Description of On-Board Diagnostics

The charging system is monitored by the engine controller. The engine controller monitors critical input and output circuits within this system, making sure they are operating correctly.

Some circuits are tested continuously; others are checked only under certain circumstances.

Each circuit monitored by the engine controller has a corresponding fault message assigned to it. Refer to "System Fault Messages" below for a list and definition of the fault messages.

- If the on-board diagnostic system senses that one of the circuits is malfunctioning, it stores the corresponding fault message in memory.

- If the malfunction goes away after the fault is stored, the fault message will be erased after 50 key cycles.


Fault messages for charging system diagnostics and their definitions are listed below.

ALTERNATOR FIELD NOT SWITCHING PROPERLY
An open or shorted condition is detected in the alternator field control circuit.

BATTERY TEMP SENSOR VOLTAGE OUT OF LIMIT
Internal controller failure with battery temperature sensor out of range.

CHARGING SYSTEM VOLTAGE TOO HIGH
Battery voltage sense input is above the target charging voltage during engine operation.

CHARGING SYSTEM VOLTAGE TOO LOW
Battery voltage sense input is below target charging voltage during engine operation and no significant change in voltage is detected during active test of alternator output.

Start Counter
The start counter counts the number of times the vehicle has been started since faults were last set, erased, or the battery was disconnected. The counter will count up to 255 starts. When there are no faults stored in memory, the DRBII will display "NO FAULTS DETECTED" and the counter will show "0 FAULTS SINCE ERS".

Using the DRBII, read faults to determine if the fault is the third fault or less. If it is, a start counter of "0" (zero) equals a hard fault. Any other fault is classified as an intermittent fault (except some faults with long mature times, such as "Engine is Cold Too Long").