Other functions controlled by control modules: Notes

Other functions can be controlled by the control modules 

On certain systems the engine control module (ECM) is also used to control functions other than fuel, ignition and idle air trim. Because the control module already knows the engine drive relationship it is just a question of connecting components and programming the control module.

The control module is often connected to other control systems in order to send information to them. The following can occur.

Air conditioning (AC) 

The air conditioning (A/C) compressor is controlled via a relay (29). The control module can disconnect the compressor at:

• Wide open throttle (WOT) for the maximum acceleration, using the signals from the throttle position (TP) sensor signal.
• Hot engine where there is a risk of overheating, using signals from the engine coolant temperature (ECT) sensor.
• Excessive pressure in the air conditioning (A/C) system, using signals from the high pressure sensor (16) in the AC system.

Engine cooling fan (FC) 

Controlled via a relay (24).

The control module can start the engine cooling fan (FC) if

• Engine coolant temperature (ECT) rises above a certain value, based on information from the engine coolant temperature (ECT) sensor.
• AC is selected when the vehicle speed is low, based on information from the speedometer and climate control system.
• Excessive pressure in the air conditioning (A/C) system, based on information from the pressure sensor in the AC system.
• The exhaust temperature is too high. The control module can derive exhaust temperature theoretically based on information about engine speed (RPM), load and throttle position.

If the engine has been under heavy load the engine cooling fan (FC) will occasionally continue running for one or more minutes after the engine has been switched off. This is called engine cooling fan (FC) "run-on". The control module calculates whether the engine cooling fan (FC) should run on by looking at how the engine is loaded and how high the engine coolant temperature (ECT) is.

Evaporative system for fuel vapor 

Normally called the EVAP system which stands for "Evaporative Emission System".

The evaporative emission (EVAP) system takes care of fuel vapor in the fuel tank so that it is not released into the atmosphere. The fuel which evaporates is drawn to and stored in a reservoir with a carbon filter which is called a canister. While driving the canister is drained using an electrical canister purge (CP) valve (26).

The control module determines when the canister purge (CP) valve is opened. When the valve is opened the fuel vapor is routed to the intake manifold and is mixed with the air flowing into the engine.

The control module determines when the canister purge (CP) valve is opened. When the valve is opened the fuel vapor is routed to the intake manifold and is mixed with the air flowing into the engine.

Exhaust gas recirculation 

Normally called the EGR system which stands for "Exhaust Gas Recirculation".

Exhaust gas recirculation is used to minimize the amount of nitrous oxides (NO_x ) left in the exhaust gases. nitrous oxides are a compound of the oxygen and the nitrogen in the air which develop at high pressures and temperatures. By routing a part of the exhaust gases to the engine via an Exhaust Gas Recirculation Valve (EGR Valve) the combustion temperature is lowered. This is partially because exhaust gases contain a relatively high amount of water vapor which requires a lot of energy to heat up and partially because the exhaust gases are inert and take up room but do participate in the combustion process.

The control module controls the EGR valve opening via a solenoid valve/vacuum converter (27).

The solenoid valve opens only when the engine is at operating temperature at partially open throttle.

Boost pressure reduction 

On certain turbocharged engines the boost pressure is controlled by a turbocharger (TC) control valve (23). It is connected to the turbocharger (TC) pressure regulator which controls the boost pressure control (BPC) valve and therefore the boost pressure. The turbocharger (TC) control valve can led off part of the boost pressure from the pressure regulator to the turbocharger (TC) inlet. This means that a relatively high boost pressure can be obtained at low engine speeds (RPM).

The control module controls the boost pressure by varying the valve opening based on information about the throttle position, load, engine speed (RPM), engine coolant temperature (ECT), and any knocking.

On certain engines the boost pressure is also affected by factors such as the gear in use, the driving mode selected and the stop (brake) lamp switch.

Pulsed secondary air injection system (PAIR) pump (not illustrated) 

Controlled via a relay.

The pulsed secondary air injection system (PAIR) pump is started by the control module and only runs for a short period after a cold start.

The pump blows air into the exhaust system immediately after the exhaust valves so that exhaust afterburning begins. This makes emissions cleaner, CO (carbon monoxide) and HC (hydro-carbons) values are reduced. This also heats the three-way catalytic converter (TWC) faster.

Gauges 

The control module sends signals to the combined instrument panel (28) with engine speed (RPM), engine coolant temperature and injected fuel quantity. The instrument panel in turn uses the information for engine speed, temperature and trip computer displays.

The speedometer (10) transmits signals about the vehicle speed and distance covered to the control module. This signal can be used by the control module to evaluate and diagnose signals from the volume air flow (VAF) sensor and control signals to the idle air control (IAC) valve.

In addition the vehicle speed signal can be used to limit the maximum vehicle speed (injection is shut off) and to calculate which gear the car is being driven in.