Part 2 of 2
KNOCK SENSOR - PCM INPUTKnock Sensor:
The knock sensor threads into the side of the cylinder block. The knock sensor is designed to detect engine vibration that is caused by detonation.
When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.
Knock sensors contain a piezoelectric material which sends an input voltage (signal) to the PCM. As the intensity of the engine knock vibration increases, the knock sensor output voltage also increases.
The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives as an input the knock sensor voltage signal. If the signal rises above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard.
The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed.
Knock retard uses its own short term and long term memory program.
Long term memory stores previous detonation information in its battery-backed RAM. The maximum authority that long term memory has over timing retard can be calibrated.
Short term memory is allowed to retard timing up to a preset amount under all operating conditions (as long as rpm is above the minimum rpm) except WOT. The PCM, using short term memory, can respond quickly to retard timing when engine knock is detected. Short term memory is lost any time the ignition key is turned off.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR - PCM INPUT
Manifold Absolute Pressure Sensor:
The MAP sensor mounts to the intake manifold.
The PCM supplies 5 volts direct current to the MAP sensor. The MAP sensor converts intake manifold pressure into voltage. The PCM monitors the MAP sensor output voltage. As vacuum increases MAP sensor voltage decreases proportionately. Also. as vacuum decreases, MAP sensor voltage increase proportionately.
At key on, before the engine is started, the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the PCM determines intake manifold pressure from the MAP sensor voltage. Based on MAP sensor voltage and inputs from other sensors, the PCM adjusts spark advance and the air/fuel mixture.
If the PCM considers the MAP Sensor information inaccurate, the PCM moves into "limp-in" mode. When the MAP Sensor is in limp-in, the PCM limits the engine speed as a function of the Throttle Position Sensor (TPS) to between 1500 and 4000 rpm. If the MAP Sensor sends realistic signals once again, the PCM moves out of limp-in and resumes using the MAP values.
During limp-in a DTC is set and the MIL illuminates.
POWER STEERING PRESSURE SWITCH - PCM INPUT
A pressure sensing switch is located on the power steering gear.
Power Steering Pressure Switch:
The switch provides an input to the PCM during periods of high pump load and low engine rpm, such as during parking maneuvers.
When power steering pump pressure exceeds 2758 kPa (400 psi), the switch is open. The PCM increases idle air flow through the IAC motor to prevent engine stalling. The PCM sends 12 volts through a resister to the sensor circuit to ground. 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).
SPEED CONTROL - PCM INPUT
The speed control system provides five separate voltages (inputs) to the Powertrain Control Module (PCM). The voltages correspond to the ON, OFF, SET, RESUME, CANCEL, and COAST.
The speed control ON voltage informs the PCM that the speed control system has been activated. The speed control SET voltage informs the PCM that a fixed vehicle speed has been selected. The speed control RESUME voltage indicates the previous fixed speed is requested. The speed control CANCEL voltage tells the PCM to deactivate but retain set speed in memory (same as depressing the brake pedal). The speed control OFF voltage tells the PCM that the speed control system has deactivated.
Inputs Required for Operation
The inputs required by the PCM to operate the Speed Control System include:
- Speed Control switches
- Brake switch
- Park/Neutral switch
- Vehicle speed signal
- Engine speed
- CCD bussed message from TCM
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.
PARK/NEUTRAL POSITION SWITCH - PCM INPUT
Park/Neutral Switch:
The park/neutral position switch is located on the automatic transaxle housing.
Manual transaxles do not use park/neutral switches. The switch provides an input to the PCM to indicate whether the automatic transaxle is in Park/Neutral, or a drive gear selection. This input is used to determine idle speed (varying with gear selection) and ignition timing advance. The park/neutral input is also used to cancel vehicle speed control. The park/neutral switch is sometimes referred to as the neutral safety switch.
The PCM delivers 8.5 volts to the center terminal of the Park/Neutral switch. When the gear shift lever is moved to either the Park or the Neutral position, the PCM receives a ground signal from the Park/Neutral switch. With the shift lever positioned in Drive or Reverse, the Park/Neutral switch contacts open, causing the signal to the PCM to go high.
THROTTLE POSITION SENSOR - PCM INPUT
Throttle Position Sensor And Idle Air Control Motor:
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 powertrain control module) represents throttle blade position. The TPS output voltage to the PCM varies from approximately 0.35 to 1.03 volts at minimum throttle opening (idle) to a maximum of 3.1 to 4.0 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.
