Module 11 Input
Acknowledgements General Motors, the IAGMASEP Association Board of Directors, and Raytheon Professional Services, GM's training partner for GM's Service Technical College wish to thank all of the people who contributed to the GM ASEP/BSEP curriculum development project 2002-3. This project would not have been possible without the tireless efforts of many people. We acknowledge: The IAGMASEP Association members for agreeing to tackle this large project to create the curriculum for the GM ASEP/BSEP schools. The IAGMASEP Curriculum team for leading the members to a single vision and implementation. Direct contributors within Raytheon Professional Services for their support of translating a good idea into reality. Specifically, we thank: Chris Mason and Vince Williams, for their leadership, guidance, and support. Media and Graphics department under Mary McClain and in particular, Cheryl Squicciarini, Diana Pajewski, Lesley McCowey, Jeremy Pawelek, & Nancy DeSantis. For their help on the Engine curriculum volume, Subject Matter Experts, John Beggs and Stephen Scrivner, for their wealth of knowledge. Finally, we wish to recognize the individual instructors and staffs of the GM ASEP/BSEP Colleges for their contribution for reformatting existing General Motors training material, adding critical technical content and the sharing of their expertise in the GM product. Separate committees worked on each of the eight curriculum areas. For the work on this volume, we thank the members of the Engine committee: Jamie Decato, New Hampshire Community Technical College Lorenza Dickerson, J. Sargeant Reynolds Community College Marvin Johnson, Brookhaven College Jeff Rehkopf, Florida Community College at Jacksonville David Rodriguez, College of Southern Idaho Paul Tucker, Brookdale Community College Kelly Smith, University of Alaska Ray Winiecki, Oklahoma State University - Okmulgee
Contents Module 11 Module s Acknowledgements... 2 Introduction... 4 Objectives... 4 General Operation... 5 Signal Types... 6 Circuit Construction... 7 Circuit Operation... 8 PCM Inputs... 13 Heated Oxygen Sensor (HO2S) Circuit... 16 Intake Air Flow Measurement... 19 Ignition Reference Signals... 22 A/C System Signal Inputs... 27 Power Steering Pressure (PSP) Switch... 29 Automatic Transmission Inputs... 30 Traction Control Desired Torque Request... 31 Theft Deterrent Fuel Enable... 31
Introduction NATEF Standards VIII. Engine B. Computerized Engine Controls Diagnosis and Repair 6. Inspect and test computerized engine control system sensors, powertrain control module (PCM), actuators, and circuits using a graphing multimeter (GMM)/digital storage oscilloscope (DSO); perform necessary action. P-1 7. Obtain and interpret scan tool data. P-1 8. Access and use service information to perform step-by-step diagnosis. P-1 STC Standards ALL Competencies for Electrical Stage 3 18043.03 W B. Automotive Computers 4 Identify types of computer input signals 5 Identify automotive data input sensors 6 Identify cautions to be observed when testing sensors A-8 Competencies for GM Powertrain 16044.10 W/D/H F. PCM Engine Control Management 1 Identify and list the sensors that provide PCM inputs 2 Describe each sensors that provides PCM inputs Objectives Upon successful completion of engine performance module 11, the ASEP student will be able to: Describe sensor signal types Explain sensor circuit construction Explain sensor circuit operation Explain PCM operating parameter operation Verify sensor circuit operation 11-4
General Operation In order to make operating decisions, the PCM depends on information from a network of sensors, switches, and other modules located throughout the vehicle. The information from these items is considered inputs to the PCM. Sensors A sensor provides an electrical output that can be calibrated. Information is supplied to the PCM by sensors that monitor the operating environment and vehicle conditions. These sensors include Engine Coolant Temperature sensor, Vehicle Speed sensor, Intake Air Temperature sensor, Throttle Position sensor, and others. The PCM feeds the information provided by the sensors to the microprocessor. The microprocessor then uses this information and the vehicle specific information in the PROM to calculate desired powertrain operation. The electrical outputs from the PCM command devices (fuel injectors, spark timing, canister purge valve, EGR valve, etc.) to change operating conditions. Figure 11-1, PCM Input Parameters (Typical) 11-5
Signal Types Sensors can be categorized in a variety of ways. One method is by the type of signal the sensor produces. There are three types of sensor signals. Analog Signal Analog signal have continuously varying voltage. Since the PCM is a digital computer it cannot make calculation with analog information; it must first be converted to digital information. To do this the PCM passes all analog input signals through an analog-to-digital converter (A to D converter) before being sent to the microprocessor. Figure 11-2, Analog Signal Digital Signal Digital signals consist of two conditions, HI and LO. A LO signal is 0 volts and a HI signal can be 5 or 12 volts, depending on the circuit. The microprocessor can use this information directly. Figure 11-3, Digital Signal Time Base Signal Some signals must be correlated with time to have a meaning. The microprocessor has a high-speed clock input for time measurement. Some of the signals that require a time reference are obvious: engine speed (rpm) and vehicle speed (VSS). However, one that is not so obvious is the oxygen sensor. 11-6
