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Part 6

14 COMPREHENSIVE COMPONENTS MONITORING Contd.

14.14 Vehicle speed sensor (VSS)

14.14.1 Vehicle Speed Signal Monitoring via ESP/ABS

Applicable only for test groups:






14.14.1.1 General Description
The vehicle speed signal faults detected by the ESP/ABS control module are transmitted to the ECM via the FlexRay/CAN bus by means of an OBD error nibble (= half-byte = 4 bits) which contains the fault information of each wheel speed sensor. Obtaining the fault information, the ECM forwards it to its fault memory. A fault code is only registered in the ECM if none of the wheel speed sensors provides the ESP/ABS control module with a valid signal, and thus the MIL is commanded on if none of the wheel speed sensors is fault-free.






14.14.1.2 Vehicle Speed Signal faulty - P0501/P0502

Monitoring Strategy
The EPS/ASB fault memory is read out.

Typical Enable Conditions
These diagnostics in the brake control module are run continuously; hence no enable conditions are defined.

Malfunction Criteria
In the ESP/ABS control module, the individual fault states of the wheel speed sensors are mapped to an error nibble, and in the ECM they are classified either as electrical faults or rationality faults and assigned to a P-Code, respectively. The MIL is commanded on if none of the individual signals from the wheel speed sensors is assessed as fault-free.






14.15 Electronic Throttle Unit

14.15.1 General Description
The Electronic Throttle Unit controls the engine charge by adjusting the throttle via a direct-current servo motor and a gear mechanism.
The engine control module calculates the required opening angle of the throttle from the accelerator pedal position and adjusts the throttle drive correspondingly. The throttle position is detected by two sensors (potentiometers). The voltages of the two sensors (potentiometers) vary depending on the throttle position and are transmitted to the engine control module separately. The fault detection for throttle position sensor 1 and throttle position sensor 2 are carried out similarly. The throttle plate, the throttle drive, and the throttle position sensors are integrated into one unit, called the throttle unit.






14.15.2 Throttle Position Sensor, Signal Range Fault - Signal Voltage too high / too low, P0123, P0223 / P0122, P0222
Signal Voltage too high: Sensor 1: P0123; Sensor 2: P0223
Signal Voltage too low: Sensor 1: P0122; Sensor 2: P0222

Monitoring Strategy
The two sensor voltages 1 and 2 are monitored and evaluated separately.

Typical Enable Conditions
- None

Malfunction Criteria
The sensor voltage 1 is compared to a positive upper / lower threshold value 1, and the sensor voltage 2 is compared to a positive upper / lower threshold value 2. If one of the two sensor voltages exceeds its upper threshold value, this sensor is detected as faulty (voltage too high). If one of the two sensor voltage is lower than its lower threshold value, this sensor is detected as faulty (voltage too low). The corresponding fault is registered in the fault memory. If both sensor voltages exceed their upper threshold values or are lower than their lower thresholds, both sensors are detected as faulty and the corresponding faults are registered in the fault memory.






14.15.3 Throttle Position Sensor, Signal irrational, P0121, P0221
Sensor 1: P0121; Sensor 2: P0221

Monitoring Strategy
The signal voltages of the two throttle position sensors are compared to each other and to a modeled reference voltage.

Typical Enable Conditions
- Engine speed > defined threshold value

Malfunction Criteria
The relative percent difference between the two signal voltages of throttle position sensor 1 and throttle position sensor 2 is calculated.
Additionally, the relative percent difference between the signal voltage of throttle position sensor 1 and a modeled reference voltage, and the relative percent difference between the signal voltage of throttle position sensor 2 and a modeled reference voltage are calculated.
An irrational signal is detected and the corresponding fault is registered in the fault memory if the following malfunction criteria are present:

The absolute value of the relative percent difference between the two signal voltages 1 and 2 is greater than a defined positive threshold value AND the two absolute values of the relative percent difference between the signal voltages and the modeled reference voltage are not the same.

OR:

The absolute value of the relative percent difference between the signal voltage of the throttle position sensor 1 and the modeled reference voltage is greater than a defined positive threshold value.

OR:

The absolute value of the relative percent difference between the signal voltage of the throttle position sensor 2 and the modeled reference voltage is greater than a defined positive threshold value.






14.15.4 Throttle Unit, Result for the Return Spring Test irrational, P0638

Monitoring Strategy
The amount of time for the throttle blade to close to a defined reference position is monitored.

