Control Module Inputs and Outputs
AUTOMATIC SHUTDOWN (ASD) SENSE - PCM INPUTIt is an input to the Powertrain Control Module from the rely in the Power Distribution Center, refer to the cover for relay location.
The ASD sense circuit informs the PCM when the ASD relay energizes. A 12 volt signal at this input indicates to the PCM that the ASD has been activated. This input is used only to sense that the ASD relay is energized.
When energized, the ASD relay provides power to operate the injectors, ignition coil, generator field, O2 sensor heaters (both upstream and downstream), and also provides a sense circuit to the PCM for diagnostic purposes. The PCM energizes the ASD any time there is a Crankshaft Position sensor signal that exceeds a predetermined value. The ASD relay can also be energized after the engine has been turned off to perform an O2 sensor heater test, if vehicle is equipped with OBD II diagnostics.
With SBEC III, the ASD relay's electromagnet is fed battery voltage, not ignition voltage. The PCM still provides the ground. As mentioned earlier, the PCM energizes the ASD relay during an O2 sensor heater test. This test is performed only after the engine has been shut OFF. The PCM still operates internally to perform several checks, including monitoring the O2 sensor heaters. This and other DTC tests are explained in detail in the On-Board Diagnostic Student Reference Book.
BATTERY VOLTAGE - PCM INPUT
The direct battery feed to the PCM is used as a reference point to sense battery voltage.
In order for the PCM to operate, it must be supplied with battery voltage and ground. The PCM monitors the direct battery feed input to determine battery charging rate and to control the injector initial opening point. It also has back-up RAM memory used to store Diagnostic Trouble Codes (supply working DTC's). Direct battery feed is also used to perform key-OFF diagnostics and to supply working voltage to the controller for OBD II.
If battery voltage is low the PCM will increase injector pulse width (period of time that the injector is energized).
Effect on Fuel Injectors
Fuel injectors are rated for operation at a specific voltage. If the voltage increases, the plunger will open faster and conversely, if voltage is low the injector will be slow to open. Therefore, if sensed battery voltage drops, the PCM increases injector pulse-width to maintain the same volume of fuel through the injector.
Charging
The PCM uses sensed battery voltage to verify that target charging voltage (determined by Battery Temperature Sensor) is being reached. To maintain the target charging voltage, the PCM will full field the generator to 0.5 volt above target then turn OFF to 0.5 volt below target. This will continue to occur up to a 100 Hz frequency, 100 times per second.
ENGINE COOLANT TEMPERATURE SENSOR - PCM INPUT
Fig. 2 Engine Coolant Temperature Sensor:
The engine coolant temperature sensor threads into the front of the driver side cylinder head.
The PCM determines engine coolant temperature from the coolant temperature sensor. The ECT sensor is a two wire Negative Thermal Coefficient (NTC) sensor. The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases. As coolant temperature varies, the coolant temperature sensor resistance changes resulting in a different voltage value at the PCM engine coolant sense circuit.
Until the engine reaches operating temperature, the PCM demands slightly richer air-fuel mixtures and higher idle speeds.
This sensor is also used for cooling fan control and A/C cutoff at high coolant temperatures.
This 3-way sensor is also used for the water temperature gauge and dashboard warning light.
OXYGEN SENSOR (O2S SENSOR) - PCM INPUT
Fig. 3 Upstream Oxygen Sensors:
The upstream O2 sensors are in the exhaust manifolds.
Fig. 4 Right Rear Oxygen Sensor:
Fig. 5 Left Rear Oxygen Sensor:
The downstream O2 sensor are in the exhaust system near the rear axle or.
The O2 Sensors are zirconium dioxide, four wire and heated. The heater uses two of the sensors' four wires. One is common ground, the other provides battery voltage to the heater from the ASD Relay. One of the remaining wires is a sensor signal input to the PCM. The fourth wire is signal ground. The O2 Sensors deliver a voltage signal (0 - 1 volt) to the PCM inversely proportional to the amount of oxygen in the exhaust. If the oxygen content is low, the output voltage is high; if the oxygen content is high, the output voltage low. The O2 Sensors must have a source of oxygen from outside the exhaust stream for comparison. O2 Sensors receive their fresh oxygen supply through the wire harness. This is why it is important to never solder an O2 Sensor connector or pack the connector with grease.
