0643, P2122, P2123, P2127, P2128, P2132, P2133, P2138, P2139, P2140, P2227, P2228, P2229 are not set. |
| • | The engine is running for more than 0.5 seconds. |
| • | The ignition voltage is between 11-18 volts. |
| • | The calculated fuel rate is between 3-20 mm³. This running condition will remain enabled until the calculated fuel rate is less than 2 mm³ or more than 25 mm³ and will not enable again until the calculate fuel rate is between 3-0 mm³. |
| • | The intake air temperature (IAT) is more than 5.25°C (41.5°F). This running condition will remain enabled until the IAT is less than 0°C (32°F) and will not enable again until the IAT is more than 5.25°C (41.5°F). |
| • | The engine coolant temperature (ECT) is between 60-96.75°C (140-206.15°F). This running condition will remain enabled until the ECT is less than 57°C (134.6°F) or more than 99.75°C (211.55°F) and will not enable again until the ECT is between 60-96.75°C (140-206.15°F). |
| • | The barometric pressure (BARO) is more than 74 kPa. This running condition will remain enabled until the BARO is less than 72 kPa and will not enable again until 74 kPa. |
| • | The engine speed is between 640-820 RPM. This running condition will remain enabled until the engine speed is less than 580 RPM or more than 880 RPM and will not enable again until the engine speed is between 640-820 RPM. |
| • | The accelerator pedal position (APP) indicated angle is 0 percent. |
| • | The vehicle speed is less than 0.4 km/h (0.25 mph). |
| • | The power take-off (PTO) is not engaged. |
| • | The ECM is not in limp home mode. |
| • | The above conditions are present for 10 seconds. |
| • | This diagnostic runs once per ignition cycle while the above conditions are met. |
Conditions for Setting the DTC
The MAF difference monitored by the ECM during the EGR flow test indicates an insufficient amount of EGR flow.
Action Taken When the DTC Sets-California
| • | The control module illuminates the MIL on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Action Taken When the DTC Sets-Federal
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
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. |
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Component Views | |||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |||||||||
2 |
Important: Attaching the shop exhaust system to the vehicle may cause false exhaust gas recirculation (EGR) DTCs to set. Did the DTC fail this ignition cycle? | Go to Step 3 | Go to Intermittent Conditions | ||||||||
3 | Is DTC P0101 also set? | Go to Step 8 | Go to Step 4 | ||||||||
4 | Is DTC P0404 or P1404 also set? | Go to Step 5 | |||||||||
5 | Is DTC P0403, P0405, or P0406 also set? | Go to Step 6 | |||||||||
6 | Inspect for engine vacuum leaks. Did you find and correct the condition? | Go to Step 9 | Go to Step 7 | ||||||||
7 | Inspect the exhaust system for leaks, for restrictions, and for a modification of the original equipment manufacture (OEM) parts. Did you find and correct the condition? | Go to Step 9 | Go to Step 8 | ||||||||
8 |
Did you complete the repair? | Go to Step 9 | -- | ||||||||
9 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 10 | ||||||||
10 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |||||||||
