THEORY OF OPERATION
The Powertrain Control Module (PCM) predicts what the engine coolant temperature should be, based on the engine coolant temperature at start-up, ambient temperature and how the vehicle is subsequently driven. The predicted engine coolant temperature is compared to the Engine Coolant Temperature (ECT) Sensor reading. The error between the two is calculated and integrated with respect to time. When the Thermostat diagnostic runs, the integrated error is compared to a calibrated threshold and pass/fail is determined. Separate pass and fail thresholds are used in order to improve accuracy of the diagnostic.
The fuel feedback system will maintain a stoichiometric air/fuel mixture, 14.7:1, by modifying the injector pulse width according to the oxygen content of the exhaust gas. The Powertrain Control Module (PCM) makes short term and long term fuel corrections to maintain stoiciometric air/fuel ratio for best Catalytic Converter efficiency. If one or more cylinders do not operate at stoichiometric then the high frequency content of the O2 Sensor will increase. Short term fuel correction is based on Upstream O2 Sensor output and is designed for quick engine response. The long term fuel correction compensated for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich and lean conditions over a longer period of time.
The fuel feedback system will maintain a stoichiometric air/fuel mixture, 14.7:1, by modifying the injector pulsewidth according to the oxygen content of the exhaust gas. The Powertrain Control Module (PCM) makes short term and long term fuel corrections to maintain stoiciometric air/fuel ratio for best Catalytic Converter efficiency. If one or more cylinders do not operate at stoichiometric then the high frequency content of the O2 Sensor will increase. Short term fuel correction is based on Upstream O2 Sensor output and is designed for quick engine response. The long term fuel correction compensated for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich and lean conditions over a longer period of time.
The Oxygen sensors (O2 Sensor) are used for fuel control and catalyst monitoring. Each O2 Sensor compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 Sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 Sensor heats the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 Sensor heats up and begins to generate a voltage within a range of 0-1, 275 mV. Once sufficient O2 Sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 Sensor voltage to determine the air-to-fuel ratio. An O2 Sensor voltage that increases toward 1, 000 mV indicates a rich fuel mixture. An O2 Sensor voltage that decreases toward 0 mV indicates a lean fuel mixture.
The Oxygen sensors (O2 Sensor) are used for fuel control and catalyst monitoring. Each O2 Sensor compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 Sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 Sensor heats the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 Sensor heats up and begins to generate a voltage within a range of 0-1, 275 mV. Once sufficient O2 Sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 Sensor voltage to determine the air-to-fuel ratio. An O2 Sensor voltage that increases toward 1, 000 mV indicates a rich fuel mixture. An O2 Sensor voltage that decreases toward 0 mV indicates a lean fuel mixture.
The downstream O2 Sensor is located in the exhaust path behind the Catalytic Converter and is monitored for proper response to assure optimum Catalytic Converter efficiency. The downstream O2 Sensor response monitor is intended to diagnose a downstream O2 Sensor that is not moving or stuck in a voltage window and to insure accurate information for catalyst monitor diagnosis.
The downstream O2 Sensor is located in the exhaust path behind the Catalytic Converter, is monitored for proper response to assure optimum Catalytic Converter efficiency. The downstream O2 Sensor response monitor is intended to diagnose a downstream O2 Sensor that is not moving or stuck in a voltage window and to insure accurate information for catalyst monitor diagnosis.
The Electric Vacuum Pump (EVP) system is installed to provide supplemental vacuum to the brake booster, when the engine vacuum supply is low. The pump is connected to the engine and the brake booster through a series of hoses and one-way flow check valves. A pressure sensor, mounted in the brake booster, provides information to the ABS/ESP Module. This information is then sent to the Powertrain Control Module (PCM) over the CAN C BUS. The PCM modulates the EVP operation to maintain the brake booster vacuum within a given range. This system ensures that the customer experiences a consistent brake pedal feel under all driving conditions.
The Electric Vacuum Pump (EVP) system is installed to provide supplemental vacuum to the brake booster, when the engine vacuum supply is low. The pump is connected to the engine and the brake booster through a series of hoses and one-way flow check valves. A pressure sensor, mounted in the brake booster, provides information to the ABS/ESP Module. This information is then sent to the Powertrain Control Module (PCM) over the CAN C BUS. The PCM modulates the EVP operation to maintain the brake booster vacuum within a given range. This system ensures that the customer experiences a consistent brake pedal feel under all driving conditions.
The Powertrain Control Module (PCM) compares actual shutdown time to a calculated shutdown time value. The calculated shut down time value is based on the amount of shutdown time necessary for the ECT to drop a specific amount after a completely warmed up engine is shut down. If the difference between actual shutdown time and the calculated shut down time is greater than a maximum value, a one trip failure will set. The shutdown time is measured again after one hour of ignition off time following the next engine warm up cycle. The PCM compares the shutdown time to a calculated value. If the difference is greater than a maximum value, the MIL is illuminated and a DTC will set.
The ambient temperature sensor signal is a direct input to the Totally Integrated Power Module (TIPM). The TIPM sends the PCM the ambient temperature signal over the CAN C bus.
The Powertrain Control Module (PCM) receives the vehicle speed signal over the CAN C bus from the Anti-lock Brake Module.
The A/C Pressure Transducer signal is a direct input to the Totally Integrated Power Module (TIPM). The TIPM sends the PCM the A/C pressure signal over the CAN C bus.
The PCM receives the vehicle speed signal over the CAN C bus from the Anti-lock Brake Module.
The TIPM transmits the fuel level message to the Powertrain Control Module (PCM) over the CAN C bus.
The Powertrain Control Module (PCM) receives wheel speed and wheel distance CAN bus messages from the Anti-lock Brake (ABS) module.
The Powertrain Control Module (PCM) receives wheel speed and wheel distance CAN bus messages from the Anti-lock Brake (ABS) module.