The Automatic Shutdown (ASD) relay supplies battery voltage to both the upstream and downstream heated oxygen sensors. The oxygen sensors are equipped with a heating element. The heating elements reduce the time required for the sensors to reach operating temperature. The O2 Sensor uses a Positive Thermal Coefficient (PTC) heater element. As temperature increases, resistance increases. At ambient temperatures around 21 °C (70 °F), the resistance of the heating element is approximately 6 ohms for the Downstream Sensor and is approximately 4.5 ohms for the Upstream Sensor. As the sensor's temperature increases, resistance in the heater element increases.
Upstream Oxygen Sensor 1/1
The input from the upstream heated oxygen sensor tells the PCM the oxygen content of the exhaust gas. Based on this input, the PCM fine tunes the air-fuel ratio by adjusting injector pulse width. Separate controlled ground circuits are run through the PCM for the upstream O2 sensors.
The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air/fuel mixture), the sensor produces voltage as low as 0.1 volt. When there is a lesser amount of oxygen present (rich air/fuel mixture) the sensor produces a voltage as high as 1.0 volt. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch.
The oxygen sensors are equipped with a heating element that keeps the sensors at proper operating temperature during all operating modes. Heating the sensor allows the system to enter into closed loop operation sooner. Also, it allows the system to remain in closed loop operation during periods of extended idle.
In Closed Loop operation the PCM monitors the O2S input (along with other inputs) and adjusts the injector pulse width accordingly. During Open Loop operation the PCM ignores the O2 sensor input. The PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
Downstream Oxygen Sensor 1/2
The downstream heated oxygen sensor input is used to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, the PCM calculates catalytic convertor efficiency. If the oxygen leaving the catalyst is too lean (excess oxygen), the PCM increases the upstream O2 goal, which increases fuel in the mixture, causing less oxygen to be left over. Conversely, if the oxygen content leaving the catalyst is too rich (not enough oxygen) the PCM decreases the upstream O2 goal down which removes fuel from the mixture causing more oxygen to be left over. This function only occurs during downstream closed loop mode operation.
IGNITION SENSE - PCM INPUT
The ignition sense input informs the Powertrain Control Module (PCM) that the ignition switch is in the crank or run position.
INTAKE AIR TEMPERATURE SENSOR - PCM INPUT
Fig. 6 Intake Air Temperature Sensor:
The Intake Air Temperature Sensor threads into the air cleaner. The sensor measures air temperature.
The intake air temperature sensor input is one of the inputs the PCM monitors to determine the required injector pulse width.
MANIFOLD ABSOLUTE PRESSURE SENSOR - PCM INPUT
Fig. 7 MAP Sensor:
The MAP sensor mounts to the drivers side intake manifold plenum.
The MAP serves as a PCM input, using a silicon based sensing unit, to provide data on the manifold vacuum that draws the air/fuel mixture into the combustion chamber. The PCM requires this information to determine injector pulse width and spark advance. When MAP equals Barometric pressure, the pulse width will be at maximum.
Also like the cam and crank sensors, a 5 volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero pressure reading is 0 - 5 volts and full scale is 4.5 volts For a pressure swing of 0 - 15 psi the voltage changes 4.0 volts. The sensor is supplied a regulated 4.8 - 5.1 volts to operate the sensor. Like the cam and crank sensors ground is provided through the sensor return circuit.
The MAP sensor input is the number one contributor to pulse width. The most important function of the MAP sensor is to determine barometric pressure. The PCM needs to know if the vehicle is at sea level or is it in Denver at 5000 feet above sea level, because the air density changes with altitude. It will also help to correct for varying weather conditions. If a hurricane was coming through the pressure would be very, very low or there could be a real fair weather, high pressure area. This is important because as air pressure changes the barometric pressure changes. Barometric pressure and altitude have a direct inverse correlation, as altitude goes up barometric goes down. The first thing that happens as the key is rolled on, before reaching the crank position, the PCM powers up, comes around and looks at the MAP voltage, and based upon the voltage it sees, it knows the current barometric pressure relative to altitude. Once the engine starts, the PCM looks at the voltage again, continuously every 12 milliseconds, and compares the current voltage to what it was at key on. The difference between current and what it was at key on is manifold vacuum.
