Battery light in Fiesta 1.6: Ford Service centre suspects faulty ECU

They checked the alternator and it seems to be fine. Now they are suspecting that there is an issue with the PCM (ECU). A new PCM will cost Rs 35 K.

BHPian pramodpk recently shared this with other enthusiasts.

The battery light stays on in my Ford Fiesta 1.6 petrol. The car is 14 years old and has done 1.26 Lakh KMS. Currently the car is at Ford service station. They checked the alternator and it seems to be fine. Now they are suspecting that there is an issue with the PCM (ECU). A new PCM will cost Rs 35 K. Is there anything else to check?

Thanks in advance.

Here's what BHPian TheVDR had to say about this matter:

Old Battery - Old Alternator; New Battery - Old Alternator; Old Battery - New Alternator; New Battery - New Alternator. This is the SOP to check as Battery and Alternator works both ways. If none of these work, check for all loose wiring, remove sensors - clean dirt - put back sensors. Check OBD.

Pretty sure Ford must have done all this before concluding a PCM error. But if it's worth 35k, then it's worth asking them to redo. Also, what are the fault codes? Is ECU itself showing a fault code? I know couple of cases where something as petty as dirt on the air mass flow sensor caused a check engine light and/or a battery light (possible short-circuit? Nobody knows!) But got resolved as with some cleaning. My fiesta was notorious for troubles with its Lambda (Oxygen) sensor. Worth a look!

Lastly, if ECU replacement is the last resort then it can be swapped. Although it is not advisable to reuse an old ECU (from an identical variant car), given your car is already 14 years old, it maybe worth a shot. ASS won't do it (obviously) but it can be done aftermarket. It can be reprogrammed to your VIN too. Again, not a 100% solid thing to do, but given the age of the car and the cost it can save (north of 20k!), it is definitely worth a shot.

Meanwhile, here is BHPian NomadSK's reply on this:

Regardless of what symptoms you’re noticing, the battery light is telling you a simple truth: you have either battery or charging problems,

It can be any of this;

• A loose or corroded battery cable/terminal
• A problem with the alternator or voltage regulator (Overcharging/Undercharging, most Likely, have happened twice with me)
• Damaged cells inside the battery or low electrolyte (Check battery condition)
• Faulty wiring in the car's electric charging system (leaking current)
• Damaged fuse

Older the car more is the probability of the above issues.

But mostly nothing to do with ECU, plug in the OBD scanner to find out.

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