System Diagnostics: Notes

WARNING: This page is about a different car, the 1995 Jeep Wrangler, 1995 Jeep Grand Cherokee, and 1995 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Malfunction Indicator Light (MIL) may also be referred to as CHECK ENGINE light.

The self-diagnostic capabilities of this system, if properly utilized, can simplify testing. The Powertrain Control Module (PCM) monitors and controls engine, fuel and ignition system circuits.

If a problem is sensed with a monitored circuit, PCM memory stores a Diagnostic Trouble Code (DTC), the MIL glows and PCM enters limp-in mode. In limp-in mode, PCM compensates for component failure by substituting information from other sources. This allows vehicle operation until repairs can be made.

Test circuits and repair or replace components as required. If problem is repaired or ceases to exist, PCM cancels DTC after 51 ignition on/off cycles.

A specific DTC results from a particular system failure. A DTC does not condemn a specific component; component is not necessarily the reason for failure. DTCs only call out a probable malfunction area.