When the TPS indicates a voltage that is too high, too low or not believable, the PCM sets a DTC. When the DTC is set, the MIL is illuminated and the PCM moves into limp-in mode. Limp-in for the TPS is divided into three categories:
- Idle
- Part-throttle
- Wide open throttle (WOT)
VEHICLE SPEED SIGNAL (VSS) - PCM INPUT
The PCM requires the VSS to be able to control the following programs:
- Speed Control
- IAC motor (during deceleration)
- Injection pulse width (during deceleration)
- OBD II diagnostics
- PCM mileage EEPROM
- Road speed shutdown
- Speedometer/Odometer (bused message)
NOTE: Road Speed Shutdown is the PCM shutting oft fuel injectors above a preset vehicle speed.
Vehicle Speed Sensor - Automatic Transmission:
Vehicle Speed Sensor - Manual Transmission:
The vehicle speed sensor is located in the transmission extension housing.
The vehicle speed sensor on 3 speed automatic and manual transaxle vehicles is a Hall-effect sensor. This sensor is mechanically driven by a pinion gear that is in mesh with the right axle drive shaft. The hall-effect sensor switches a 5 volt signal sent from the PCM from a ground to an open circuit.
Like all Hall-effect sensors, the electronics of the sensor needs a power source. This power source is provided by the PCM. It is the same 8 volt power supply that is used by the CKP and CMP sensors.
The vehicle speed sensor generates 8 pulses per sensor revolution. This signal, in conjunction with a closed throttle signal from the throttle position sensor, indicates 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.
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.
AIR CONDITIONING CLUTCH RELAY - PCM OUTPUT
The air conditioning clutch relay is located in the PDC. The inside top of the PDC cover has a label showing relay and fuse location.
The PCM controls the air conditioning clutch relay ground circuit. The A/C clutch relay coil side contains a 10 amp fuse between the buss bar in the Power Distribution Center (PDC) and the relay. The power side of this relay is fused with a 40 amp fuse. When the PCM receives an air conditioning input, it grounds the A/C compressor clutch relay and the radiator fan relay.
When the PCM senses low idle speeds or wide open throttle through the throttle position sensor, it removes the ground for the A/C compressor clutch relay. When the relay de-energizes, the contacts open preventing air conditioning clutch engagement. Also, if the PCM senses a part throttle launch condition, it disables the A/C compressor clutch for several seconds.
AUTOMATIC SHUTDOWN RELAY - PCM OUTPUT
The ASD relay is located in the PDC. The inside top of the PDC cover has a label showing relay and fuse location.
The Automatic Shutdown (ASD) relay supplies battery voltage to the fuel injectors, electronic ignition coil and the heating elements in the oxygen sensors generator field and PCM sense circuit.
A buss bar in the power distribution center (PDC) - supplies voltage to the solenoid side and contact side of the relay. The ASD 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 fuel pump relay and pump. The fuse is located in the PDC.
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.
CHARGING SYSTEM INDICATOR LAMP - PCM OUTPUT
The PCM turns the instrument panel Charging System Lamp on. Refer to the Charging system.
FUEL PUMP RELAY - PCM OUTPUT
The fuel pump relay is located in the PDC. The inside top of the PDC cover has a label showing relay and fuse location.
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.
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.
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.
Proportional Purge Solenoid:
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.
GENERATOR FIELD - PCM OUTPUT
Refer to the Battery for information and refer to the Charging. The PCM regulates the charging system voltage within a range of 12.9 - 15.0 volts. The charging system is turned ON and OFF with the Ignition Switch. When the Ignition Switch is turned to the ON position, battery voltage is applied to the generator rotor through one of the two field terminals to produce a magnetic field. The amount of DC current produced by the generator is controlled by the Electronic Voltage Regulator (EVR) in the PCM. This circuitry is connected in series with the second rotor field terminal and ground.
The voltage determined by the PCM as the final goal for the charging system is called "target charging voltage." The PCM monitors battery voltage. If the sensed voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage.
IDLE AIR CONTROL MOTOR - PCM OUTPUT
Idle Air Control Motor - Typical:
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
DATA LINK CONNECTOR - PCM OUTPUT
Data Link Connector:
The data link connector is located inside the vehicle, under the instrument panel, left of the steering column.
