All about Ford Mondeo

General information, precautions and battery disconnection
Engine electrical systems / General information, precautions and battery disconnection

General information
The engine electrical systems include all ignition, charging and starting components.

Because of their engine-related functions, these components are discussed separately from body electrical devices such as the lights, the instruments, etc (which are included in Chapter 12).

Always observe the following precautions when working on the electrical system: (a) Be extremely careful when servicing engine electrical components. They are easily damaged if checked, connected or handled improperly.

(b) Never leave the ignition switched on for long periods of time when the engine is not running.

(c) Dont disconnect the battery leads while the engine is running.

(d) Maintain correct polarity when connecting a battery lead from another vehicle during jump starting - see the Booster battery (jump) starting section at the front of this manual.

(e) Always disconnect the negative lead first, and reconnect it last, or the battery may be shorted by the tool being used to loosen the lead clamps (see illustration).

1.2 Always disconnect battery - negative (earth) lead first - to prevent the
1.2 Always disconnect battery - negative (earth) lead first - to prevent the possibility of short-circuits

Its also a good idea to review the safetyrelated information regarding the engine electrical systems located in the Safety first! section at the front of this manual, before beginning any operation included in this Chapter.

Battery disconnection
Several systems fitted to the vehicle require battery power to be available at all times, either to ensure their continued operation (such as the clock) or to maintain control unit memories (such as that in the engine management systems ECU) which would be wiped if the battery were to be disconnected. Whenever the battery is to be disconnected therefore, first note the following, to ensure that there are no unforeseen consequences of this action: (a) First, on any vehicle with central locking, it is a wise precaution to remove the key from the ignition, and to keep it with you, so that it does not get locked in if the central locking should engage accidentally when the battery is reconnected!

(b) The engine management systems ECU will lose the information stored in its memory - referred to by Ford as the KAM (Keep- Alive Memory) - when the battery is disconnected. This includes idling and operating values, and any fault codes detected - in the case of the fault codes, if it is thought likely that the system has developed a fault for which the corresponding code has been logged, the vehicle must be taken to a Ford dealer for the codes to be read, using the special diagnostic equipment necessary for this (see Chapter 6). Whenever the battery is disconnected, the information relating to idle speed control and other operating values will have to be re-programmed into the units memory. The ECU does this by itself, but until then, there may be surging, hesitation, erratic idle and a generally inferior level of performance. To allow the ECU to relearn these values, start the engine and run it as close to idle speed as possible until it reaches its normal operating temperature, then run it for approximately two minutes at 1200 rpm. Next, drive the vehicle as far as necessary - approximately 5 miles of varied driving conditions is usually sufficient - to complete the relearning process.

(c) If the battery is disconnected while the alarm system is armed or activated, the alarm will remain in the same state when the battery is reconnected. The same applies to the engine immobiliser system (where fitted).

(d) If a trip computer is in use, any information stored in memory will be lost.

(e) If a Ford Keycode audio unit is fitted, and the unit and/or the battery is disconnected, the unit will not function again on reconnection until the correct security code is entered. Details of this procedure, which varies according to the unit and model year, are given in the Ford Audio Systems Operating Guide supplied with the vehicle when new, with the code itself being given in a Radio Passport and/or a Keycode Label at the same time. Ensure you have the correct code before you disconnect the battery. For obvious security reasons, the procedure is not given in this manual. If you do not have the code or details of the correct procedure, but can supply proof of ownership and a legitimate reason for wanting this information, the vehicles selling dealer may be able to help.

Devices known as memory-savers (or code-savers) can be used to avoid some of the above problems. Precise details vary according to the device used. Typically, it is plugged into the cigarette lighter, and is connected by its own wires to a spare battery; the vehicles own battery is then disconnected from the electrical system, leaving the memory-saver to pass sufficient current to maintain audio unit security codes and ECU memory values, and also to run permanentlylive circuits such as the clock, all the while isolating the battery in the event of a shortcircuit occurring while work is carried out.

Warning: Some of these devices allow a considerable amount of current to pass, which can mean that many of the vehicles systems are still operational when the main battery is disconnected. If a memory-saver is used, ensure that the circuit concerned is actually dead before carrying out any work on it!

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