Circuit Construction Another method of categorizing sensors is by the location of the circuit's source voltage and ground. Circuit voltage and ground can be internal or external to the PCM. The microprocessor determines the state of a sensor input by measuring the input voltage. To understand a PCM circuit you should think of the microprocessor as a voltmeter measuring the sensor input. Schematics in Service Information (esi) show sensor inputs connected to either a voltage source or to a ground; either case, the schematics also show a resistor in the PCM. The voltmeter measures the voltage drop across this resistor. If the sensor input to PCM is connected to the voltage source for the sensor, the PCM reads the voltage source minus the amount that the sensor has reduced the voltage. Pull-Down A "pull down" circuit is provided with a reference voltage signal from the PCM. The power source for the circuit is internal to the PCM and the signal voltage is pulled low by the sensor to an external ground. Figure 11-4, Pull-Down Circuit Pull-Up A "pull-up" or "push-up" circuit has a power source outside the PCM. The PCM does not provide the reference voltage signal. The PCM provides the circuit ground through an internal resistor. Figure 11-5, Pull-Up Circuit 11-7
Circuit Operation The final method of categorizing sensors is sensor circuit operation. There are five methods of circuit operation. These five methods are: discrete input, temperature input, position/pressure input, voltage generator, and signal generator. Although each of these circuits provide a voltage signal to the PCM the difference is the kind of information the circuit is providing and how the PCM interprets it. Discrete Input The simplest kind of signal the PCM receives is known as a "switched" input. A switched input is either a HI or LO signal depending on whether the switch is open or closed and whether it is a push-up or a pull-down circuit. In a "pull-down" circuit the power source for the circuit is internal to the PCM. When the switch is closed; signal voltage is pulled low to an external ground. The PCM registers a low voltage reference signal. When the switch is open, the PCM registers a high reference signal. Figure 11-6, Pull-Down Switch Circuit A "pull-up" circuit has a power source outside the PCM. When the switch is closed, external source voltage generates a high reference signal to the PCM. An open switch, on the other hand, generates a low reference signal. Figure 11-7, Pull-Up Switch Circuit 11-8
Temperature Input A temperature sensor is an inverse temperature coefficient thermistor. The resistance of the temperature sensor varies predictably with temperature change. At low temperature it has high resistance (100,700 ohms @ -40 deg F/C) and at high temperature it has low resistance (177 ohms @ 212 deg F/100 deg C). The PCM supplies a 5 volt reference and ground for the temperature sensor. The sensor input is measured across the resistor at the voltage source. With temperature low, the thermistor's resistance is high and very little current flows through the thermistor; the sensor input close to the reference voltage. When the temperature is high, the thermistor's resistance is lower; most of the reference voltage is dropped across the PCM's internal resistor and the sensor input voltage is about 1.5 to 2 volts. Figure 11-8, Temperature Sensor Circuit 11-9
Position/Pressure Input Although a Position sensor and a Pressure sensor are internally constructed differently, both have identical circuits that operate similarly. The three-wire sensor (potentiometer) has a 5 volt reference, a ground circuit back to the PCM and a signal voltage wire. Depending on the position/pressure, the signal voltage at the PCM varies between a low voltage (0.5v) and a high voltage (4.5v). Figure 11-9, Position/Pressure Sensor Circuit 11-10
Voltage Generator Voltage generator sensors are sensors that produce a voltage signal. The PCM is looking at the quantity or voltage level of the signal. The PCM usually looks at the voltage with regard to a reference level. The Oxygen sensor is an example of this kind of senor. Figure 11-10, Voltage Generator Circuit 11-11
Signal Generator Signal generator sensors are sensors that generate a timed voltage signal. The PCM is looking at the frequency or timing of the signal. The Mass Air Flow sensor is an example of this type of sensor. Figure 11-11, Signal Generator Circuit 11-12
