Battery warning light
About two months ago, the battery warning light came on while I was driving my 2009 Ford Focus Titanium 2.0 diesel. I carried on for three miles to the next available place to stop, but when I tried to restart the engine, the battery was totally dead. I phoned the RAC, which diagnosed a faulty alternator that had overcharged the battery and destroyed it – the battery was actually quite hot to the touch. The RAC man disconnected the alternator, fitted his spare battery and escorted me to my local garage, which fitted a new alternator and battery. Ever since this happened, whenever the lights are switched on they flicker from bright to dim; they never go out completely, just alter in intensity. All the lights are affected: sidelights, headlights, rear lights and interior lights. Revving the engine lessens the flicker, but it doesn’t stop completely. If I turn off the engine, the flickering stops. I have been back to the garage that fitted the alternator and battery, but they assure me that neither the battery nor the alternator are at fault.
Malcolm Thomas
Your Ford Focus is fitted with a smart charge system that relies not only on the alternator to charge the battery, but also on the engine control module to regulate the charge. The flickering lights are usually an indication of an alteration in the charge rate or a charging ripple from the alternator.
I am assuming that the garage has fitted the correct battery, which should be a silver calcium type and not standard lead acid. Provided this is correct, I suspect that there is a problem with either the charging system or its connections. The smart charge system can produce up to 18 volts and, if the battery has been overcharged, then this excess voltage may also have caused damage to the engine control module.
The first test to carry out would be to check the charging voltage. I suspect that if the lights are flickering then the voltage will also be fluctuating. If this is the case, you will have confirmed that there is a fault in the charging system that needs to be rectified. Even if no alteration in voltage is detected, the alternator charging system should be checked using an oscilloscope to ensure the waveform is correct.