Part 2 of 2
Inlet/Intake Air TemperatureThe inlet air temperature sensor replaces the intake air temperature sensor and the battery temperature sensor. The PCM uses the information from the inlet air temperature sensor to determine values to use as an intake air temperature sensor and a battery temperature sensor.
The Intake Air Temperature (IAT) sensor value is used by the PCM to determine air density.
The PCM uses this information to calculate:
- Injector pulse width
- Adjustment of ignition timing (to prevent spark knock at high intake air temperatures)
Battery Temperature
The inlet air temperature sensor replaces the intake air temperature sensor and the battery temperature sensor. The PCM uses the information from the inlet air temperature sensor to determine values for the PCM to use as an intake air temperature sensor and a battery temperature sensor.
The battery temperature information along with data from monitored line voltage (B+), is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.
The battery temperature information is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled depending upon the battery temperature sensor input (example: disable purge, enable LDP). Most OBD II monitors are disabled below 20 °F.
Fig.6 MAP Sensor:
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR-PCM INPUT
The MAP sensor mounts to the intake manifold.
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 0.5V and full scale is 4.5V. For a pressure swing of 0 - 15 psi the voltage changes 4.0V. The sensor is supplied a regulated 4.8 to 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 (F4AC1 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. of 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 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.
Fig.7 Power Steering Pressure Switch:
POWER STEERING PRESSURE SWITCH-PCM INPUT
A pressure sensing switch is located on the power steering gear.
The switch provides an input to the PCM during periods of high pump load and low engine RPM; such as during parking maneuvers. The PCM sends 12 volts through a resistor to the sensor circuit to ground.
When power steering pump pressure exceeds 4137 kPa (600 psi), the switch is open. The PCM increases idle air flow through the IAC motor to prevent engine stalling. When pump pressure is low, the switch is closed.
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.
Fig.8 Throttle Position Sensor:
THROTTLE POSITION SENSOR-PCM INPUT
The throttle position sensor mounts to the side of the throttle body.
The Throttle Position Sensor (TPS) connects to the throttle blade shaft. 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 DC 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 a maximum of 3.7 volts at wide open throttle.
Along with inputs from other sensors, the PCM uses 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 SIGNAL-PCM INPUT
Fig.9 Vehicle Speed Sensor-Manual Transmission:
The vehicle speed sensor is located in the transmission extension housing.
Fig.10 Output Speed Sensor-Automatic Transaxle:
Automatic
The transaxle control module (TCM) supplies the vehicle speed signal to the PCM based on the output shaft speed. The PCM sends a 5 volt signal to the TCM. The TCM switches this signal to a ground, and then opens the circuit at a rate of 8000 pulses per mile. When the PCM counts 8000 pulses, the PCM assumes the vehicle has traveled one mile. The output speed sensor is located on the side of the transaxle.
The speed and distance signals, along with a closed throttle signal from the TPS, determine if a closed throttle deceleration or normal idle condition (vehicle stopped) exists. Under deceleration conditions, the PCM adjusts the idle air control motor to maintain a desired MAP value. Under idle conditions, the PCM adjusts the idle air control motor to maintain a desired engine speed.
Manual
The sensor input is used by the PCM to determine vehicle speed and distance traveled and is a Hall-effect sensor.
The Hall-effect sensor generates 8 pulses per sensor revolution. These signals, in conjunction with a closed throttle signal from the throttle position sensor, indicate a closed throttle deceleration to the PCM. Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value.
Like all Hall-effect sensors, the electronics of the sensor needs a power source. This power source is provided by the PCM. The sensor switches a 5 volt signal sent from the PCM from a ground to an open circuit. It is the same 9 volt power supply that is used by the CKP and CMP sensors.
When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received). Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed.
The vehicle speed sensor signal is also used to operate the following functions or systems:
- Speedometer
- Speed control
- Daytime Running Lights (Canadian Vehicles only).
The VSS used on 3 speed automatic and manual transaxle vehicles This sensor is mechanically driven by a pinion gear that is in mesh with the right axle drive shaft. When the PCM counts 4000 pulses, the PCM assumes the vehicle has traveled one mile.
Fig.11 Power Distribution Center(PDC):
AUTOMATIC SHUTDOWN RELAY-PCM OUTPUT
The ASD relay and fuel pump relay are located in the Power Distribution Center (PDC) near the Air Cleaner. The inside top of the PDC cover has a label showing relay and fuse location. They are ISO relays.
The PCM operates the Automatic Shut Down (ASD) relay and fuel pump relay. The PCM operates them by switching the ground path for the relays on and off.