PCM Inputs Engine Coolant Temperature (ECT) Sensor The Engine Coolant Temperature sensor, or ECT, is a two-wire sensor. It is threaded into the engine coolant jacket, in direct contact with the engine coolant. The coolant sensor contains a thermistor and provides the PCM with an engine coolant temperature reading. The PCM provides a five-volt signal to the ECT sensor through a dropping resistor. When cold, the sensor provides high resistance, which the PCM detects as a high signal voltage. As the engine warms up, the sensor resistance becomes lower, and the signal voltage drops. Approximate resistance values are shown in the accompanying chart. At normal engine operating temperature, 85 o C Celsius to 105 o C, the signal voltage is in the range of 1.0v to 2.0v. The PCM uses information about coolant temperature to make the necessary calculations for fuel delivery, ignition control, knock sensor system, idle speed, torque converter clutch application, canister purge, exhaust gas recirculation, and cooling fan operation in some applications. Figure 11-12, Engine Coolant Temperature (ECT) Sensor 11-13
Intake Air Temperature (IAT) Sensor The Intake Air Temperature sensor, or IAT, is a two-wire sensor positioned in the engine air intake to register the temperature of incoming air. Like the coolant temperature sensor, the IAT sensor is a thermistor device, which provides a varying voltage signal depending on resistance. Its resistance decreases as temperature increases. The PCM supplies a fivevolt signal to the IAT through a dropping resistor. Sensor resistance and the resulting sensor voltage are high when the sensor is cold. As temperature rises, resistance and sensor voltage go down. Air temperature readings are of particular importance during open loop, or cold engine operation. A reading of manifold, or intake air temperature is needed by the PCM to: Adjust the air fuel ratio in accordance with air density Modify spark advance and acceleration enrichment Determine when to enable EGR on some applications. Figure 11-13, IAT Sensor Circuit 11-14
Throttle Position (TP) Sensor The Throttle Position, or TP sensor, is a three-wire, variable resistor mounted to the throttle body and operated by the throttle valve shaft. When the throttle is closed, the PCM reads a low voltage signal. When the throttle is wide open, the PCM reads a high voltage signal. The voltage signal changes relative to the throttle position, about 0.5v at idle and about 4.5v at wide open throttle. Information from the T P sensor concerning throttle plate angle is one parameter used by the PCM to calculate fuel delivery, ignition timing, and transmission shifting schedule, EGR, torque converter clutch application, upshift light operation, and the evaporative emission control system. Figure 11-14, Throttle Position Sensor Circuit 11-15
Heated Oxygen Sensor (HO2S) Circuit The Heated Oxygen Sensor, or HO2S, is unique among the engine control system sensors because it acts like a battery and is able to generate its own low voltage signal. It is located in the exhaust system and monitors the amount of oxygen in the exhaust stream. It provides feedback to the PCM, which uses this information to manage fuel delivery. The electrically heated oxygen sensor warms up quickly and remains hot, even at idle when the exhaust manifold may cool down. Construction The HO2S has a center element made of a ceramic material called Zirconia. There are two platinum electrodes, which make up the inner and outer surfaces of the center element. The inner surface of the sensor is exposed to outside air. This surface forms the positive terminal of the HO2S circuit. The platinum coating on the outside of the sensor element is exposed to exhaust gases. The gases heat up the HO2S and keep it at the correct operating temperature of 600 degrees Fahrenheit. The outer surface forms the negative terminal of the sensor circuit. The HO2S generates an electrical signal as the result of the interaction of outside air, the inner surface of the element, exhaust gases, and the outer surface of the element. Figure 11-15, Oxygen Sensor 11-16
Operation The PCM applies a reference voltage, also known as bias voltage, of 450 mv to the HO2S. The PCM compares this reference voltage with the voltage generated by the HO2S. The amount of voltage the HO2S generates is proportionate to the difference between the amount of oxygen in the outside air and in the exhaust gases. The atmosphere contains about 21% oxygen. The exhaust from a rich air fuel ratio contains almost no oxygen. With a large difference between the amounts of oxygen contacting the two surfaces, the sensor is able to generate more voltage. When the exhaust gas is rich, below 14.7:1, the voltage output is high, above 450 mv. Figure 11-16, Different Oxygen Levels The exhaust with a lean air fuel ratio has about 2% oxygen. With a smaller difference between the amounts of oxygen on the two surfaces, the sensor generates less voltage. When the exhaust gas is lean, above 14.7:1, air fuel ratio, the sensor's voltage output is low, below 450 mv. In either case, the PCM reads the difference and adjusts injector operation to make the air fuel ratio richer or leaner as required. 11-17
