Circuit Description
This diagnostic monitors the operation of the exhaust gas recirculation (EGR) valve. The powertrain control module (PCM) uses expected changes in the manifold absolute pressure (MAP) sensor readings, to evaluate the performance of the EGR system. The PCM tests the EGR system during deceleration. The PCM does this by momentarily commanding the EGR valve to open while monitoring the signal circuit of the 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 suspects that the EGR valve flow is incorrect and this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient
Conditions for Running the DTC
| • | Before the PCM can report DTC P0401 failed, DTCs P0404 and P2413 must run and pass. |
| • | DTC P0030, P0050, P0135, P0155, P0403, P0404, P0443, P0496, P0501, P0506, P0507, P0641, P0651, P2100, P2101, P2108, P2122, P2123, P2127, P2128, P2138, P2176, P2227, P2228, P2229, P2282, P2413, P2414, P2415, P2646, P2647, P2648, P2649, and U0107 are not set. |
| • | The battery voltage is more than 10.5 volts. |
| • | The engine coolant temperature (ECT) is more than 69°C (156°F). |
| • | The engine speed is between 1,100-2,200 RPM. |
| • | The manifold absolute pressure (MAP) sensor is 14 kPa or more. |
| • | The throttle position (TP) sensor indicates a closed throttle. |
| • | The vehicle speed sensor is at least 49 km/h (30 mph) before deceleration. |
| • | The diagnostic test will run during decelerate. |
| • | DTC P0401 runs once per drive cycle after the above conditions have been met. |
Conditions for Setting the DTC
The MAP changes monitored by the PCM during the EGR flow tests indicate an insufficient amount of EGR flow.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (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. |
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 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. |
| • | A restriction in the intake manifold such as carbon deposits and casting flash |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the physical movement of the EGR valve. Normal EGR position voltage at the full open position is 3.10-3.20 volts.
-
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 OEM exhaust parts.
-
Intake system leaks can affect exhaust gas flow into the intake manifold from the EGR valve. This condition can cause a less than expected MAP change causing the DTC P0401 diagnostic to fail.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||
Was the EGR sensor voltage more than the specified value when at 100 percent? | 3.10 V | Go to Step 3 | Go to Step 7 | |||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||
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 8 | Go to Step 5 | |||||||||
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 8 | Go to Step 6 | |||||||||
6 |
Did you find and correct a condition? | -- | Go to Step 8 | Go to Step 7 | ||||||||
7 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | ||||||||
8 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 | ||||||||
9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