The data link connector (diagnostic connector) links the DRB scan tool with the powertrain control module (PCM). Refer to On-Board Diagnostics in the General Diagnosis.
FUEL INJECTORS - PCM OUTPUT
Fuel Injector:
The 2.0L engine uses electrically operated top feed fuel injectors. The Automatic Shutdown (ASD) relay supplies battery voltage to the fuel injectors. The PCM controls the ground path for each injector in sequence. By switching the ground paths on and off; the PCM fine-tunes injector pulse width, injector pulse width refers to the amount of time an injector operates.
The PCM determines injector synchronization from the camshaft position sensor and crankshaft position sensor inputs. The PCM grounds the ASD and fuel pump relays after receiving the camshaft position sensor and crankshaft position sensor inputs.
The PCM energizes the injectors in a sequential order during all engine operating conditions except start-up. For the first injector pulse width during start-up, all injectors are energized at the same time. Once the PCM determines crankshaft position, it begins energizing the injectors in sequence.
IGNITION COIL - PCM OUTPUT
Ignition Coil Pack:
The coil assembly consists of 2 coils molded together. The coil assembly is mounted over the valve cover.
High tension leads route to each cylinder from the coil. The coil fires two spark plugs every power-stroke. One plug is the cylinder under compression, the other cylinder fires on the exhaust stroke. Coil number one fires cylinders 1 and 4. Coil number two fires cylinders 2 and 3. The PCM determines which of the coils to charge and fire at the correct time.
The Auto Shutdown (ASD) relay provides battery voltage to the ignition coil. The PCM provides a ground contact (circuit) for energizing the coil. When the PCM breaks the contact, the energy in the coil primary transfers to the secondary causing the spark. The PCM will de-energize the ASD relay if it does not receive the crankshaft position sensor and camshaft position sensor inputs. Refer to Auto Shutdown (ASD) Relay-PCM Output for relay operation.
Base timing is non-adjustable, but is set from the factory at approximately 10 BTDC when the engine is warm and idling.
There is an adaptive dwell strategy that runs dwell from 4 to 6 msec when rpm is below 3,000 and battery voltage is 12-14 volts. During cranking, dwell can be as much as 200 msec. The adaptive dwell is driven by the sensed current flow through the injector drivers. Current flow is limited to 8 amps.
The low resistance of the primary coils can allow current flow in excess of 15 amps. The PCM has a current sensing device in the coil output circuit. As dwell time starts, the PCM allows current to flow. When the sensing device registers 8 amps, the PCM begins to regulate current flow to maintain and not exceed 8 amps through the remainder of the dwell time. This prevents the PCM from being damaged by excess current flow.
MALFUNCTION INDICATOR (CHECK ENGINE) LAMP - PCM OUTPUT
The PCM supplies the malfunction indicator (check engine) lamp on/off signal to the instrument panel through the PCI Bus. The P01 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.
SPEED CONTROL - PCM INPUT
The speed control system provides five separate voltages (inputs) to the Powertrain Control Module (PCM). The voltages correspond to the ON, OFF, SET, RESUME, CANCEL, and COAST.
The speed control ON voltage informs the PCM that the speed control system has been activated. The speed control SET voltage informs the PCM that a fixed vehicle speed has been selected, The speed control RESUME voltage indicates the previous fixed speed is requested. The speed control CANCEL voltage tells the PCM to deactivate but retain set speed in memory (same as depressing the brake pedal). The speed control COAST voltage informs the PCM to coast down to a new desired speed. The speed control OFF voltage tells the PCM that the speed control system has deactivated. Refer to the Speed Control for more speed control information.
SCI RECEIVE - PCM OUTPUT
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.
TACHOMETER - PCM OUTPUT
The PCM operates the tachometer on the instrument panel. The PCM calculates engine RPM from the crankshaft position sensor input. Sends the information to the cluster across the bus.
TORQUE CONVERTOR CLUTCH SOLENOID - PCM OUTPUT
Torque Convertor Clutch Solenoid:
Three-speed automatic transaxies use a torque converter clutch solenoid. The PCM controls the engagement of the torque converter clutch through the solenoid. The torque converter clutch is engaged up only in direct drive mode. Refer to the Transmission for information.