1. Sensor Basics and Computer Operation 1

2.  The fuel pump is typically supplied B+ voltage controlled by a PCM-energized relay.  The pump may be located in the fuel tank, or close to the frame under the vehicle.  It is important to find out if the fuel pump control circuit is functioning before replacing the pump. 2

3.  Testing of the fuel pump should include: ◦ Voltage available test ◦ Ground integrity test ◦ Fuel pressure test  In some applications, being out of specification by as little as 3 PSI can cause a no-start condition.  May include rest pressure test ◦ Fuel volume test ◦ Pressure leak down test ◦ Never deadhead tool pressure test 3

4.  Fuel injectors typically have voltage supplied to them, and the PCM controls the ground for the circuit.  Injectors should be checked for proper resistance and balanced flow.  Injector circuits can be checked using noid lights or specialized test lights. ◦ Refer to OEM testing procedures for detailed guidelines. 4

5. 5  PWM (DIGITAL)  FREQUENCY  ANALOG  ANALOG to DIGITAL

6.  There are several types of air flow sensors in use today. These are typically classified in three different categories. ◦ Hot wire MAF – Based on the principle that the resistance of a conductor varies with temperature. ◦ Vane air flow (VAF) – Based on the principle that air has volume and can rotate an analog sensor plate. ◦ Karman vortex – Based on the principle that air turbulence can affect sound waves. ◦ http://youtu.be/sSuL58YEH-E http://youtu.be/sSuL58YEH-E 6

7.  The PCM can convert the signal from the module into data that directly relates to the amount of airflow entering the engine. ◦ The module may send data to the PCM that is a varying reference voltage which is considered to be analog, or a frequency which is referred to as digital. ◦ MAF data is used by the PCM to determine fuel and timing requirements for the engine. It is a very good indicator of engine load. ◦ Some MAF sensors have a self cleaning function, while others may actually use a hot film instead of a wire. 7 Airflow Sensing

8.  Hot wire MAF sensors are typically suspect if other engine performance tests are inconclusive. ◦ Do not assume a part is bad without performing a diagnostic procedure to prove it.  A hot wire MAF can be diagnosed with a scan tool, a DMM with frequency measuring capabilities, or an oscilloscope. ◦ Follow manufacturers specifications and recommended testing procedures. 8

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10.  Most engine management systems use NTC thermistors for input regarding the temperature of the coolant in the engine and the air entering the engine.  By using precise temperature measurements, engine performance and mixture control can be fine tuned to an extent not possible without them. 10

11.  Temperature sensor circuits utilize two resistors. One with a fixed value in the PCM, and the other is variable and located in the sensor itself.  By using a resistor inside the PCM, if a 5 volt reference wire should accidentally ground, the chance of PCM damage decreases, since the resistor will be able to reduce the amount of current to a level safer for solid state components.  http://youtu.be/i2Kd0VQWw1o http://youtu.be/i2Kd0VQWw1o  http://youtu.be/ZuCVzUarefE http://youtu.be/ZuCVzUarefE 11

12.  Most PCM strategies are developed so that the voltage drop across the temperature sensor is monitored. This voltage is recognized as a specific temperature value by the PCM. ◦ The PCM may use several different temperature sensors on the same car for different functions ◦ Different temperature sensors can easily have different resistance values based on their application. Make sure replacement sensors meet OEM requirements. 12

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14.  Temperature sensors are checked with an ohm meter at specific temperatures, monitored for voltage, and verified with a scan tool for proper operation. 14

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16.  The throttle position sensor is typically a potentiometer mounted on the throttle body opposite the throttle linkage.  In the late 80’s Toyota and Ford began to use Hall Effect TPS. Also, some euro manufacturers  The potentiometer varies a voltage sent by the PCM to be used as an indicator of throttle opening. ◦ Low voltages indicate minimal throttle opening, while higher voltages indicate wider throttle openings.  Check OEM specifications 16

17.  The TPS sensor is typically tested by measuring the voltage signal it is returning to the PCM. This is typically done with a volt meter, a digital oscilloscope, or a scan tool. ◦ TPS sensors are mechanical and prone to wear. This can usually be found as a sudden signal voltage drop or jump as the sensor is rotated slowly.  Generally found at the position the customer keeps the throttle at most frequently. ◦ The customer may describe this as a “buck” or “trailer- hitch” sensation while driving, with no MIL. ◦ http://youtu.be/Ww7xji36i8s http://youtu.be/Ww7xji36i8s 17

18.  A MAP sensor contains a silicon chip in a sealed housing which is connected to the intake manifold, usually through a vacuum line.  Vacuum is sealed above the chip, and manifold pressure is applied under it. ◦ Some MAPs operate similar to a TPS and modify a 5v reference signal from the PCM, based on manifold pressure. ◦ Some MAPs are frequency modulated and return the 5v reference as a frequency to the PCM, based on manifold pressure. 18

