Modes of Operation

If information from seven critical sensors fails certain on-board diagnostic tests, the single module engine controller (SMEC) goes into a "limp-in" mode, truns on the check engine lamp and substitutes a modified signal in place of the failed one, in order to keep vehicle driveable.

The following is a description of each "limp-in" mode:

1. M.A.P. (Manifold Absolute Pressure) Sensor. If this signal is either too low, (less than .02 volts) too high, (greater than 4.7 volts) or not changing fault codes 13 and/or 14 are recorded in memory and the "check engine" lamp is turned "ON". At this time the throttle position and engine speed signals are used by the SMEC to generate a modified M.A.P. sensor signal in place of the failed one. While in this "limp-in" mode the automatic idle speed motor is driven to a preset position.
2. Throttle Position Sensor. If this signal is either too low (less than .16 volts) or too high (greater than 4.7 volts) fault code 24 is recorded in memory and the "check engine" lamp is turned "ON". At this time the M.A.P. sensor signal is used by the SMEC to generate a modified throttle signal in place of the failed one.
3. Coolant Temperature Sensor. If this signal is above 4.96 volts when the engine is cold or below .51 volts with a warm engine fault code 22 is recorded in memory and the "check engine" lamp is turned "ON". At this time the SMEC will set in a fixed value off 104 degrees F. The radiator fan will run continuously in this mode.
4. Battery Voltage Sense. If this signal drops below 4 volts after the engine has been running for one minute fault code 16 is recorded in memory and the "check engine" lamp is turned "ON". At this time the SMEC will operated the charging system at a fixed rate.
5. Battery Voltage Too High. If the SMEC senses the battery sense voltage is more than 1 volt above the desired control voltage, fault code 46 is recorded in memory and the "check engine" lamp is turned "ON".

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 stat "ON" until the engine is restarted. The fault code will remain in memory for evaluation by the SMEC but will be cleared after 50 to 100 engine starts if the fault does not happen again.