Circuit Description
The engine control module (ECM) performs a flow test on the exhaust gas recirculation (EGR) system during deceleration. The ECM does this by momentarily commanding the EGR valve to open while monitoring the signal of the manifold absolute pressure (MAP) sensor and the EGR position sensor. If the MAP signal is incorrect for the EGR pintle position, 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 tests required to exceed the fail threshold may vary according to the amount of detected EGR flow error. If the ECM detects an EGR flow error, DTC P0400 sets.
Normally, the ECM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the ECM will allow multiple EGR flow tests following a code clear event.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0400 Exhaust Gas Recirculation (EGR) Flow Incorrect
Conditions for Running the DTC
| • | DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0151, P0152, P0153, P0171, P0172, P0174, P0175, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0341, P0342, P0501, P0562, P0563, P1171, P1172, P1173, P1174, P1504, P1562, and P1563 are not set. |
| • | The EGR flow test is ran in decel fuel cut-off (DFCO) mode with the following conditions present before deceleration occurs: |
| - | The engine is operating. |
| - | The ignition 1 voltage is between 11-16 volts. |
| - | The ambient air temperature is more than 6°C (43°F). |
| - | The engine coolant temperature is more than 55°C (131°F). |
| - | The A/C compressor clutch does not change state during deceleration. |
| - | The engine speed is between 1,400-3,200 RPM before deceleration. |
| - | The EGR has been active for 20 seconds before deceleration. |
| - | The barometric pressure (BARO) is more than 74.5 kPa. |
| • | DTC P0400 runs once an ignition cycle once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects the incorrect amount of intake absolute pressure when compared to the EGR valve position during the EGR flow test for 5 seconds.
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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.
-
An engine mechanical condition may cause the engine to operate poorly, which could cause a low vacuum condition.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | |||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |||||||||
2 |
Did the DTC fail this ignition? | Go to Step 3 | Go to Intermittent Conditions | ||||||||
Is DTC P0106, P0107, or P0108 also set? | Go to Step 4 | ||||||||||
4 | Inspect the exhaust gas recirculation (EGR) system for the following conditions:
Refer to Exhaust Gas Recirculation Valve Replacement and Exhaust Gas Recirculation Valve Pipe Replacement . Did you find and correct the condition? | Go to Step 9 | Go to Step 5 | ||||||||
5 | Inspect for leaks or restrictions at the manifold absolute pressure (MAP) sensor. Did you find and correct the condition? | Go to Step 9 | Go to Step 6 | ||||||||
6 | Inspect the exhaust system for the following conditions:
Did you find and correct the condition? | Go to Step 9 | Go to Step 7 | ||||||||
Did you find and correct the condition? | Go to Step 9 | Go to Step 8 | |||||||||
8 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Did you complete the replacement? | 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 | |||||||||
