Charging system
The battery light in my 2004 Ford Ka comes on a few seconds after starting and stays on. I am fairly handy with electrics, but don’t know how to identify the wires at the plug on the right-hand side of the alternator, looking towards the back. The plug is visible, but it would be difficult to remove with the bumper in place. I am not keen on taking half the car apart to remove the alternator unless absolutely necessary.
The voltage across the battery is 15 volts with the engine running and no extra electrics. With everything on – fan, lights, heated rear screen, etc – the voltage drops to 14.7V. Paul Procter The problem may be within the alternator or the smart charge system. Disconnecting the plug from the back of the alternator will disconnect the smart charge system and revert the alternator back to a standard charging unit. As your alternator is charging, the test does need to be done at the alternator and PCM.
The first test is to ensure that you have full battery voltage present at terminal three of the plug. This will be the orange and yellow wire in the loom. The voltage must match the battery voltage, confirming there is no resistance in the circuit. If the voltage does not match, check the fuse and connections, which may simply need cleaning.
Next, check for any resistance in the two wires from pins 1 and 2 to the PCM. The wire to terminal 1 should be grey and that to terminal 2 is blue. The next test needs to be done using a oscilloscope. With the plug connected and the engine running, place the test probe into the back of terminal 2 and you should see a square wave pattern. Turning on a load – such as the HRW – should change the pattern. If there is no change in pattern, this will confirm that the PCM is at fault. If the wave pattern does change, then check pin 1 in a similar way; this pattern should not change. If it does alter under load, it will mean the alternator is faulty. I appreciate that access to the plug is difficult, but this is the only way to confirm the source of the problem.