Theory Of Operation

The Electronic Throttle Control (ETC) system uses two Throttle Position Sensors (TPS) to monitor the throttle blade position. TPS 1 and TPS 2 are located within the Throttle Body Assembly. The sensors share a common 5-Volt Reference circuit (Supply) and a common Sensor Ground but each sensor has its own Signal circuit (TPS 1 and TPS 2). Each Signal circuit provides the Powertrain Control Module (PCM) with a signal voltage proportionate to throttle blade movement. Normally operating sensor signals are opposing to each other in the following manner:

• TPS 1  voltage starts low, approximately 0.5 volts at closed throttle,  and increases to approximately 4.3 volts at wide open throttle  .
• TPS 2  voltage starts high, approximately 4.5 volts at closed throttle,  and decreases to approximately 0.7 volts at wide open throttle  .

THROTTLE POSITION SENSOR CORRELATION DIAGNOSTIC:  Below are examples of how the PCM checks the TPS calculation for any correlation issues by comparing the Absolute Difference between the two TPS signals. Example 1 is showing a sensor correlation that is within specifications and example 2 is a sensor correlation that is outside of specifications. A simple way to calculate the Absolute Difference is to add TPS 1 and TPS 2 voltage values together. The sum of the two values should equal 5.0 volts +/- 0.25 volts. If the sum of the two values is less than 4.75V, or more than 5.25V, the correlation DTC will set.

• EXAMPLE 1:  Using the voltage readings from the example table below for a NORMAL SENSOR  at CLOSED THROTTLE  :
  • Add TPS 1 (0.542V) + TPS 2 (4.456V) = 4.998V for an Absolute Difference of (-0.002). This is a good sensor correlation reading because the difference between 5.0V and 4.998V is less than the +/- 0.25 volt threshold.
• EXAMPLE 2:  Using the voltage readings from the table below for a FAULTY SENSOR  at CLOSED THROTTLE  :
  • Add TPS 1 (0.252V) + TPS 2 (4.456V) = 4.708V for an Absolute Difference of (-0.292). This is a failed sensor correlation reading because the difference between 5.0V and 4.708V is more than the +/- 0.25 volt threshold.