P0400
DTC P0400 Exhaust Gas Recirculation (EGR) System (1 Of 4):
DTC P0400 Exhaust Gas Recirculation (EGR) System (2 Of 4):
DTC P0400 Exhaust Gas Recirculation (EGR) System (3 Of 4):
DTC P0400 Exhaust Gas Recirculation (EGR) System (4 Of 4):
Exhaust Gas Recirculation (EGR) System:
CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation (EGR) system controls the formation of Oxides of Nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion camber.
CONDITIONS FOR SETTING THE DTC
Intake pressure change during steady state driving conditions:
- Engine coolant temperature between 75°C (167°F) and 110°C (230°F).
- Intake air temperature between -7°C (19°F) and 70°C (158°F).
- Barometric pressure greater than or equal to 75kPa.
- Engine speed between 1500 and 3000 RPM (A/T), 2300 and 4000 RPM (M/T).
- Vehicle speed greater than 32 km/h (20 mph).
- Throttle position change is less than 0.37°/5 msec.
- After 240 seconds from engine start in EGR control mode.
- Intake pressure difference diagnostic will run for 2 seconds, once per drive cycle.
Intake pressure change during deceleration:
- Engine coolant temperature between 75°C (167°F) and 110°C (230°F).
- Intake air temperature between -7°C (19°F) and 70°C (158°F).
- Barometric pressure greater than or equal to 75kPa.
- Engine speed between 1500 and 4000 RPM.
- Engine speed change less than 150 RPM/25 msec.
- Vehicle speed greater than 46 km/h (28 mph).
- After 290 seconds from engine start in fuel shut-off mode.
- Intake pressure difference diagnostic will run for 2 seconds, once per drive cycle.
ACTION TAKEN WHEN THE DTC SETS
- The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.
CONDITIONS FOR CLEARING THE MIL/DTC
- The MIL will turn "OFF" after three consecutive drive cycles without a fault present.
- A DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using a scan tool or by disconnecting the ECM battery feed.
DIAGNOSTIC AIDS
Normal engine operating temperature is specified as 75°C (167°F) or above.
Check the following conditions:
- Vacuum hoses for poor connections, leakage, deterioration, or clogged.
- EGR valve malfunction, stuck closed, stuck open, clogged.
- EGR pressure transducer malfunction.
- EGR solenoid vacuum valve and the EGR bypass valve and their circuitry for malfunctions.
- Poor connection at ECM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness. Inspect the wiring harness for damage.
DTC P0400 is set when the expected change in Manifold Absolute Pressure (MAP) is greater or less than the specified value, when the EGR valve is turned "ON" (opened) and then turned "OFF" (closed). Therefore any condition that can affect the accuracy of the MAP sensor readings should be investigated.
- Retarded ignition timing.
- Restricted exhaust system.
- Faulty vacuum supply hose(s) to the MAP sensor. After all checks have been completed and malfunction continues, replace the ECM with a known good unit and retest.
If DTC P0400 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions since the DTC was last set. This may assist in determining how often the DTC sets.
If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams.
TEST DESCRIPTION
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. Checks for an EGR valve that is staying open.
3. Determine if there are faults in the EGR valve or EGR by-pass valve components. Output controls can be found on the scan tool under Misc. Tests.
4. Determine if fault is present in the EGR pressure transducer or EGR solenoid vacuum valve components. When the engine is cold and at low RPM the EGR valve should not operate. It is necessary for the engine to be at operating temperatures and the ECM to receive a Vehicle Speed Sensor (VSS) signal for EGR operation. Bring engine to operating temperatures and raise rpm. The EGR valve should move accordingly.
5. Driving the vehicle under these conditions will verify that the fault is present. If no DTC sets the fault is intermittent.
9. Determine the cause of the incorrect flow of exhaust gas.
14. After completing the diagnostic procedures and no open or short was found in the EGR by-pass valve control circuit, replace the ECM.
22. After the complete DTC table has been followed and no open or short was found in the EGR solenoid vacuum valve control circuit and the problem still exists, replace the ECM.