In a normally operating engine, the HO2S output voltage constantly fluctuates up and down between 100 mv and 900 mv. This fluctuation reflects the changes in the air fuel ratio. The PCM adjusts injector pulse width in response to the changing HO2S signals. This data is used to determine short term and long term fuel trim. Figure 11-17, HO2S Voltages HO2S output voltage constantly fluctuates up and down and is used for: Adjusting injector operation Determining short term and long term fuel trim Open loop/closed loop criteria EGR diagnostics Monitoring catalyst efficiency Secondary air and EVAP diagnostics 11-18
Intake Air Flow Measurement There are two methods of sensing incoming engine air flow: speed density and mass air flow. The PCM uses intake air flow measurement information for: Barometric pressure readings Fuel delivery (enrichment, enleanment, fuel cut-off) Spark calculations Diagnostics Speed Density Speed Density is a system of measuring intake air flow by sensing changes in intake manifold pressures which result form engine load and speed changes. The PCM uses a MAP sensor to read manifold absolute pressure. The PCM combines MAP along with temperature, RPM, estimates of volumetric efficiency an EGR to calculate mass air flow. As manifold pressure increases, air density increases as well and additional fuel is required. The PCM increases injector pulse width to meet this requirement based on a "calculated" air flow. Figure 11-18, Map Sensor, Speed Density System 11-19
Manifold Absolute Pressure (MAP) Sensor The Manifold Absolute Pressure (MAP) sensor is a three wire sensor located in the engine compartment. The MAP sensor measures changes in intake manifold air pressure. MAP is low when vacuum is high, and MAP is high when vacuum is low. When the engine is not running, the manifold is at atmospheric pressure, and the MAP sensor is registering barometric, or BARO, pressure. BARO readings are used for fuel delivery calculations at start up, and fuel and spark calculations when the engine is running. The PCM updates its BARO reading when the ignition is turned on and when the throttle is wide open. The MAP sensor currently being used on GM vehicles is a Strain Gauge type. This sensor contains a silicon chip, approximately three millimeters square. It is placed in a sealed housing, which is connected to the manifold. A fixed pressure is sealed above the silicon chip with manifold pressure below it. When the engine is running and manifold vacuum is created, the pressure below the chip drops, creating a change in resistance. During operation, constantly varying vacuum from the intake manifold is applied to the sensor housing. Any change in applied vacuum causes a corresponding change in the sensor's resistance. Electrically, when manifold pressure is low, the sensor voltage is low. When manifold pressure is high, sensor voltage is high. Figure 11-19, MAP Sensor Circuit 11-20
Mass Air Flow A Mass Air Flow (MAF) sensor is positioned in the intake air duct or manifold. It measures the volume and density of the incoming air. The MAF sensor is able to take the temperature, density, and humidity of the air into account. All of these variables together determine the mass of the incoming air. The PCM reads actual mass airflow to calculate fuel requirements. Mass Air Flow (MAF) Sensor GM has used several types of MAF sensors. All use the same operating principle: the resistance of a conductor varies with temperature. In the case of the MAF sensor, the conductor is maintained at a constant calibrated temperature. As a greater volume of air passes the heated conductor, the passing air carries heat away. More current is required to maintain the constant temperature of the conductor. In a similar manner, if the air is more humid, denser, or cooler, it will absorb more heat from the sensor, requiring more current to maintain the temperature of the sensor. This current then translates into a voltage signal, telling the PCM how much airflow there is, so that the PCM can make fuel delivery and spark timing calculations. Figure 11-20, Hot Wire Mass Air Flow Sensor Circuit 11-21
Ignition Reference Signals Distributor Ignition (DI) or Electronic Ignition (EI) reference signals are an indication from the ignition system of engine speed. These signals are sent on the reference circuit from the ignition module to the PCM. On engines with an HEI distributor, the DI module receives signals from the pickup coil assembly in the distributor and sends them on to the PCM on the RPM reference wire. On distributorless engines, the ignition module receives signals from the crankshaft position sensor located either in the engine block or on the front of the engine, depending on application. This signal is then sent to the PCM as a 5-volt digital signal. The PCM requires ignition reference pulses in order to control: Spark timing Triggering and synchronization of fuel injectors Idle Air Control (IAC) valve operation Fuel pump relay EGR Canister purge (EVAP) Figure 11-21, Ignition Reference Circuit 11-22
