Diagnostic Aids
When attempting to diagnose an intermittent problem, use scan tool to review malfunction history information. This data can be used to duplicate a problem.
Scan tool can read the number of deceleration tests that have been performed since the DTC(s) were cleared. If can also display the EGR decel average value as well as the fail threshold when DTC was set. The average must be greater than the threshold to set DTC.
Battery voltage is supplied to EGR valve terminal "E" with ignition on. Carbon build-up around pintle valve may restrict exhaust gas flow. Diagnose other DTC(s) first, especially MAP DTC, before diagnosing DTC P0401.