On-Board Diagnostics

The PCM has been programmed to monitor many different circuits of fuel injection system. This monitoring is called "on-board diagnosis". Certain criteria, or "arming conditions", must be met for a trouble code to be entered into PCM memory. The criteria may be a range of: engine RPM, engine temperature, and/or input voltage to PCM. If a problem is sensed with a monitored circuit, and all of criteria or arming conditions are met, a DTC will be stored in PCM.

It is possible that a DTC for a monitored circuit may not be entered into PCM memory even though a malfunction has occurred. This may happen because one of trouble code criteria (arming conditions) has not been met. The PCM compares input signal voltages from each input device with specifications (the established high and low limits of range) that are programmed into it for that device. If input voltage is not within specifications and other trouble code criteria (arming conditions) are met, a trouble code will be stored in PCM memory.