On-Board Diagnostic System

If information from certain critical engine sensors fail internal Engine Controller self checks, the controller turns on the Check Engine Lamp and substitutes a modified signal in place of the one that failed until repairs can be made.

The following is a description of each "limp-in" mode:
1. MAP (MANIFOLD ABSOLUTE PRESSURE) SENSOR - If this signal is either too low, too high or not changing, one of a series of MAP failure messages is set into the Controller's memory and the Check Engine Lamp is switched on. At this time the Throttle Position and Engine Speed Signals are used by the Engine Controller to generate a "modified" MAP signal in place of the one that failed.
2. THROTTLE POSITION SENSOR - If this signal is either too high or too low, a TPS message is stored in memory. The Check Engine lamp is turned on, and a "modified" MAP signal is generated to replace the failed Throttle Position Sensor.
3. COOLANT TEMPERATURE SENSOR - If this signal is out of range, a coolant error message is stored and the Check Engine Lamp is turned on. At this time the Engine Controller will operate at a default temperature of 104 degrees F.
4. BATTERY VOLTAGE SENSE - If this signal drops below 4 volts after the engine has been running for one minute, a "Battery Input Sense" message is stored in memory and the Check Engine Lamp is turned on. At this time the engine controller will operate the charging system at a fixed rate.
5. BATTERY VOLTAGE TOO HIGH - If the charging voltage rises 1 volt above desired control voltage this message is set in memory and the Check Engine Lamp is turned on.
6. INJ PEAK CURRENT - Caused by a high resistance in control circuit any time engine is running.
7. INJ CONTROL CKT - If the engine controller does not sense injectors switching on and off when a control is switched. Checked during any engine running.

If these sensor signals return to within specifications while the engine is running, the system will return to normal operation, but the "check engine" lamp will stay "ON" until the engine is truned off and then restarted. The fault code will remain in memory for evaluation by the technician but will be cleared after 50 engine starts if the fault does not happen again.