Engine management system - EDC (Cooling Strategy): Description and operation

Cooling Strategy

The ECM controls cooling fan operation for the engine, automatic gearbox and A/C condenser. With the ECM controlling cooling fan operation, it can adjust injection duration and timing to compensate for additional engine load imposed by the alternator during cooling fan operation. The ECM can request one of three fan speeds depending on coolant temperature, EAT ECU and A/C requests. These fan speeds are: l Low: 250 rev/min. l Medium: 800 rev/min. l High: 1750 rev/min.

Priority will be given to the highest fan speed request. When A/C is requested, fan speed is set to low, unless the EAT ECU or ECT requires a higher fan speed. If the cooling request circuit of the trinary switch is open the fan speed is then set to medium. High speed fan operation will be selected by one of the following conditions: l Engine temperature is greater than 119 °C (246 °F). l EAT ECU request for increased cooling.

The ECM achieves fan speeds by sending a 140 Hz PWM signal to a PWM converter located within the fan relay module. The PWM converter is connected to three relays, also located within the fan relay module, and determines which relays to energise by the duty cycle of the pulse: l 13%: Relay one energised to give low fan speed. l 40%: Relays one and two energised to give medium fan speed. l 86%: Relays one, two and three energised to give high fan speed.

Electronic Automatic Transmission (EAT) ECU Strategy

On automatic gearbox models, the EAT ECU implements an idle neutral strategy, which is part of the fuel reduction strategy. Neutral is selected, reducing engine load and fuel consumption, when all of the following conditions are met: l ECM confirms engine at idle. l 'D' selected on gear selector lever. l Foot brake applied.

Should one of these conditions change, after neutral has been selected, 'D' will be reselected automatically.

When the EAT ECU requests, via the CAN bus, a reduction in engine torque, the ECM reduces engine torque by cutting back fuel delivery. This ensures smooth gear changes throughout the engine speed and load ranges, and reduces exhaust emissions.

Information sent from the ECM to the EAT ECU using the CAN bus is as follows: l Accelerator pedal position. l Engine torque. l Engine speed. l Coolant temperature. l Ignition key position. l Virtual 'throttle' angle.

Information sent from the EAT ECU to the ECM using the CAN bus is as follows: l Torque reduction requests. l Gear lever position. l Current gear. l Gear change in progress. l Additional cooling request.

Immobilisation System

The ECM plays a major role in the immobilisation of the vehicle. The ECM inhibits engine fuelling until the ECM receives a valid coded signal from the immobilisation ECU. The coded signal from the immobilisation ECU comes in the form of a rolling code. This code cannot be copied or bypassed in any way.

When new, the immobilisation ECU is blank and is programmed with a starting code known as a 'seed'. The seed is then used as a base point for the rolling code when the immobilisation ECU is synchronised to the ECM during manufacture.

Once synchronised, the ECM and immobilisation ECU are not interchangeable and work as a matching pair.

When a new ECM is fitted to a vehicle during service, the new ECM must be in a blank condition. The blank ECM must be re-synchronised to the immobilisation ECU using TestBook.