Theory Of Operation
The Clutch Pedal Position Sensor has been added to detect the actual position of the pedal during the full range of travel. This is necessary for better control of features like Electric Stop/Start (ESS) and Active Cruise Control (ACC). The Powertrain Control Module (PCM) performs the normal circuit low/high diagnostics on the sensor. The PCM also performs continuous diagnostics for a stuck sensor during driving. Vehicles equipped with ESS also use an interlock switch for correlation with the sensor to aid in rapid detection of interlock switch or sensor faults.
Clutch Pedal Position Sensor Operation and Diagnostics: At the plant, a Clutch Position Learn Procedure is performed. The Clutch Position Sensor minimum and maximum voltage readings are programmed into the PCM permanent memory. The Clutch Position Sensor voltage is monitored when the enable conditions are met for a stuck Clutch Position Sensor as follows:
- When the vehicle is not moving, or moving very slowly (below 2 mph), the PCM assumes that the Clutch Pedal is depressed, or must be depressed at some point to put the Transmission in gear, and the maximum voltage reading is recorded.
- When the PCM detects a vehicle launch condition, it is assumed that the Clutch pedal is released and the minimum voltage reading is recorded.
A vehicle launch is determined to be true based on the following conditions:
- Throttle input is requested
- Increased engine load
- Vehicle is accelerating
- When the vehicle speed reaches a calibrated value, the launch event is considered complete
If the difference between the maximum voltage recorded and the minimum voltage recorded (delta) is not greater than a calibrated threshold, a performance fault is set. The graphic below illustrates the performance diagnostic. The threshold values are approximate. The calibrations can vary between vehicles.
Vehicles equipped with ESS will also have a Clutch Interlock Switch. The Clutch Interlock Switch is different than the traditional Clutch Pedal Switches in that it only detects the interlock (pedal depressed) position. The switch input is compared to the Clutch Position Sensor signal for the correlation diagnostic. The next two graphics illustrate the correlation diagnostic pass/fail. The threshold values are approximate. The calibrations can vary between vehicles. If a correlation fault sets it will affect the ESS system in one of the following ways:
- If the fault occurs prior to an Auto/Stop, ESS will be disabled and no Auto/Stop will occur.
- If the fault occurs during an Auto/Stop with the Transmission in neutral, the vehicle will Auto/Start and ESS will then be disabled.
- If the fault occurs during an Auto/Stop with the Transmission in gear, Vehicle will not start until the shifter is moved into neutral and then ESS will be disabled.