PCM Outputs

Service Engine Soon (Malfunction Indicator Lamp Telltale)
The malfunction indicator lamp (MIL) (previously called "SERVICE ENGINE SOON") is used by the PCM to signal the operator of the vehicle of a possible problem.

When the PCM requires the indicator lamp to be turned on, it will supply a ground signal for the lamp. If the microprocessor is disabled for any reason, a ground for the check engine indicator lamp will be automatically provided.

Fan Control Relay
The fan control relay is used by the PCM to control engine cooling fan operation. When the PCM supplies a ground to the coil of the fan control relay, current is allowed to flow through the switch contacts of the relay to the engine cooling fan.

The engine cooling fan will be turned on or off by the PCM dependent upon engine coolant temperature, vehicle speed or A/C On request. Under high ambient conditions, the fan may run up to four minutes with the key off. If the PCM should become disabled a ground for the fan control relay will be automatically provided.

A/C Clutch Control Relay
The A/C clutch control relay is used by the PCM to turn on or off the A/C compressor clutch coil. When the PCM receives an A/C request signal, it will supply a ground to the A/C clutch control relay, energizing the relay and allowing the A/C compressor clutch coil to be energized. This allows the A/C compressor to be turned On. During certain driving conditions, the PCM will turn off the A/C compressor by removing the ground for the A/C clutch control relay.

Upshift

Upshift Indicator (manual Transmission Only):

The upshift telltale is used, on vehicles equipped with a manual transaxle, to signal the driver to upshift. Shifting each time the upshift light comes on will obtain maximum fuel economy.

To turn on the indicator lamp, the PCM will supply a ground allowing current to flow through the lamp, turning it on.

Hot Telltale

Hot Telltale Indicator:

The hot telltale is used by the PCM to indicate to the operator of the vehicle a possible engine overheat condition. If the PCM determines from signals received from the coolant temperature sensor that the engine is running too hot, it will turn on the coolant temperature telltale lamp by supplying a ground. The hot telltale lamp is also used when there is a transaxle overheat condition.

Electrical Variable Orifice (EVO) Solenoid
The PCM will supply battery voltage and a ground for the electrical variable orifice (EVO) solenoid. The PCM controls both the high side (voltage input) and low side (ground control) to the solenoid so that current control is retained in the presence of any output fault condition.



Idle Air Control System
The PCM controls engine idle speed by controlling current to two stepper coils contained within the idle air control valve assembly.

By controlling current to both of the coils, the PCM can control engine idle speed by allowing air to bypass around the throttle plate.

EVAP Cannister Purge Control Solenoid
The EVAP canister purge solenoid is used by the PCM to control fuel vapor flow from the EVAP carbon canister to the intake manifold where it is burned in the combustion process during engine operation. This helps reduce the amount of hydrocarbons (HC) emissions emitted into the atmosphere. The PCM will supply a ground to the solenoid opening it and allowing fuel vapors to flow from the canister to the intake manifold. When the ground is removed the solenoid will close.


Fuel Pump Relay
The PCM will supply power to the fuel pump relay controlling operation of the in-tank electric fuel pump. The PCM will energize the relay when the ignition is first turned to the Run position. If the vehicle is not started within two seconds the relay will be de-energized until reference pulses, indicating the engine is running, are received from the ignition module. The fuel pump relay will be de-energized, turning off the fuel pump, when the ignition is turned to Off or if the ignition is in Run and no engine reference pulses are seen within 2 (+or- 0.75) seconds.

Electronic Ignition (EI) Interface
The PCM supplies two signals to the electronic ignition module. One signal is an ignition timing waveform, and the other signal is a fail-safe discrete signal that informs the ignition module that the PCM is operational. The falling edge of the timing waveform indicates the beginning of the spark event. The timing waveform is a 0 to 5 volt variable duty-cycle, and frequency, based on the engine waveform and is generated by the PCM to indicate spark advance.

The discrete signal is a constant five volts while the PCM is operational and grounded when the PCM is not operational.

Fuel Control
In the multi-port system, four injectors are used. These four injectors supply fuel to each cylinder when the PCM provides a ground.

If the PCM should become non-operational, the PCM will deliver a set amount of fuel, based on inputs received from the manifold absolute pressure (MAP) sensor and engine coolant temperature (ECT) sensor.


Injector Pulse Output
The PCM supplies an output to the instrument cluster (speedometer/odometer), the passive restraint module and the cruise control module (if applicable). This signal is 5000 pulses/mile, representing the divided down vehicle speed. It is a square wave signal from 0 to 12 volts.

Serial Data
On vehicles equipped with an automatic trans axle the powertrain control module (PCM) will have an internal serial data line. This line will allow the engine controller (EC) to send and receive signals from the transaxle controller (TC) and ABS. The EC will control this serial data line within the PCM.