The ASD relay connects battery voltage to the fuel injectors, ignition coil, generator field, and the heating elements in the oxygen sensors. The fuel pump relay connects battery voltage to the fuel pump.
The PCM turns the ground path off when the ignition switch is in the Off position. Both relays are off. 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. If the PCM does not receive a crankshaft position sensor signal and camshaft position sensor signal when the ignition switch is in the Run position, it de-energizes both relays. When the relays are de-energized, battery voltage is not supplied to the fuel injectors, ignition coil, generator field, and the heating elements in the oxygen sensors, and fuel pump.
Fig.12 Proportional Purge Solenoid:
PROPORTIONAL PURGE SOLENOID-PCM OUTPUT
All vehicles use a proportional purge solenoid. The solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The PCM operates the solenoid.
All vehicles use a proportional purge solenoid. The solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The PCM operates the solenoid.
During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged.
The proportional purge solenoid operates at a frequency of 200 hz and is controlled by an engine controller circuit that senses the current being applied to the proportional purge solenoid and then adjusts that current to achieve the desired purge flow. The proportional purge solenoid controls the purge rate of fuel vapors from the vapor canister and fuel tank to the engine intake manifold.
Fig.13 Idle Air Control Motor:
IDLE AIR CONTROL MOTOR-PCM OUTPUT
The Idle Air Control (IAC) motor is mounted on the throttle body. 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, coolant temperature or barometric pressure changes.
The throttle body has an air bypass passage that provides air for the engine during closed throttle idle. The idle air control motor pintle protrudes into the air bypass passage and regulates air flow through it.
The PCM adjusts engine idle speed by moving the IAC motor pintle in and out of the bypass passage. The adjustments are based on inputs the PCM receives. The inputs are from the throttle position sensor, crankshaft position sensor, coolant temperature sensor, MAP sensor, vehicle speed sensor and various switch operations (brake, park/neutral, air conditioning).
When engine rpm is above idle speed, the IAC is used for the following functions:
- Off-idle dashpot
- Deceleration air flow control
- A/C compressor load control (also opens the passage slightly before the compressor is engaged so that the engine rpm does not dip down when the compressor engages)
Target Idle
Target idle is determined by the following inputs:
- Gear position
- ECT Sensor
- Battery voltage
- Ambient/Battery Temperature Sensor
- VSS
- TPS
- MAP Sensor
Fig.14 Data Link Connector:
DATA LINK CONNECTOR
The data link connector is located inside the vehicle, under the instrument panel, at the driver's kick panel.
The data link connector (diagnostic connector) links the DRB scan tool with the Powertrain Control Module (PCM). Refer to On-Board Diagnostics.
MALFUNCTION INDICATOR (CHECK ENGINE) LAMP-PCM OUTPUT
Refer to the Instrument Panel Systems for more information.
The PCM supplies the malfunction indicator (check engine) Tamp on/off signal to the instrument panel through the PCI Bus. The PCI Bus is a communications port. Various modules use the PCI 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.
SCI TRANSMIT-PCM INPUT
SCI Transmit is the serial data communication transmit circuit to the DRB scan tool. The Powertrain Control Module (PCM) transmit data to the DRB through the SCI transmit circuit.
RADIATOR FAN RELAYS-PCM OUTPUT
The radiator fan relays are located in the PDC. The inside top of the PDC cover has a label showing relay and fuse location.
The PCM energizes the radiator fans through either the low or high speed radiator fan relay. The PCM controls the ground circuit for the coil side of the relay. Power for both relay coils is supplied through a 10 amp fuse in the PDC. Power for both relay contacts is supplied power through a 40 amp fuse in the PDC. Refer to the Wiring Diagrams for circuit information.
The PCM monitors the A/C compressor discharge (high side) pressure through the air conditioning pressure transducer. Depending on engine coolant temperature and A/C system high side pressure, both fans operate at either low or high speed.
TACHOMETER-PCM OUTPUT
Refer to the Instrument panel System for more information.
The tachometer receives its information across the PCI Bus from the Body Control Module (BCM). Information on engine RPM is transmitted from the Powertrain Control Module (PCM) across the PCI Bus to the BCM. The BCM calculates the position of the tachometer pointer based on the input from the PCM and adjusts the position of the gauge pointer to the necessary position. This signal is sent over the PCI Bus to the instrument cluster.
THROTTLE BODY
The throttle body mounts to the intake manifold. The throttle position sensor and idle air control motor attach to the throttle body.
At above idle conditions, air flow through the throttle body is controlled by a cable operated throttle blade. During closed throttle idle conditions, the idle air control motor control air flow.