Description

Throttle Position Sensor Description

1. Fault Codes:
Throttle Position Sensor - Low out of range P0122
Throttle Position Sensor - High out of range P0123
Throttle Position Sensor - Signal error fault P0121

2. Monitoring Procedure

Summary
Problems with the throttle potentiometer will be detected using a range test.
If this test is not passed then the appropriate fault count will be incremented, otherwise it will be decremented. If the count reaches a given threshold then a fault is present.

Range check.
A voltage being read from the sensor will be compared to upper and lower limits TPOT DIAG MAX VOLTAGE and TPOT DIAG MIN VOLTAGE. If the voltage is outside these limits then a fault counter will be incremented, if not then the counter will be decremented until zero. If the value of the fault counter reaches the limit value TPOT DIAG FAULT LIMIT then a range fault is present, the fault will remain present until the counter reaches zero. The test for maximum voltage will not be performed at high engine loads as full throttle can cause the maximum voltage to be read. The load threshold below which this test can be performed is TPOT DIAG MAX TEST LOAD. Also the fault counter will not be incremented until all of the required conditions for maximum voltage test to fail have been present for greater than a time TPOT DIAG RANGE DELAY.

Signal Error Fault
The system calculates a value for the current air mass flow rate through the engine based on the throttle signal, engine rpm, air temperature and ISCV position. This estimate is compared to the real measured air mass flow rate. If the difference between the two values is greater than a given percentage, then a fault counter is incremented. If the difference is less, then the fault counter is decremented. A different percentage limit is applied in each direction (estimate > actual and actual > estimate).

3. Primary Detection Parameter
Throttle volts - measured in volts, the output of an Analogue to Digital converter circuit.

4. Fault Criteria Limits
Throttle Position Sensor - Low out of range 40mV
Throttle Position Sensor - High out of range 4V
Throttle Signal Error (Lower than actual) 300 %
Throttle Signal Error (Higher than actual) 450 %

5. Monitoring Conditions
The low range check will take place whenever there is power to the ECU; the high range check will take place when the engine speed and load is above & below prescribed threshold respectively; and the system is in a steady state condition.
The signal errorcheck is performed at steady state conditions when both engine speed and engine load are above respective thresholds.
TPOT DIAG MAX TEST LOAD, defined in units of air per stroke:
16%
TPOT DIAG RANGE DELAY allows engine load to rise after snap opening of the throttle:
2 seconds
TPOT DIAG FAULT LIMIT, required no. of fault events to flag a fault:
40
TPOT DIAG XCHK SPEED THRESH, used in signal error check:
600rpm
TPOT DIAG XCHK LOAD THRESH, used in signal error check:
9.9 %

6. Monitoring Time Length / Frequency of Checks
The frequency if the throttle potentiometer diagnostic is 40Hz.

7. Criteria for Storing Fault Code.
Two successive trips where the throttle potentiometer monitoring system indicates a failed potentiometer.

8. Criteria for Illuminating MIL
Two successive trips where the throttle potentiometer monitoring system indicates a failed potentiometer.

9. Criteria for Determining Out of Range Input Signals
The throttle potentiometer is subject to a minimum and maximum voltage limit of 40mV and 4.0V respectively.