Mil light with mind of its own. Focus st170

Hi all,

Got a weird issue here, got a 2003 ST170. The MIL light keeps coming on, usually at cold start. Then will flicker and go off after a few mins.
Today I checked my engine coolant and found the bottle almost empty so I filled the coolant up, restarted the engine and the light come back on lol !!

Now, I have just scanned the ecu with my ELM327 using both easyobd and PCMSCAN. Both say ECU faults are clear, even when I cold started the engine and the light was on.... laptop reported no MIL.

Ive noticed no loss of power, or anything else really. Other than a slight squeak when engine is running and the loss of coolant (which I think could be thermostat housing as the metal bung thing was leaking a while back but I used sealer as a temp fix)


Any ideas peeps ? anyone encountered this before cos I am lost at where to start on this one.


Ty in advance all.

TBH, could be almost anything lol First, the MIL comes on when ANY sensor in the engine management array shows a fault i.e. lambda, MAF, coolant temperature etc. If there's no loss of performance it could be a sign a sensor is on its final journey or something is reacting a bit sluggishly at startup. Before exposing your wallet I would try a few simple things:

1 - ensure your code reader will read ALL codes on this model (some readers don't see some proprietary codes although OBDII should get them all)
2 - check electrical connections to common sensors (MAF, coolant and lambda etc)
3 - this model has known issues with lambda sensors so a good check of those (I'm NOT an expert but I beleive there's two, one before and one after the CAT)

On the other hand, the fact it goes out after a few minutes will make it hard to nail so you might just monitor it until it comes on permanently? It may be an intermittent sensor fault. It may be that the ECU doesn't show a code because of the way it responds to sensor input i.e. the fault usually has to persist for a while before it gets recorded.

Good Luck!

Cheers pal.

Yeah there is two lambda sensors. I will check the plugs. My lead is a obdII Elm lead.
I think I'm going to wd40 the common connector plugs in case it's moisture or something I think.

Cheers.
Bill