Crankshaft Position Sensor The crankshaft position sensor (CKP), is the most critical input for the ignition system. It identifies cylinder pairs at top-dead-center. The PCM uses the camshaft (CMP), sensor to identify which cylinder is on the compression stroke and which is on exhaust. Camshaft Position Sensor While the CKP sensor identifies cylinder pairs at top dead center, the CMP sensor identifies cylinder stroke. The CMP sends a signal to the PCM, which uses it as a sync pulse to trigger the injectors in proper sequence. The PCM uses the CMP signal to indicate the position of the number one piston during its intake stroke. This allows the PCM to synchronize the ignition system and calculate true Sequential Fuel Injection (SFI). Figure 11-22, 4.3L Ignition System 11-23
Vehicle Speed Sensor (VSS) The vehicle speed sensor (VSS), provides vehicle speed information to the PCM. The PCM needs information about vehicle speed to operate: The idle air control valve Canister purge Torque converter clutch Cruise control Transmission shift solenoids Electric cooling fans. The magnetic VSS consists of a permanent magnet generator, which produces an AC voltage whenever vehicle speed is over three miles per hour. The AC voltage level and the number of pulses increase with vehicle speed. Since the VSS output is AC voltage, which cannot be directly used by digital electronic components like the PCM, the AC voltage is converted into a digital signal by the VSS buffer. Figure 11-23, Magnetic VSS Buffer Amplifies 11-24
Knock Sensor System The Knock Sensor system allows the PCM to control ignition timing for the best possible performance while protecting it from potentially damaging detonation. The Knock Sensor is used to detect engine detonation, or knock, and signal the PCM to retard ignition timing. The PCM supplies a five-volt reference signal to the knock sensor through a dropping resistor. Since the knock sensors have internal resistance, a voltage drop is created and read by the PCM to determine if the circuit is open, shorted to ground, or shorted to voltage. The Knock Sensor sends the PCM an AC voltage signal when detonation occurs. The PCM processes the signal and modifies the ignition timing to control knock. When the Knock Sensor signal stops, the PCM begins to return the ignition timing in two to four degree increments back to normal IC advance. The Knock Sensor allows the PCM to advance ignition timing as much as possible for the best performance and fuel economy. But perhaps more important, the Knock Sensor controls ignition timing to protect the engine when low octane fuel is being used. High engine temperatures and potentially damaging detonation are more likely with the use of low octane fuel. On some systems, the Knock Sensor system has a built-in self-test mode. Once per engine start-up, during certain engine conditions, the ignition is advanced intentionally to induce a knock, which the Knock Sensor should detect. This self-test is bypassed if a knock occurs and is detected before the conditions are met to run the self-test. Figure 11-24, Integrated KS System 11-25
Fuel Tank Pressure Sensor The fuel tank pressure sensor is used to detect leaks in the evaporative emissions system. The sensor is a three-wire strain gauge sensor, much like the common MAP sensor. However, this sensor measures the difference between the air pressure, or vacuum, in the fuel tank and the outside air. The fuel tank pressure sensor mounts at the top of the fuel tank sending unit and alters the reference voltage to create a signal voltage. The sensor's seal at the sending unit is critical and should be inspected whenever the sensor is removed or serviced. Ceramic Resistor Card Fuel Level Sensor Beginning with some 1996 Enhanced EVAP equipped models, the fuel level sending unit was switched from a wire wound 0-90 ohm potentiometer to a ceramic card resistor 40-250 ohm potentiometer. The improved resolution improves fuel level sensing accuracy, needed when the PCM performs on-board diagnostic tests. The ceramic card assembly consists of a: Ceramic card Wiper arm Float arm assembly Wire harness assembly. Figure 11-25, Ceramic Resistor Card Fuel Sensor The sensor is used to convert changes in the fuel tank level to a variable electrical signal used to drive a gauge in the instrument cluster. The ceramic resistor card fuel level sensor attaches to the outside surface of the modular fuel sender assembly. An electrical harness attached to the fuel sender cover connects the ceramic resistor card to the vehicle wiring harness. Power to the sensor is received from the PCM. The float and float arm assembly work in conjunction with the resistor to measure fuel level. A full tank of fuel forces the float to the top position. With little or no fuel, the float moves to the bottom of the tank. The function of the ceramic resistor card is to vary the resistance of the signal from the PCM, depending on the position of the float. The resistance signal is determined by the wiper contact's position on the conductive bars of the ceramic resistor card. The fuel gauge converts the PCM signal into the fuel level reading on the instrument panel. 11-26
