Diagnostic Aids

PCM will not enable the catalyst test if:

Engine speed is plus or minus 100 RPM from desired idle speed.
TP sensor is zero percent.
Short term integrator is -20 percent and 20 percent.

The catalyst test will abort if vehicle falls out of following the conditions:

Engine speed is +/-125 RPM from desired idle speed.
TP sensor is zero percent.
Short term integrator is -20 percent and 20 percent.

The catalyst test may abort due to change in engine load (i.e., A/C, cooling fan on). If this problem occurs, use scan tool to force cooling fans to turn on, then repeat test.

Check for faulty connections or damaged harness. Check PCM harness connector EGR control circuit for backed-out terminal. Observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.