Diagnostic Aids

WARNING: This page is about a different car, the 2000 Isuzu Rodeo and 2000 Isuzu Amigo. However, it is still accessible from the selected car via links, so may be relevant.

Check for poor connection at PCM. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal connection. Observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location.

Ensure engine has reached operating temperature. Place gear selector in Park. Using scan tool, monitor HO2S-1 and HO2S-2 values while using scan tool IAC RPM function to maintain MAF at 10 grams per second. Compare activity between HO2S-1 and HO2S-2 for 30 seconds. If activity between both HO2S is about equal, a problem exists. Repeat DTC P0420. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.