Typical Enable Conditions
- Engine speed = 0
- Vehicle speed = 0
- Engine coolant temperature > defined threshold value
- Ambient air temperature > defined threshold value
- Ignition ON

OR

- Engine-off time > defined threshold value

Malfunction Criteria
The correct function of the return spring is tested by opening the throttle plate to a defined position and measuring the amount of time it takes to close to a defined reference position due to the spring force of its return spring. If this "closing time" exceeds a defined threshold value, an irrational result of the return spring functional test is detected and the corresponding fault is registered in the fault memory.






14.15.5 Throttle Unit, Signal Range Fault - Initialization faulty, P0638

Monitoring Strategy
The signal voltages of the two throttle position sensors are evaluated when the throttle is at its lower stop.

Typical Enable Conditions
- Engine speed = 0
- Vehicle speed = 0
- Engine coolant temperature within defined range
- Ambient air temperature within defined range
- Ignition ON

OR

- Engine-off time > defined threshold value

Malfunction Criteria
The throttle is driven to its lower mechanical stop (throttle closed). Then the signal voltages of the throttle position sensors are evaluated. If the signal voltage of the throttle position sensor 1 OR the signal voltage of the throttle position sensor 2 OR the sum of both sensor voltages is out of the respectively defined range, a faulty initialization of the throttle is detected and the corresponding fault is registered in the fault memory.






14.15.6 Throttle Unit, Signal Range Fault - Pulse Duty Factor too high, P2101

Monitoring Strategy
The throttle motor is controlled by the ECM by using a rectangular pulse-width modulated signal (PWM signal). The pulse duty factor (Ratio of impulse duration to period duration) of this signal is evaluated.

Typical Enable Conditions
- None

Malfunction Criteria
If the pulse duty factor of the pulse-width modulated signal exceeds a defined threshold value AND no fault of the throttle drive output stage is present, the corresponding fault is detected and registered in the fault memory.






14.15.7 Throttle Unit, Signal irrational, P2101

Monitoring Strategy
The setpoint value and the actual value of the throttle position are compared to each other.

Typical Enable Conditions
- None

Malfunction Criteria
If the difference between the set point value and the actual value of the throttle position exceeds a defined threshold value, an irrational signal is detected and the corresponding fault is registered in the fault memory.

14.15.8 Throttle Actuator Control System, System fault, P2106

Monitoring Strategy
Certain functions of the throttle unit are monitored through self-testing by the throttle unit output stage in the ECM.

Typical Enable Conditions
None

Malfunction Criteria
The throttle unit output stage in the ECM can detect the following faults of the throttle unit by self-monitoring, and registers the corresponding faults in the fault memory:
- Short circuit to ground
- Short circuit to plus
- Open circuit
- Temperature too high
- Electric current consumption too high

14.16 Accelerator Pedal Position Sensor Monitoring (APPS)

14.16.1 General Description
In the electronic throttle control system, two Hall-effect sensors (sensor 1 and sensor 2) are used to measure the position of the accelerator pedal. The relative position of a permanent magnet to the Hall-effect sensors changes with the pedal position. The change in the magnetic field around the sensors caused by this results in a change of the occurring Hall voltages. The Hall voltage values of the two sensors are amplified and sent to the ECM as separate signals. The fault monitoring of sensor 1 and 2 is identical.

14.16.2 Signal Range Fault, Signal Voltage too high / low, P2123, P2128 / P2122,P2127
Too high: Sensor 1: P2123; Sensor 2: P2128
Too low: Sensor 1: P2122; Sensor 2: P2127

Monitoring Strategy
The signal voltage is continuously monitored and evaluated.

Typical Enable Conditions
- None

Malfunction Criteria
Signal Voltage too high:
The signal voltage is compared to a positive threshold value. If the voltage exceeds this positive threshold value, a signal is detected which is too high and a fault is registered.

Signal Voltage too low:
The signal voltage is compared to a negative threshold value. If the voltage falls below this negative threshold value, a signal is detected which is too low and a fault is registered.






14.16.3 Sensor Signal irrational, P2138

Monitoring Strategy
The signals of the two Hall-effect sensors are compared to each other.

Typical Enable Conditions
- Signal voltage sensor 1 > defined threshold value
- Signal voltage sensor 2 > defined threshold value

Malfunction Criteria
The signal voltage values of sensor 1 and sensor 2 change continuously with the position of the pedal. While doing so, the gradient of the characteristic pedal curve 1 is double the gradient of the characteristic pedal curve 2. The difference between these two signal voltage values is continuously calculated, with the value of the signal voltage of sensor 1 being divided by 2. If the absolute value of this difference is greater than a defined threshold value, an irrational sensor signal is detected and a fault is registered.




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