On-Board Diagnostics
The SMEC is equipped with a self-diagnostic system that detects system failures or abnormalities. The self-diagnostic system is divided into 2 categories: faults requiring immediate attention and faults which do not require immediate attention.
Faults requiring immediate attention cause the SMEC to substitute the failed value with a calculated value, to store a trouble code in memory, and to turn on the "CHECK ENGINE" light to alert the driver that service is required. This is the "Limp-In" mode of operation. In this mode, driveability characteristics are greatly affected. The following faulty circuits will cause the system to enter the "Limp-In" mode:
- MAP Sensor If map sensor signal is too low (less than .02 volts), too high (more than 4.7 volts), or not changing (no change from initial pressure reading). The SMEC then uses the TPS signal and engine speed signal to create a substitute MAP signal and a trouble code or codes are stored. Under this condition, the AIS motor is commanded to a preset position by the SMEC.
- TPS If throttle position signal is too low (less than .16 volt) or too high (more than 4.7 volts). The SMEC stores a trouble code, turns on the "CHECK ENGINE" light and uses a modified MAP sensor signal to substitute for failed TPS.
- CTS If coolant temperature signal exceeds 4.96 volts when engine is cold or less than .51 volt with a warm engine, the SMEC stores a trouble code and turns on the "CHECK ENGINE" light. During this malfunction the SMEC will substitute a fixed value of 104°F (40°C) for the failed circuit and the radiator fan will run continuously.
- Battery Voltage If battery voltage signal is less than 4 volts after engine is running for more than one minute, the "CHECK ENGINE" light is turned on and a trouble code is stored. The SMEC will operate the charging system at a fixed rate.
- Battery Voltage Too High If battery voltage exceeds control voltage by more than one volt, the SMEC turns on the "CHECK ENGINE" light and stores a trouble code.