Other Control Outputs
OTHER OUTPUT SIGNALSOverview
The ECM also supplies other components in the car with signals and information computed with the aid of the sensor signals, These are:
^ Transmission Control Module (TCM)
^ Combined Instrument Panel
^ Trip computer
^ A/C compressor via A/C relay
Transmission Control Module
The TOM (1) receives the following information from the ECM (2):
^ Engine load signal from Mass Air Flow (MAF) Sensor (3)
^ Throttle opening from Throttle Position (TP) Potentiometer (4)
The information is used by the TCM to determine when a gear-change is required.
Combined Instrument Panel
Tachometer
The ECM (1) computes engine speed with the aid of the signal from the Engine Speed (RPM) Sensor (2). The RPM signal, which is used for engine management purposes, is also converted into a signal sent to the tachometer in the combined instrument (3), to inform the driver of the engine speed.
Temperature Gauge
The ECM computes the engine coolant temperature with the aid of the signal from the Engine Coolant Temperature (ECT) Sensor (4). The signal, which is used for engine management purposes, is also transmitted to the temperature gauge in the combined instrument.
Malfunction Indicator Lamp
The Malfunction Indicator Lamp (MIL) is operated by the ECM, while the TCM may also request its operation.
As a bulb-check function, the MIL lights up when the ignition is switched ON, and goes out when the engine STARTS.
he lamp also lights up if the ECM detects a fault which affects exhaust emissions, but will go out if the ECM determines that the fault is no longer present.
Trip Computer
The ECM supplies the trip computer with information regarding the quantity of fuel injected.
Among other purposes, the signal is used to indicate the fuel consumption.
A/C System
The A/C relay (2/22) is activated if the A/C switch is operated while the blower is running and system operation is enabled by the ECM. Power is then supplied to the A/C compressor electromagnetic clutch (8/3) and cycling of the compressor is controlled in the normal manner by the pressostat (7/53).
The compressor is switched out under the following conditions to prevent it running when full engine output is required or there is a risk of overheating:
^ The ECM switches out the unit for a maximum of 15 seconds (and a minimum of 3 seconds) at full acceleration, when the throttle is at WOT.
^ Risk of overheating: Operation of the A/C compressor is inhibited to reduce the load on the engine and to prevent a further rise in temperature if the engine coolant temperature is above 125°C (257°F)
^ If the system pressure exceeds approx. 3000 kPa (435 psi).
The ECM also inhibits compressor operation on starting to permit running conditions to stabilize. Starting of the compressor is delayed by approx. 5 to 15 seconds.