All about Ford Mondeo

Charging system - testing
Engine electrical systems / Charging system - testing

1 If a malfunction occurs in the charging circuit, donТt automatically assume that the alternator is causing the problem. First check the following items:
(a) Check the tension and condition of the auxiliary drivebelt - renew it if it is worn or deteriorated (see Chapter 1).

(b) Ensure the alternator mounting bolts and nuts are tight.

(c) Inspect the alternator wiring harness and the electrical connections at the alternator; they must be in good condition, and tight.

(d) Check the large main fuses in the engine compartment (see Chapter 12). If any is blown, determine the cause, repair the circuit and renew the fuse (the vehicle wonТt start and/or the accessories wonТt work if the fuse is blown).

(e) Start the engine and check the alternator for abnormal noises - for example, a shrieking or squealing sound may indicate a badly-worn bearing or brush.

(f) Make sure that the battery is fully-charged - one bad cell in a battery can cause overcharging by the alternator.

(g) Disconnect the battery leads (negative first, then positive). Inspect the battery posts and the lead clamps for corrosion.

Clean them thoroughly if necessary (see Section 3 and Chapter 1). Reconnect the lead to the negative terminal.

(h) With the ignition and all accessories switched off, insert a test light between the battery negative post and the disconnected negative lead clamp: (1) If the test light does not come on, reattach the clamp and proceed to the next step.

(2) If the test light comes on, there is a short in the electrical system of the vehicle. The short must be repaired before the charging system can be checked.

(3) To find the short, disconnect the alternator wiring harness: (a) If the light goes out, the alternator is at fault.

(b) If the light stays on, remove each fuse until it goes out - this will tell you which component is short-circuited.

2 Using a voltmeter, check the battery voltage with the engine off. It should be approximately 12 volts.

3 Start the engine and check the battery voltage again. Increase engine speed until the voltmeter reading remains steady; it should now be approximately 13.5 to 14.6 volts.

4 Switch on as many electrical accessories (eg the headlights, heated rear window and heater blower) as possible, and check that the alternator maintains the regulated voltage at around 13 to 14 volts. The voltage may drop and then come back up; it may also be necessary to increase engine speed slightly, even if the charging system is working properly.

5 If the voltage reading is greater than the specified charging voltage, renew the voltage regulator (see Section 13).

6 If the voltmeter reading is less than that specified, the fault may be due to worn brushes, weak brush springs, a faulty voltage regulator, a faulty diode, a severed phase winding, or worn or damaged slip rings. The brushes and slip rings may be checked (see Section 13), but if the fault persists, the alternator should be renewed or taken to an auto-electrician for testing and repair.

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