P0400

Wiring Diagram:

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

Vacuum to the Exhaust Gas Recirculation (EGR) valve is controlled by the EGR vacuum control signal solenoid valve. The vacuum signal to the EGR valve is regulated by varying the duty cycle (on-time) of the solenoid valve. The duty cycle is calculated by the PCM based on data from the ECT sensor, the MAF sensor and RPM. The PCM uses engine coolant temperature (ECT) and intake air temperature (IAT) to determine when to enable the EGR system. It the ambient temperature is cool when the vehicle is started, IAT is below 15°C (59°F), the PCM will wait longer before enabling the EGR, the EGR will not be enabled until ECT reaches 82°C (180°F). In warmer ambient temperatures, the PCM will allow the EGR system to operate earlier in the warm up cycle [If IAT is above 15°C.(9°F) at start up, EGR will be enabled when ECT reaches 80°C (140°F). EGR operation is prevented under the following additional conditions:

^ Transmission is in Park/Neutral

^ Throttle Angle is less than a predetermined value

^ At wide open throttle (WOT)

The PCM tests the EGR system operation during specific driving conditions.

CONDITIONS FOR SETTING THE DTC Enabling Conditions:

^ DTCs P0107, P0108, P0112, P0113, P0117, P0118, P01221 P0123, P0601, P0719, P0724 not set.

^ Coolant above 27°C (81°F)

^ Vehicle speed above 14 mph

^ Baro above 95 kPa

^ RPM between 500 and 900

^ IAC steady

^ MAP less than 24 kPa

^ NO clutch, TCC, Brake switch, no transitions

Test Conditions:

Decel Mode Test

^ TP Sensor below 1%

^ Not in DFCO

^ EGR duty cycle = 0%

^ The expected change in MAP is less than a predetermined amount when the PCM commands EGR ON during the test.

^ MAP within the range shown in the table (depends on altitude) and steady.

ACTION TAKEN WHEN THE DTC SETS

^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.

^ The PCM will record operating conditions at the time the diagnostic tails. This information will be stored in the Freeze Frame and/or Failure Records.

^ The injector will be disabled for the entire ignition cycle.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

^ A last test tailed (Current DTC) will clear when the diagnostic runs and does not fail.

^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

^ PCM battery voltage is interrupted.

^ Using a Scan tool.

DIAGNOSTIC AIDS

^ Suction from shop exhaust hoses can alter back pressure and may affect the operation of the EGR valve during in-stall testing. This DTC can be set by a leaking exhaust system because an exhaust leak alters back pressure. Thoroughly check the exhaust system for leaks. Refer to Exhaust System.

^ Vacuum lines should be thoroughly checked for proper routing. The vacuum source goes to the orifice side of the solenoid valve. Refer to the Vehicle Emissions Control Information label.

^ Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.

A leaking EGR valve pipe assembly will cause an exhaust leak and can reduce EGR flow volume.

For intermittents, refer to Symptoms. Testing and Inspection

TEST DESCRIPTION

Number(s) below refer to step numbers on the diagnostic table.

10. Intake Passage: Turn the engine OFF. Remove the EGR valve from the manifold. Plug the exhaust side hole with a suitable stopper. With the intake side hole open, attempt to start the engine. If the engine runs at a very high idle (up to 3000 RPM is possible), or starts and stalls, the EGR passages are not restricted. If the engine starts and idles normally, the EGR intake side passage in the intake manifold is restricted. Refer to EGR System for more information.

Exhaust Passage: With the EGR valve still removed, plug the intake side hole with a suitable stopper. With the exhaust side hole open and the engine running, check for the presence of exhaust gas. If no exhaust gas is present, the EGR exhaust side passage in the intake manifold is restricted. Refer to EGR System for more information.