During key ON (engine not running) the sensor reads (updates) barometric pressure. A normal range can be obtained by monitoring known good sensor in you work area.
As the altitude increases the air becomes thinner (less oxygen). If a vehicle is started and driven to a very different altitude than where it was at key ON the barometric pressure needs to be updated. Any time the PCM sees Wide Open throttle, based upon TPS angle and RPM it will update barometric pressure in the MAP memory cell. With periodic updates, the PCM can make its calculations more effectively.
The PCM uses the MAP sensor to aid in calculating the following:
- Barometric pressure
- Engine load
- Manifold pressure
- Injector pulse-width
- Spark-advance programs
- Shift-point strategies (F4AC 1 transmissions only, via the CCD bus)
- Idle speed
- Decel fuel shutoff
The MAP sensor signal is provided from a single piezoresistive element located in the center of a diaphragm. The element and diaphragm are both made of silicone. As the pressures changes the diaphragm moves causing the element to deflect which stresses the silicone. When silicone is exposed to stress its resistance changes. As manifold vacuum increases, the MAP sensor input voltage decreases proportionally. The sensor also contains electronics that condition the signal and provide temperature compensation.
The PCM recognizes a decrease in manifold pressure by monitoring a decrease in voltage from the reading stored in the barometric pressure memory cell. The MAP sensor is a linear sensor; as pressure changes, voltage changes proportionately. The range of voltage output from the sensor is usually between 4.6 volts at sea level to as low as 0.3 volts at 26 in.Hg (Table 1). Barometric pressure is the pressure exerted by the atmosphere upon an object. At sea level on a standard day, no storm, barometric pressure is 29.92 in.Hg. For every 100 feet of altitude barometric pressure drops 0.10 in.Hg. If a storm goes through it can either add, high pressure, or decrease, low pressure, from what should be present for that altitude. You should make a habit of knowing what the average pressure and corresponding barometric pressure is for your area. Always use the Diagnostic Test Procedures for MAP sensor testing.
SENSOR RETURN - PCM INPUT
The sensor return circuit provides a low electrical noise ground reference for all of the systems sensors. The sensor return circuit connects to internal ground circuits within the Powertrain Control Module (PCM).
SCI RECEIVE - PCM INPUT
SCI Receive is the serial data communication receive circuit for the DRB scan tool. The Powertrain Control Module (PCM) receives data from the DRB through the SCI Receive circuit.
THROTTLE POSITION SENSOR - PCM INPUT
Fig. 8 Throttle Position Sensor:
The TPS is mounted on the drivers side throttle body. The sensor connects to the throttle blade shaft. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage).
The fuel injection system uses only one Throttle Position Sensor (TPS). The TPS is a variable resistor that provides the PCM with an input signal (voltage). The signal represents throttle blade position. As the position of the throttle blade changes, the resistance of the TPS changes.
The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents throttle blade position. The TPS output voltage to the PCM varies from approximately 0.5 volt at minimum throttle opening (idle) to 3.5 volts at wide open throttle. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. The PCM also adjusts fuel injector pulse width and ignition timing based on these inputs.
VEHICLE SPEED SENSOR - PCM INPUT
Fig. 9 Vehicle Speed Sensor, Skip Shift Solenoid And Reverse Lockout Solenoid:
The vehicle speed sensor is located on the drivers side of the transmission.
The Power Control Module (PCM) determines vehicle speed from the speed sensor input.
From the speed sensor input to the PCM determine the following:
- To prevent deceleration fuel cutoff at low vehicle speeds
- What gear the vehicle is operating in for 2-3 lockout
- Idle speed control delay time based on whether the vehicle is moving
- Cooling fan turns OFF at 77 mph, when accelerating, and turns back on at 67 mph.
AUTOMATIC SHUTDOWN RELAY - PCM OUTPUT
The ASD relay is located in the PDC with all the other relays. A decal on the inside of the PDC covers shows the locations of each relay and fuse contained in the PDC.
