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 P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0300, P0335, P0336, P0341, and P0342 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 in closed loop. |
| - | The ignition 1 voltage is between 11-16 volts. |
| - | The intake air temperature (IAT) is more than 15°C (59°F). |
| - | The engine coolant temperature (ECT) is more than 60°C (140°F). |
| - | The manifold absolute pressure (MAP) is more than 75 kPa (11 psi). |
| - | The mass airflow (MAF) is between 71-174 mg/tdc. |
| - | The A/C compressor clutch does not change state during deceleration. |
| - | The engine speed is between 1,950-2,600 RPM. |
| - | The EGR is more than 10 percent. |
| • | The DTC runs once an ignition cycle when 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.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
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 Connect End View Reference: Engine Controls 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 | |||||||||
Is DTC P0107 or P0108 also set? | Go to Step 4 | ||||||||||
4 | Inspect the exhaust gas recirculation (EGR) system for the following conditions:
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 | ||||||||
Inspect for the following engine mechanical conditions:
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 | Are there any DTCs that have not been diagnosed? | System OK | |||||||||
