Diagnostic Instructions
DTC Descriptors
DTC P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient
DTC P0402: Exhaust Gas Recirculation (EGR) Flow Excessive
Circuit/System Description
The engine control module (ECM) performs a insufficient flow test on the exhaust gas recirculation (EGR) system during deceleration and an excessive flow test during engine crank.
The insufficient flow test is when the ECM 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. The ECM will only allow one EGR flow test during an ignition cycle. Following a code clear event, the ECM will perform multiple EGR flow tests.
The excessive flow test is when the ECM monitors the position of the EGR valve during engine crank. The EGR valve should not be open during engine crank.
Conditions for Running the DTC
P0401
| • | DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0351, P0352, P0402, P0404, P0405, P0406, P0502, and P1404 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 A/C compressor clutch does not change state during deceleration. |
| - | The ambient air temperature is more than 3°C (37°F). |
| - | The barometric pressure (BARO) is more than 72 kPa. |
| - | The MAP is between 10-50 kPa. |
| - | The vehicle speed is more than 18 km/h (29 mph) before deceleration. |
| • | The EGR flow test is ran when the following conditions are met during DFCO mode: |
| - | The EGR position is less than 1 percent. |
| - | The engine speed is between 1,550-2,900 RPM. |
| - | The MAP does not vary more than 1 kPa. |
| - | The throttle position does not vary more than 1 percent. |
| • | The EGR flow test is performed once per ignition cycle. |
| • | The DTC runs multiple times on the first ignition cycle after the DTC is cleared from the ECM memory. |
P0402
| • | The engine is cranking. |
| • | The ignition voltage is between 10-16 volts. |
| • | The DTC runs continuously when the above conditions are met . |
Conditions for Setting the DTC
P0401
The MAP changes monitored by the ECM during the EGR flow tests indicate an insufficient amount of EGR flow.
P0402
The ECM detects excessive EGR flow due to the EGR valve pintle being open more than 40 percent during crank.
Action Taken When the DTC Sets
| • | DTC P0401 is a Type C DTC. |
| • | DTC P0402 is a Type B DTC. |
Conditions for Clearing the MIL/DTC
| • | DTC P0401 is a Type C DTC. |
| • | DTC P0402 is a Type B DTC. |
Reference Information
Schematic Reference
Engine Controls Schematics
Description and Operation
Exhaust Gas Recirculation (EGR) System Description
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Engine running, observe the DTC information with a scan tool. Verify that DTC P0106, P0107, P0108, P0401, P0402, P0405, P0406, and P1404 is not set.
- Observe the DTC information with a scan tool. DTCs P0401 or P0402, should not set.
- Ignition ON, observe the scan tool EGR Position Sensor parameter. The reading should be between 0-3 percent.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- Verify none of the following conditions exist:
| • | Incorrect EGR valve for engine application |
| • | A vacuum leak between the EGR valve and the intake manifold |
| • | Signs of external leakage usually indicated by carbon buildup around the mating surfaces of the components or an audible exhaust noise |
| • | Restrictions in the passages or EGR valve caused by carbon deposits or casting flash |
| • | Leaks or restrictions at the MAP sensor |
| | Important: Restrictions can cause excessive back pressure and low engine vacuum.
|
| • | Mechanical failure in the engine such as worn piston rings, camshaft or incorrect timing belt installation--Refer to
Symptoms - Engine Mechanical . |
- Ignition OFF, disconnect the harness connector at the EGR valve.
- Ignition OFF, connect a test lamp between the control circuit terminal 1 or A and 12 volts.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
- If all circuits test normal, test or replace the EGR valve.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
