Circuit Description

Exhaust Gas Recirculation (EGR) system controls level of oxides of nitrogen (NOx) emissions by recirculating exhaust gases back into combustion chamber. PCM will apply full manifold vacuum to EGR valve and monitor MAP sensor signal. PCM determines EGR flow to be faulty when monitored MAP sensor pressure change is too small or too large. DTC P0400 will set when:

• Fuel level is greater than 25 percent.
• Intake air temperature is 14-122°F (-10-50°C).
• Engine coolant temperature is 176-230°F (80-110°C).
• Barometric pressure is greater than 11 psi (75 kPa).
• Vehicle speed is greater than 20 MPH.
• Engine speed is 1400-4000 RPM.
• Intake pressure changes during steady driving after 240 seconds from engine start in EGR control mode. Throttle position change is less than .244 degrees in 16 firing events. Intake pressure difference diagnostic will run once per drive cycle for 2 seconds.
• Intake pressure changes during deceleration after 290 seconds from engine start in fuel shut-off mode. Intake pressure difference diagnostic will run once per drive cycle for one second.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of failure and store information in freeze frame buffer.