Description of On-Board Diagnostics
FOR CERTAIN COOLING SYSTEM COMPONENTSThe Powertrain Control Module (PCM) has been programmed to monitor certain cooling system components:
NOTE: If the engine has remained cool for too long a period, such as with a stuck open thermostat, a Diagnostic Trouble Code (DTC) number 17 can be observed at the malfunction indicator lamp. This lamp is displayed on the instrument panel as the CHECK ENGINE lamp.
If the problem is sensed in a monitored circuit often enough to indicate an actual problem, a DTC is stored. The DTC will be stored in the PCM memory for eventual display to the service technician. If the problem is repaired or ceases to exist, the PCM cancels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be entered into PCM memory. The criteria may be a specific range of engine rpm, engine temperature and/or input voltage to the PCM.
A DTC indicates that the PCM has recognized an abnormal signal in a circuit or the system. A DTC may indicate the result of a failure, but never identify the failed component directly.
It is possible that a DTC for a monitored circuit may not be entered into memory even though a malfunction has occurred. Refer to On-Board Diagnostics (OBD) in Powertrain Management for additional information.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be displayed by cycling the ignition key On-Off-On-Off-On within three seconds and observing the malfunction indicator lamp. This lamp is displayed on the instrument panel as the CHECK ENGINE lamp.
They can also be displayed through the use of the Diagnostic Readout Box (DRB) scan tool. The DRB connects to the data link connector, left of the steering column above the brake pedal. For operation of the DRB, refer to Powertrain Management for the appropriate Powertrain Diagnostic Procedures.
EXAMPLES:
- If the lamp flashes 1 time, pauses and flashes 2 more times, a flashing Diagnostic Trouble Code (DTC) number 12 is indicated. If this code is observed, it is indicating that the battery has been disconnected within the last 50 key-on cycles. It could also indicate that battery voltage has been disconnected to the PCM. In either case, other DTC's may have been erased.
- If the lamp flashes 1 time, pauses and flashes 7 more times, a flashing Diagnostic Trouble Code (DTC) number 17 is indicated.
After any stored DTC information has been observed, the display will end with a flashing DTC number 55. This will indicate the end of all stored information.
ERASING TROUBLE CODES
After the problem has been repaired, use the DRB scan tool to erase a DTC. Refer to Powertrain Management for the appropriate Powertrain Diagnostic Procedures for operation of the DRB scan tool.