On-Board Diagnostics: Monitors

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Not all monitors will run while operating in CNG mode. In order to complete all monitors, the vehicle will also need to operate in gasoline mode.

Comprehensive Component Monitor

Monitors PCM systems for opens, shorts grounds and out-of-range sensors. Also monitors rationality of sensors. Rationality is whether the sensors value is consistent with the operating conditions of the other sensors.

Misfire Monitor

Monitors engine misfire using crankshaft sensor to determine location and severity of misfire. A catalyst damaging misfire will flash the MIL, and a non-catalyst damaging misfire is a normal type "B" code.

Fuel Trim Monitor

Monitors short and long term fuel trim for being at maximum lean or rich limit.

Oxygen Sensor Monitor

Monitors all oxygen sensors for maximum voltage level, minimum voltage level and lean rich/rich lean switching rate.

Oxygen Sensor Heater Monitor

Monitors oxygen sensor heater by watching sensor's time-to-activity after a cold start.

Catalyst Monitor

Monitors catalyst efficiency by comparing activity rate of pre-catalyst oxygen sensor and post-catalyst oxygen sensor.

EVAP Monitor

Monitors EVAP system for large leaks, small leaks and purge flow.