A/C System Signal Inputs There is no specific sensor for the Air Conditioning (A/C) request. Instead, the input comes to the PCM from the A/C control head on the instrument panel. When the A/C system is turned on, the A/C compressor puts a sudden load on the engine. This could lead to driveability problems such as stalling, especially at idle. To prevent this, the A/C switch does not control the A/C compressor directly. Instead, the switch sends an A/C request to the PCM. Depending on the engine control system and engine operating conditions, the PCM does a number of things: Including delaying A/C clutch engagement after A/C is requested Adjusting idle RPM to compensate for the extra load Disengaging the A/C clutch during wide-open throttle operation. There are a number of other A/C system switches that must be closed for this to happen. These may include a high-pressure switch and or a lowpressure switch. These switches may be in series with the A/C request, or separate inputs to the PCM. Figure 11-26, A/C Systems Inputs 11-27
The PCM can have two additional inputs regarding the A/C system: The Refrigerant pressure sensor, and Evaporator temperature sensor. The A/C refrigerant pressure sensor is a three-wire sensor that responds to changes in system high side pressure. The PCM supplies a five-volt reference and ground. A signal circuit is monitored by the PCM. On most systems, the PCM uses the pressure sensor signal to identify a resulting pressure increase after the PCM has commanded the A/C compressor clutch to engage. On some other systems, this pressure signal is also used to determine IAC valve position for idle speed control. The evaporator temperature sensor, also a three-wire sensor, is used by the PCM to cycle the A/C clutch for optimum cooling. Additionally, the PCM can help prevent evaporator freeze-up by disabling the A/C clutch. 11-28
Power Steering Pressure (PSP) Switch The Power Steering Pressure (PSP), switch is a two-wire, ON/OFF switch, located in the power steering fluid pressure line. It is used to detect high system pressure. The PCM uses this information for: IAC control Spark retard during idle for improved idle stability A/C compressor control. During low vehicle speed operation the power steering system pressure may be high. The added load of the power steering pump could cause the engine to stall. The power steering pressure switch can be either normally open or closed, depending on design. When the calibrated pressure is reached, sensor circuit voltage switches. In response to this signal, the PCM operates the idle air control to increase engine speed slightly. If the vehicle is equipped with air conditioning, the PCM may also turn "OFF" the compressor clutch relay when the PSP switch indicates high pressure. Figure 11-27, Power Steering Pressure (PSP) Switch 11-29
Automatic Transmission Inputs Electronically controlled transmission gear switches are ON/OFF switches, controlled inside the transmission transaxle. Some switches are normally open when the gear is not engaged, and closed when the corresponding gear is engaged. Other switches are normally closed when the gear is not engaged and open when the gear is engaged. Electronically controlled transmissions and transaxles have a Fluid Pressure Switch Assembly (PSA) mounted in the valve body. There are five separate switches that respond to manual valve position. As the switches in the PSA are exposed to the various fluid pressures of the different gear ranges, different switch ON/OFF combinations occur. Three circuits are monitored by the PCM; the different combinations inform the PCM which PRNDL range has been selected, based upon the manual valve position. Figure 11-28, Fluid Pressure Switch Assembly The Transmission Fluid Temperature (TFT) Sensor is either mounted in the PSA or is part of the harness. It is a thermistor, similar to the other temperature sensors used for engine management, which is submersed in the transmission fluid. The TFT sensor's resistance alters the five-volt reference signal sent by the PCM, which uses this signal to help control TCC apply and to control line pressure. At higher temperatures, the PCM can command TCC apply to reduce the temperatures generated by the converter's fluid coupling. 11-30
Traction Control Desired Torque Request On vehicles with traction control, there is constant communication between the Electronic Brake Traction Control Module (EBTCM) and the PCM. The traction control desired torque request is a pwm signal that ranges from 0-100%. The EBTCM reduces the pulse width of the traction control desired torque request when a drive wheel slippage situation is detected. The PCM monitors the traction control desired torque request. If a signal of less than 100% is seen, the PCM, depending on vehicle application, reduces wheel slippage by: Retarding spark timing Closing the throttle Decreasing the boost solenoid pwm Disabling fuel injectors Theft Deterrent Fuel Enable The Theft Deterrent Fuel Enable signal is an input from the Vehicle Theft Deterrent Module. It signals the PCM to enable the fuel injectors. If the Vehicle Theft Deterrent Control Module does not send the correct Theft Deterrent Fuel Enable signal to the PCM, the fuel system may be disabled. On some vehicles, this signal is a direct input to the PCM. Other applications use Class 2 serial data to transmit this message. 11-31