Circuit Description

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.

PCM tests EGR system during deceleration by momentarily commanding EGR valve to open while monitoring Manifold Absolute Pressure (MAP) sensor signal. When EGR valve is opened, PCM monitors change in MAP sensor input signal. PCM compares MAP change to a RPM vs. BARO table. When PCM interprets change in MAP sensor to be out of limits, PCM will set DTC P0401. Number test samples required to accomplish this may vary according to severity of detected flow error. Normally, PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, PCM allows 12 test samples during first ignition cycle following a scan tool CLEAR INFO command or a battery disconnect. Between 9 and 12 samples should be sufficient for PCM to determine adequate EGR flow and to pass EGR test.

When DTC sets, PCM illuminates MIL on second trip after fault was detected. PCM will store conditions present when DTC was set as freeze frame data in the FAILURE RECORDS data.