The Automatic Shutdown (ASD) relay supplies battery voltage to the fuel injectors, electronic ignition coil and the heating elements in the oxygen sensors.
The PCM controls the relay by switching the ground path for the solenoid side of the relay ON and OFF. The PCM turns the ground path OFF when the ignition switch is in the OFF position unless the O2 Heater Monitor test is being run. When the ignition switch is in the ON or Crank position, the PCM monitors the crankshaft position sensor and camshaft position sensor signals to determine engine speed and ignition timing (coil dwell). If the PCM does not receive the crankshaft position sensor and camshaft position sensor signals when the ignition switch is in the Run position, it will de-energize the ASD relay.
FUEL PUMP RELAY - PCM OUTPUT
The fuel pump relay is located in the PDC. A decal on the inside of the PDC covers shows the locations of each relay and fuse contained in the PDC.
The fuel pump relay supplies battery voltage to the fuel pump. A buss bar in the Power Distribution Center (PDC) supplies voltage to the solenoid side and contact side of the relay. The fuel pump relay power circuit contains a fuse between the buss bar in the PDC and the relay. The fuse also protects the power circuit for the Automatic Shutdown (ASD) relay. The fuse is located in the PDC. Refer to the Wiring Diagrams for circuit information.
The PCM controls the fuel pump relay by switching the ground path for the solenoid side of the relay ON and OFF. The PCM turns the ground path OFF when the ignition switch is in the OFF position. When the ignition switch is in the ON position, the PCM energizes the fuel pump. If the crankshaft position sensor does not detect engine rotation, the PCM de-energizes the relay after approximately one second.
EVAP PURGE SOLENOID - PCM OUTPUT
Fig. 10 EVAP Purge Solenoid:
The EVAP purge solenoid controls the vacuum source for the EVAP canister. The PCM regulates the EVAP purge solenoid.
The PCM operates the solenoid by switching the ground circuit ON and OFF based on engine operating conditions. When energized, the solenoid prevents vacuum from reaching the evaporative canister.
When not energized the solenoid allows vacuum to flow to the canister.
When the PCM grounds the solenoid, it energizes and vacuum does not operate the evaporative canister valve. The PCM removes the ground to the solenoid when the engine reaches a specified temperature and the time delay interval has occurred. When the solenoid de-energizes, vacuum flows to the canister purge valve. Vapors are purged from the canister and flow to the throttle body.
The purge solenoid also energizes during certain idle conditions to update the fuel delivery calibration.
Refer to the Evaporative Emissions for more information.
IDLE AIR CONTROL MOTOR - PCM OUTPUT
Fig. 11 Idle Air Control Motor:
The idle air control motor is mounted at the front right of the intake manifold.
The motor controls air flow through a passage connected to both intake manifold plenums. The PCM operates the idle air control motor. The PCM adjusts engine idle speed through the idle air control motor to compensate for engine load or ambient conditions.
The idle air control motor pintle protrudes into a housing connected to the idle air passage. The pintle controls air flow through the intake manifold while the engine idles. By extending or retracting the pintle, the PCM controls adjusts idle speed for different operating conditions.
The PCM adjusts the idle air control motor based on inputs it receives. The inputs affecting idle speed include throttle position, crankshaft position, engine coolant temperature, plus brake switch and air conditioning request signals. By increasing airflow when the throttle blade closes quickly at road speeds, the PCM prevents deceleration die out.
DATA LINK CONNECTOR - PCM OUTPUT
The data link connector is located inside the vehicle, below instrument panel to the left of the clutch pedal.
Fig. 12 Data Link Connector:
The data link connector (diagnostic connector) links the DRB scan tool with the PCM. Refer to On-Board Diagnostics in Emission .
MALFUNCTION INDICATOR (CHECK ENGINE) LAMP - PCM OUTPUT
Refer to the Instrument Panel Systems for more information.
The PCM supplies the malfunction indicator (check engine) lamp ON/OFF signal to the instrument panel through the CCD Bus. The CCD Bus is a communications port. Various modules use the CCD Bus to exchange information.
The Check Engine lamp comes on each time the ignition key is turned ON and stays ON for 3 seconds as a bulb test.
