What's wrong with my Ford Focus?
I have a 2006 Ford Focus estate. I'm having a problem that no one seems to be able to figure out. The battery light comes on and the car dies a while after. I then use my booster pack to start it and it goes for a day or two until it happens again.
Since this has started the battery and alternator have been replaced but I still have the same problem. The modules have been done, the thermostat too. My mechanic cannot figure out what it is.
When the battery light comes on, the car is sluggish, chugging and goes to cut out.
I'm at my wits end.
Dana Forde (Dublin 15)Mar 2025 Filed under: fault
Expert answer
Hi Dana,
It really sounds related to the charging circuit and, before going through the list below, perhaps check that the battery was replaced by a 'silver-calcium' one that is compatible with the so-called “Ford Smart Charge System”. A regular lead-acid battery is not compatible.
We'd have hoped that a good mechanic would have tried the below things already, but if not:
Bad ground or wiring issue
- A poor ground connection or corroded cables can cause intermittent charging problems.
- Check and clean all ground connections (especially the engine-to-chassis ground and battery-to-body ground).
- Look for damaged or frayed wiring between the alternator, battery and fuse box.
Alternator not charging properly
- Even new alternators can be faulty. A voltage drop test should confirm if it's truly charging.
- With the engine running, check the voltage at the battery terminals. It should read around 13.5-14.5 volts.
- If it's much lower, the alternator isn't charging properly, or something is disrupting the circuit.
Smart Charge System
- The Ford Smart Charge system can fail and cause charging problems.
- Check the three-pin connector going to the alternator - if it's loose, corroded, or damaged, the alternator may not work correctly.
- Try disconnecting the Smart Charge system (forcing the alternator to work as a standard one) and see if the problem improves.
Parasitic battery drain
- If something is drawing power while the car is off, the battery might not have enough charge when you restart.
- A mechanic can do a parasitic draw test by pulling fuses one by one to find a circuit draining power.
Faulty ECU or sensors
- If the ECU isn't regulating voltage properly, it could be sending the wrong signals to the alternator.
- Some Ford owners have reported a faulty crankshaft position sensor or bad engine ground causing similar symptoms.
Fuse box or relay issue
- Check the engine bay fuse box for water damage or corrosion - this is common on older Fords.
- A failing alternator fuse or relay could intermittently stop charging.