Throttle Position TP Sensors

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Chapter 13
Throttle Position (TP) Sensors
Automotive Fuel and Emission Control Systems
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Whats its purpose?

• Converts throttle valve angle into an electrical
  signal
• Provides PCM with information on
• throttle opening
• rate of change

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Why?

• electronic accelerator pump
• engine mode
• idle
• part throttle
• wide open throttle (WOT)

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Why?

• clear flood mode
• shift points
• wide open throttle (WOT) a/c operation and
  emission controls
• backs up other sensors

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What is it?

• potentiometer electronic component which has a
  user-adjustable resistance
• a potentiometer converts mechanical movement into
  a variable voltage signal
• usually connected to PCM with a three wire
  harness

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How does it work?

• terminal A reference voltage from PCM
• terminal C return path to ground
• terminal B connects to a moveable wiper that
  sweeps across the resistor and returns a variable
  voltage signal

a typical TPS schematic
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THROTTLE POSITION SENSOR (TPS)CIRCUIT
TOYOTA COURSE 852 ENGINE CONTROL SYSTEMS
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TPS WITH IDLE CONTACT SWITCHCIRCUIT

TOYOTA COURSE 852 ENGINE CONTROL SYSTEMS
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TPS IN THE ETCS-i SYSTEM
TOYOTA COURSE 852 ENGINE CONTROL SYSTEMS
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What can happen?

• incorrect adjustment
• PCM may assume throttle is open and not control
  idle speed
• PCM may not see WOT and prohibit maximum engine
  output
• automatic transmission shift points
• erratic or intermittent signal can cause surge,
  sag or stall
• PCM incorrect information incorrect air/fuel
  ratio increased emissions

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On Board Diagnostics (OBD)

• OBD 1 vehicles use 10/90 rule for monitoring
  sensor integrity
• signal voltage gt 10 of reference DTC
• signal voltage lt 90 of reference DTC
• OBD 2 vehicles use rationality strategy
• PCM compares information from other sensors to
  determine sensor integrity

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Test twice, repair once

• DVOM testing
• key on engine off
• backprobe connectors
• open throttle with accelerator pedal

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• measure voltage between signal wire and ground at
  sensor
• signal should be low at idle
• slowly increase throttle opening
• signal should be high with throttle wide open

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How do we fix it?

• Always follow manufacturers procedures for
  testing sensors and diagnosing DTCs

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Take a picture of it

• oscilloscope testing
• a visual voltmeter with a clock
• shows an image of the signal over a period of
  time

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A dropout or glitch
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Chapter 13
Throttle Position (TP) Sensors

• CHAPTER SUMMARY
• A throttle position (TP) sensor is a three-wire
  variable resistor called a potentiometer.
• The three wires on the TP sensor include a 5-volt
  reference voltage from the PCM, plus the signal
  wire to the PCM, and a ground, which also goes to
  the PCM.
• The TP sensor is used by the PCM for clear flood
  mode, torque converter engagement and release,
  automotive transmission shift points, as well as
  for rationality testing for the MAP and MAF
  sensor.
• The TP sensor signal voltage should be about 0.5
  volt at idle and increase to about 4.5 volts at
  wide-open throttle (WOT).
• A TP sensor can be tested using a digital
  multimeter, a digital storage oscilloscope (DSO),
  or a scan tool.

Automotive Fuel and Emission Control Systems