Jaguar XJ (X350). Manual — part 1271

following measurements may not apply.

Disconnect the battery ground cable. <<414-01>>

2. Check the vehicle off-load battery voltage. If below 12.5 volts, install a fully charged slave
battery for the tests and recharge the vehicle battery.

3. Connect a suitable ammeter to the battery with the negative test lead clip to the negative
battery terminal, and the positive test lead clip to the battery negative lead.

4. NOTE:

Make sure that all electrical accessories are switched off.

Operate the key fob unlock button to disarm the vehicle security system.

•

Switch the ignition to the RUN position for a 10 second duration.

•

Switch the ignition to the OFF position. Remove the key.

•

Close the vehicle doors and luggage compartment lid.

5. Monitor the ammeter reading for 30 minutes.

6. After 30 minutes the quiescent current reading should be no greater than 30 milliamps.

7. Disconnect the ammeter. Reconnect the battery ground cable. <<414-01>>

Description and operation

Charging System

The charging system for vehicles fitted with a 3.0L engine consist of a 120 amp L3B generator.

Vehicles fitted with a 3.5L or 4.2L engine consist of a 130 amp SC1 generator. Vehicles fitted with a

2.7L Diesel engine consist of a 150 amp SC2 generator. The generator and regulator assembly

generates current to supply the vehicle electrical system with electricity when the engine is running

and maintain the battery in a charged state.

The generator is belt driven by the accessory drive belt. For additional information, refer to

Accessory Drive (303-05)

When the engine is started, the generator begins to generate alternating current (AC) which is

converted to direct current (DC) internally. The DC current and voltage is controlled by the voltage

regulator, (located inside the generator) and then supplied to the battery through the main battery

positive cable.

The 3.0L generator is solidly mounted to the engine, while the 3.5L and 4.2L generator is pivot

mounted. The 2.7L Diesel generator is also solidly mounted to the engine. The generators are driven

at approximately three times engine speed.

Vehicles fitted with 3.0L engine (L3B generator)

The engine control module (ECM) can switch the voltage regulator between two voltages to optimize

the charging of the battery.

The low voltage regulator setting is 13.6 volts and the high voltage regulator setting 15.3 volts,

measured with the generator at 25°C (77°F) and charging at a rate of 5 amps. These values decrease

with a rise in temperature or current flow.

The ECM determines the output voltage setting of the generator. The high voltage setting is always

selected by the ECM once the vehicle has started. The ECM determines the period of time that the

high voltage setting is selected for.

There are three different time periods selected by the ECM which is dependent upon the vehicle

conditions when the vehicle is started:

•

The longest period of time is selected if the ECM determines that the vehicle has been
'soaking' for sufficient time to allow the engine coolant temperature (ECT) and the air intake
temperature (IAT) to fall within 6°C (43°F) of each other.

•

The intermediate time period is selected when the ECT and the IAT are below 15°C (59°F).

•

The shortest time period is the default time and is used to provide a short period of boost
charge.

www.

At the end of these time periods the voltage is always set to the low voltage setting to prevent the

battery from being over charged.

The time periods are variable depending upon the temperature and battery voltage. The target

voltage of the battery varies between 14 volts and 15 volts depending upon the ambient

temperature and the vehicle operating conditions. Once this target voltage has been achieved,

providing the vehicle has been operating for at least the shortest time period, the ECM will reduce

the voltage regulator to the minimum setting of 13.6 volts.

Vehicles fitted with 3.5L or 4.2L engine (SC1 generator)

The battery charging voltage is determined by the temperature of the generator. In cold conditions,

starting the vehicle from cold the battery voltage will be between 14.2 volts and 15.1 volts and will

reduce as the engine warms up. In hot conditions starting the vehicle when the engine is already

warm the battery voltage will be between 13.5 volts and 14.3 volts.

A fault in the wiring or the connections from the generator to the ECM, will cause a fault code to be

generated and stored in the ECM and the charge warning indicator lamp to be displayed in the

instrument cluster after a short time.

With the ignition switch in the RUN position the charge warning lamp will be displayed in the

instrument cluster when the generator is not generating power.

If a fault is detected with the generator a fault code will be generated and stored by the ECM. The

charge warning indicator lamp will also be displayed in the instrument cluster. Units should be

repaired as an assembly and not dismantled for repair. For additional information, refer to

Generator (414-02)

Vehicles fitted with 2.7L Diesel engine (SC2 generator)

All vehicles use a PCM (Pulse Control Modulated) generator. This allows the output voltage to be

controlled between 12.5 volts and 16 volts via a signal from the ECM.

This voltage is controlled between 13.5 volts & 15.5 volts. The system voltage is tailored more closely

to the demands of the battery. At low ambient temperatures (as measured by the air conditioning

ambient air sensor), the charging voltage is higher to improve charge acceptance. At high ambient

temperatures the voltage is lower to reduce electrolyte loss and unnecessary battery self-heating.

Also built into the strategy, is the ability to measure the battery voltage with the ignition switch in

the ON position. A battery with low voltage, with the ignition switch in the ON position, is boost

charged at a higher voltage for a calculated time before returning to its 'Base Characteristic' (defined

by the prevailing ambient temperatures). The time and boost voltage depends upon the temperature

and battery voltage with the ignition switch in the ON position.

All vehicles have a one way clutch fitted to the drive pulley, which reduces belt slip.