Common Sensors Understand the following sensors: Pull Up sensor Pull Down sensor Potentiometer Thermistor
Pull Up Switch (sensor) VERY low current 12 volt
Pull Up Switch (sensor) VERY low current 12 volt 12 volt
Pull Down Switch (sensor) VERY low current
Pull Down Switch (sensor) VERY low current
Test the Switch - Sensor Check Scan tool PID data for sensor Should show ON/OFF or Open/Closed as you operate the switch IF No change, check voltage at switch Look for open /shorted wires (use voltmeter and logic to see if wire is open or shorted)
Potentiometers A potentiometer is a Position sensor
Very low current Potentiometer 4 volt
Used as a sensor Potentiometer 2 volt
poor ground Potentiometer 2.5 volt (should be 2 volt)
open ground Potentiometer 5 volt (should be 2 volt)
Potentiometers sense motion check for: reference voltage good ground un-interrupted signal
0.52 V MIL lamp lit. TPS code What is wrong?
0.0 V MIL lamp lit. TPS code What is wrong?
Thermistors Thermistors change resistance with temperature Negative Temperature Coefficient thermistors decrease in resistance when they heat Commonly used to sense changing temperatures
High Resistance when Cold!
Low Resistance when Hot!
Hot or Cold? COLD! 4.52 V
Hot or Cold? HOT! 1.53 V
1.15 1.45 V Poor gas mileage, runs rich, may set oxygen sensor code
0.49 V Poor gas mileage, runs rich, may set oxygen sensor code
0.02 V Poor gas mileage, runs rich, may set oxygen sensor code
Thermistors Thermistors are checked with an Ohmmeter or a Voltmeter A temperature probe or thermometer should be used when checking Compare temperature at measures at sensor temperature displayed on Scan Tool
Semiconductors Elements with four valence electrons are not good as insulators or conductors Silicon, when is a crystal form, shares valence electrons to make a good insulator Silicon can be doped to add electrons to the valence ring or remove electrons from the valence ring
Semiconductors Silicon doped with phosphorous (which has five electrons in the valence ring) will create an N type semiconductor Silicon doped with boron (which has three electrons in the valence ring) will create a P type semiconductor
Semiconductors All Semiconductors will be destroyed by: Too much Current Too much Voltage
Diodes Placing an N type semiconductor with a P type will create a diode. In a forward biased diode current will flow with a small amount of resistance Too much current will overheat and destroy the diode
Diodes Reverse biasing a diode will create very high resistance at the center of the diode and current will not flow Too much voltage will overcome the internal resistance and the diode will short out
12.6 V Arrow shows conventional theory (hole flow) Diodes wired like this will block current
0.0 V Arrow shows conventional theory (hole flow) Diodes wired like this will block current
12.6 V Arrow shows conventional theory (hole flow) Diodes wired like this will allow current to flow with a slight voltage drop
12.0 V Diodes use (Drop) about.5 volts Arrow shows conventional theory (hole flow) Diodes wired like this will allow current to flow with a slight voltage drop
0.1 V Arrow shows conventional theory (hole flow) Diodes wired like this will allow current to flow with a slight voltage drop
Testing Diodes Diodes require.2 -.6 volts to forward bias Digital ohmmeters may not supply this voltage with ohm check use diode check feature when using DVOM
Testing Diodes Shorted diodes on alternators will allow A/C voltage that may confuse a control module Routine checks with oscilloscope are easy
Anti- Spike Diodes Clamping or Anti-Spike diodes protect sensitive control modules from...too much VOLTAGE
Semiconductors All Semiconductors will be destroyed by: Too much Current Too much Voltage
Failure in Anti- Spike Diodes An open, or shorted diode will damage computer control modules Shorted relay coil windings will cause too much current to flow and burn out switching transistors in computers Shorted Diodes allow too much current Check resistance with an OHM meter
Failure in Anti- Spike Diodes An open, or shorted diode will damage computer control modules Open diodes allow spike voltages to harm electronic components (too much VOLTAGE) Oscilloscope will show an OPEN diode for any coil
Types of Diodes Positive diode Negative diode Zener Diode Light Emitting Diode (LED)
Transistor acts like a very fast On/Off pull down switch
Transistors Transistors can act as a relay they use a small signal current to control a larger working current Transistors can act as a signal amplifier
PNP transistor Points InPermanently Will conduct current when the base sees a Negative polarity
NPN transistor Never Points In Base must be Positive to allow transistor to conduct current
Transistors can act as a Signal Amplifier Small changes in current flow through the Base will result in large current flow changes through the Emitter and Collector
Transistors Transistors are damaged by too much current check resistance of the LOAD (The load is what is being turned ON or OFF) Transistors are damaged by high voltage Coils turning OFF create high voltage Charging systems that allow Overcharging can damage control modules and computers
Diagnose Control Modules Electronic control modules can not be directly tested Before replacing, verify proper operation of Power Ground Sensors (inputs) Actuators (outputs) Remember Electronics are damaged by high voltage high current
Diagnose Control Modules