19.  If a car is equipped with a MAP, the MAP is not necessary. ◦ Cars equipped with a MAP and no mass air flow sensor are called speed-density systems. They rely on intake air temperature along with other inputs to determine the amount of air in the cylinders for mixture control.  Some cars have a MAF and a MAP, but typically the MAP signal is used only if a failure occurs with the MAF. ◦ This allows the car to run with a MAF failure. 19

20.  Vehicles with MAP sensor failures are prone to a wide variety of running problems. ◦ Black smoke, hard starting, pinging, and stalling can all occur with a MAP malfunction.  MAP sensors are typically checked with a DMM that can measure voltage and frequency (Hz), a hand held oscilloscope, and/or a scan tool. ◦ Follow the procedures outlined by the OEM for your application. 20

21.  In some applications, a sensor very similar in appearance and function to a MAP sensor is utilized by the PCM. It does not, however, have a vacuum line connected to the manifold. It is simply exposed to the atmosphere. In this arrangement, the sensor is known as a Barometric Pressure Sensor, or BARO Sensor.  http://youtu.be/_vAtjLil5Y0 http://youtu.be/_vAtjLil5Y0  http://youtu.be/z40ajpBMWVI http://youtu.be/z40ajpBMWVI 21

22.  There are several components on an automobile that rotate. From crankshafts to camshafts & drive shafts to brake discs. This rotation is monitored by the PCM for RPM, timing, vehicle speed, and traction control to name a few.  Rotation is monitored by the PCM through one of the following three sensors. 22

23.  http://youtu.be/EE84cGHJfKE http://youtu.be/EE84cGHJfKE  http://youtu.be/RtqeOYNgn8A http://youtu.be/RtqeOYNgn8A  http://youtu.be/H5rfWyLSfyI http://youtu.be/H5rfWyLSfyI  http://youtu.be/EE84cGHJfKE http://youtu.be/EE84cGHJfKE 23

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25.  Magnetic pulse generator (Induction sensor) ◦ Consists of a coil of wire, a magnet and a toothed wheel. ◦ As the toothed wheel passes towards or away from the magnet, flux lines are generated that cut through the coil of wire generating a voltage. ◦ This sensor produces an AC voltage and is used for crank position, distributor signals, cam position and a wide variety of other devices.  It is usually tested with a DMM on AC volts, Hz, or ohms (to check the resistance of the wire coil) or an oscilloscope. 25

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27. ◦ The distance between the magnet and the toothed wheel, or “air gap” is a very critical adjustment on this type of sensor.  Adjust the air gap to OEM specifications.  Paper may be used to automatically set the air gap upon installation, it is then torn away by the rotating toothed wheel. ◦ This type of sensor typically has two wires, but in some cases will have three, when a shield is wrapped around the wires to decrease interference. 27

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29.  The hall effect sensor is another type of rotational sensor that produces a DC or square wave signal.  It is comprised of a chip, a magnet and shutter blades. ◦ The magnet acts upon the chip allowing a reference voltage back to the PCM until the lines of force are interrupted by the shutter blades. At that point voltage back to the PCM stops. The frequency at which this occurs is interpreted as a frequency by the PCM for calculating rotational speeds and position. 29

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31.  Hall effect sensors are processed very quickly by the PCM since they do not need to be converted from an analog signal to a digital one. ◦ They are typically tested with a DMM capable of measuring frequency, or an oscilloscope. ◦ While very similar in design, manufacturers do use different testing procedures, so refer to the service manual for the vehicle and system you are working on. 31

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33.  Optical Sensors use LEDs and photo diodes to signal the PCM. A shutter wheel is placed in between them and allows light from the LEDs to act upon or be blocked from the photo diodes.  More than one set of LEDs and photo diodes allow more than one piece of information to go to the PCM at a time. 33

34.  This makes the optical sensor very good at both sensing position and speed simultaneously. ◦ For this reason, they are used to great extent in distributors to determine not only RPM, but camshaft position and piston location.  Optical sensors are tested with a DMM, oscilloscope, or scan tool. ◦ Follow OEM procedures. 34

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36.  Simple or complex mechanical switches can be used for a wide variety of functions from turning on an oil light, to allowing the starter circuit to work.  Switches are used as inputs to relay information. 36

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38.  They can be pressure controlled ◦ Like a power steering pressure switch  They can be linkage controlled ◦ Like a Park/Neutral switch on an automatic transmission  They can be directly controlled ◦ Like the A/C “on” button  Malfunctions in these switches can lead to no- start, stalling and other issues. ◦ The mechanical switch can be simple by design, but has proven difficult to diagnose. 38

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40.  Switches are tested by performing voltage drops, continuity and resistance checks. ◦ Some switches may require components to be activated and deactivated. ◦ Continuity tests and resistance tests on components should be performed the switch disconnected from its electrical connector.  This ensures there is no power to the switch and isolates the switch from the circuit. 40

