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. 

The PCM performs multiple diagnostics on the Throttle Position Sensors. Along with the typical circuit high and circuit low diagnostics, the PCM also checks the TPS calculation for any correlation issues. Below is an explanation of how the PCM checks the Absolute Difference between the two sensors:

• The actual algorithm used in the diagnostic is: (TPS 1 value) - (5V - TPS 2 value) should be equal to 0.0V (+/- 0.25 volt error).
• EXAMPLE 1:  Using the voltage readings from the example table below for a NORMAL SENSOR at WIDE OPEN THROTTLE, calculate the Absolute Difference of TPS 1 and TPS 2 as follows:
  • TPS 1 (4.313V) - TPS 2 (5V - 0.698V = 4.302V), or 4.313V - 4.302V = 0.011V.

  This is a good sensor correlation reading because the difference is less than the +/- 0.25 volt threshold.

• EXAMPLE 2:  Using the voltage readings from the example table below for a FAULTY SENSOR  at WIDE OPEN THROTTLE,  calculate the Absolute Difference of TPS 1 and TPS 2 as follows:
  • TPS 1 (3.993V) - TPS 2 (5V - 0.698V = 4.302V), or 3.993V - 4.302V = -0.309V.

  This is a failed sensor correlation reading because the difference is more than the +/- 0.25 volt threshold.

Another easier way of calculating this 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 same voltage readings from as EXAMPLE 1 above for a NORMAL SENSOR  at WIDE OPEN THROTTLE: 
  • Add TPS 1(4.313V) + TPS 2(0.698V) = 5.011V.

  This is a good sensor correlation reading because the difference between 5.0V and 5.11V is less than the +/- 0.25 volt threshold.

• EXAMPLE 2:  Using the same voltage readings from the table above for a FAULTY SENSOR  at WIDE OPEN THROTTLE: 
  • Add TPS 1(3.993V) + TPS 2(0.698V) = 4.691V.

  This is a failed sensor correlation reading because the difference between 5.0V and 4.691V is more than the +/- 0.25 volt threshold.

DISCLAIMER:  The normal sensor voltage readings in the table below are typical readings for a Throttle Body on a 3.6L engine. The voltage values will vary slightly for different engines. THIS IS INTENDED AS AN EXAMPLE  to aid in explaining how the diagnostic performs the Absolute Difference calculation between TPS 1 and TPS 2.