Diagnostic Aids

When attempting to diagnose an intermittent problem, use scan tester to review supplemental diagnostic information. Supplemental data (scan tester MALF HISTORY) can be used to help duplicate an intermittent problem. Using Diagnostic Service Probe (12092782) allows voltage to be read on wires without disconnecting connectors.

PCM will hold IC low if RPM reference is not received from ignition module. PCM resistance with no IC output is about 14,000,000 ohms. If using scan tester, 41A or 41B will display at end of general information table. A 41A indicates IC circuit is open, 41B indicates IC circuit is shorted to ground or voltage. If Code 41 is set with Code 42, use CODES 41 & 42 SIMULTANEOUS chart.

Fig 1: Code 41 Schematic EST Circuit Open Or Shorted

Fig 2: Code 41 Diagnostic Flow Chart EST Circuit Open Or Shorted