The Malfunction Indicator Lamp (MIL) stays ON continuously, when the PCM has entered a Limp-In mode or identified a failed emission component. During Limp-in Mode, the PCM attempts to keep the system operational. The MIL signals the need for immediate service. In limp-in mode, the PCM compensates for the failure of certain components that send incorrect signals. The PCM substitutes for the incorrect signals with inputs from other sensors.
If the PCM detects active engine misfire severe enough to cause catalyst damage, it flashes the MIL. At the same time the PCM also sets a Diagnostic Trouble Code (DTC).
For signals that can trigger the MIL (Check Engine Lamp) refer to the On-Board Diagnostics Chart.
RADIATOR FAN ON RELAY - PCM OUTPUT
The relay is located in the PDC. The inside top of the PDC cover has label showing relay and fuse identification.
The radiator fan ON relay energizes when the PCM provides a ground to the relay. The radiator fan relay is located below the heater blower motor housing. The PCM grounds the radiator fan relay when engine coolant exceeds 97 °C (207 °F). The PCM turns the fan off when coolant temperature drops to 94 °C (201 °F). Also, the PCM energizes the ON relay whenever the A/C system operates. Refer to Radiator Fan LOW/HIGH Relay for fan operation.
RADIATOR FAN LOW/HIGH RELAY - PCM OUTPUT
The relay is located in the PDC. The inside top of the PDC cover has label showing relay and fuse identification.
The radiator fan LOW/HIGH relay works in conjunction with the radiator fan ON relay. If the coolant temperature is below 102 °C (216 °F) the current flow for the fan is through the normally closed contacts of the LOW/HIGH relay. If the coolant temperature is above 102 °C (216 °F) LOW/HIGH relay and the radiator fan changes to high speed. The PCM turns OFF high speed fan operation when coolant temperature drops to 102 °C (216 °F). The low speed will continue until temperature drops below 94 °C (201 °F).. Cooling fan turns OFF at 77 mph, when accelerating, and turns back ON at 67 mph.
REVERSE LOCKOUT SOLENOID - PCM OUTPUT
Fig. 9 Vehicle Speed Sensor, Skip Shift Solenoid And Reverse Lockout Solenoid:
The reverse lockout solenoid prevents the operator from shifting into reverse when the vehicle is speed is greater than 5 mph. When vehicle speed is less than 5 mph the PCM provides a ground for the solenoid (energized) and allows shifting. When vehicle speed is greater than 5 mph the solenoid is deactivated and prevents the transmission from being shifted into reverse.
FIRST TO FOURTH GEAR SHIFT INDICATOR LAMP - PCM OUTPUT
The PCM operates the first gear to fourth gear shift lamp. The lamp informs the driver to shift into fourth gear on the next transmission upshift. The PCM illuminates the shift lamp when the following conditions have been met:
- Vehicle speed between 12 and 18 mph
- Transmission in first gear
- Engine speed greater than 608 rpm
- Throttle position less than 23 percent (less than 0.68 volts over closed throttle TPS voltage)
- Coolant temperature above 41 °C (106 °F)
SKIP SHIFT SOLENOID - PCM OUTPUT
Fig. 13 Disconnecting Throttle Cable:
The skip shift solenoid prevents the operator from shifting into second or third gear during certain conditions. The PCM controls the skip shift solenoid. The PCM locks out second and third gear when all of the following conditions are met:
- Engine coolant exceeds 41 °C (106 °F)
- Vehicle speed is between 12 and 18 mph
- Engine operating above 608 rpm
- The PCM verified first gear speed/RPM
- Throttle position sensor (TPS) signal is less than 0.068 volt above closed throttle (23 percent throttle opening)
The solenoid resets when vehicle speed drops below 2 mph.
SCI TRANSMIT - PCM INPUT
SCI Transmit is the serial data communication transmit circuit to the DRB scan tool. The Power- train Control Module (PCM) transmit data to the DRB through the SCI transmit circuit.
TACHOMETER - PCM OUTPUT
The PCM operates the tachometer on the instrument panel. The PCM calculates engine RPM from the crankshaft position sensor input.