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:

• Intake pressure changes during steady driving with a throttle position change less than.244° in 16 firing events.
• Intake pressure changes during steady driving after 240 seconds from engine start in EGR control mode. 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 1 second.