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42. Inside the computer there is an input conditioning section, a processing section, programming section and an output section. 01152007 E4242

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44. The A/D converter is used to condition the incoming signal from the sensor so that the computer can use it.  Connects sensor to microcomputer  Converts Sensor output to digital signal  May contain amplifier 01152007 E4444

45. The voltage regulator keeps the voltage signal at a steady rate regardless of the battery or charging system voltage.  Supplies lower voltage for computer and sensors  Maintains constant reference voltage to sensors 01152007 E4545

46. The amplifier increases voltage of small or weak input signals so the computer can use them. 01152007 E4646

47. The microprocessor is where all the logical decisions are made. Another term used to describe the microprocessor is “CPU”- Central Processing Unit. 01152007 E4747

48.  IC chip that compares input signals to instructions in memory then sends signals to actuators output components  Has no memory capabilities  Reads information from memory chips  Can write new information into memory 01152007 E4848

49. The memory chip is part of the computer which stores data. Some allow information to be written into them and others are permanent memories where no changes can be made. 01152007 E4949

50. The read only memory (ROM) is used for permanent storage. Information is written into the chip at the time of manufacture. Vehicle operating parameters are programmed into the chip based on the type of vehicle and Powertrain used. 01152007 E5050

51.  Data will not be erased while being used – “read out”  New information cannot be written into ROM chip  Information will not be erased with removal of power supply 01152007 E5151

52. The random access memory (RAM) is used for temporary storage. Information is written to it constantly during vehicle operation.  Also called read and write memory  Information will be lost with removal of power supply  Scratch pad for computer 01152007 E5252

53. The Keep Alive RAM is a portion of the RAM that is kept alive by maintaining battery power to it with the ignition “OFF”.  Used to store start up values ◦ Fuel corrections ◦ Idle ◦ Shift strategies 01152007 E5353

54. The programmable read only memory (PROM) contains information relating to vehicle powertrain requirements Refines or modifies instructions from ROM  Keeps memory if power supply is removed 01152007 E5454

55. The erasable programmable read only memory (EPROM) chip can be reprogrammed by using a light source to erase the information stored in it. It must be removed for modification.  Retains memory without power supply  UV – erasable (few times) 01152007 E5555

56. The electronically erasable programmable read only memory (EEPROM) can be reprogrammed by using a specified voltage applied to specific pins. 01152007 E5656

57.  Information can be written and permanently stored  Flash type - electrically bulk erasable (1000 to 10,000 times)  Data is kept with loss of power 01152007 E5757

58. The clock is used to time the events in the computer. All data is processed in the certain sequence.  Electronic timer  Used to coordinate all operations of computer 01152007 E5858

59. The output device conditions electrical signals that were processed by the microprocessor. They are used to operate the actuators controlling vehicle functions.  Connects microcomputer to control device 01152007 E5959

60.  Converts digital signal to analog signal for actuator use  Output drivers may be used to amplify signal to actuator  Output drivers may be used to control return side of circuit 01152007 E6060

61. You can compare computer operation to yourself. Normally you would collect information (input), analyze the information, refer to tables and charts (processing), act on your decision (output) 01152007 E6161

62.  Processing ◦ Voltage signals “analog” are processed by input device ◦ Converted to digital data  Basic strategy ◦ Used for normal driving conditions 01152007 E6262

63.  Data path (processing) ◦ Digital signals are sent to RAM for momentary storage ◦ Signal may have to be amplified ◦ Microprocessor compares data received in RAM to program in ROM 01152007 E6363

64. ◦ Microprocessor then compares data of RAM and ROM to information in PROM which fine tunes results ◦ Final decisions from CPU are sent to output device to be converted to analog signal and used by actuators 01152007 E6464

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66.  De-multiplexer (DEMUX) is used on output side of CPU  Allows data to travel both directions on same wire – not at same time  May use two wires in a twisted pair arrangement 01152007 E6666

67. 01152007 E6767 POTS TPS EGRP VAF PIEZO MAP BARO KS THERMISTOR CTS IAT MAF HOT WIRE VORTEX VANE O2S ZIRCONIUM TITANIA VSS MAG P/U HALL EFF. OPTICAL CMP CKP MAG P/U HALL EFF. INPUT DEVICE A/D CONV MUX 1 TO MANY MICROPROCESSOR CPU CLOCK ROM PERMANENT GENERAL INFO PROM SPECIFIC INFO WT, DRIVE TRAIN, ETC PERMANENT EEPROM ODOMETER PERMANENT RAM READ / WRITE MEMORY TEMPORARY KAM ADAPTIVE STRATEGY TEMPORARY DEMUX MANY TO 1 OUTPUT DEVICE D/A/CONV TIMING FUEL ADJ. EMISSIONS EGR SOLENOID SUSPENSION CLIMATE CONTROL MOTORS SOLENOIDS RELAYS SENSORSACTUATORS A or D VOLTAGES MAKES DECISIONS AND CALCULATIONS