My recently acquired 2004 1.6 (mark 2.5 I suppose) had a problem just after I got it that revving the made the lights get brighter, the abs and airbag lights come on and the stereo switch off. Then it got better by itself…
2 months later it’s back. I reckon the fault must be in the alternator, ecu or the wiring/connectors between them. I refitted the engine earth strap (could only find 1 strap) and the fault got a bit better but still after that i revved it and blew a main beam bulb. Apart from this the car is OK and if you never drove above 2000rpm you wouldn’t see the fault.
I’ll be checking the wiring and connectors tomorrow once I bring a DMM home…but if there is a problem with the alt or ecu it could get really expensive really quickly and cause me real tears.
Really hoping someone else has seen this…have searched all forums but none the wiser. Grateful for any comments, thanks!
Sounds like the voltage regulator is faulty. I seem to recall that the Mk2 is unusual in as much as the voltage regulator is built into the ECU rather than being included in the rectifier pack in the alternator.
Funny thing is it’s working OK again this morning. Going to look for a loose connection particularly the two wires that come to the alternator from the ECU (PCM). Can’t get a manual for this car which makes things tricky but from web searches I think the ECU may be under a metal plate under the carpet in the passenger footwell. Even if don’t find anything I don’t see how a fault can’t be in the alternator end of things just as it might be in the ECU end. If I eventually have to go down the ECU replacement route that will be a worry due to keys etc. Daren’t go near Mazda as don’t have any confidence in dealers not to turn a niggly fault into a financial disaster zone!
The PCM is in the passenger footwell but is protected by shear bolts so is not that easy to gain access to. Be aware, PCM faults are extremely rare on MX-5, I’d certainly want to eliminate alternator/wiring before condeming a PCM. If I couldn’t find anything external I’d certainly try a 2nd hand alternator before going down the PCM road. I’ve changed more alternators than PCM’s in my time.
Also, if you can find someone with a code reader, the PCM will/may store fault codes for alternator faults.
thanks that’s good to hear also didn’t know about the shear bolts. It’s working fine again tonight. When it stops raining I’ll do some wiring checks. Certainly would exhaust the alternator possibilities first I wonder if I can access the PCM connector perhaps not…
Torrential rain this morning. Went thru a real deep puddle by mistake. All the symptoms popped up immediately: lights brighter, stereo cut out, ABS light, exclamation mark light and battery light came on, airbag light flashing. Pulled over and waited a few minutes. Eventually it all calmed down and I drove on. Recall at the weekend I threw a bucket of water over the bonnet after washing the car and then the next time I started it a few hours later this trouble all started. Is it possible that triggered this whole episode? Remember it happened when I first got the car then went away by itself and never showed up for 2-3 months till last weekend and the car washing/bucket of water over the bonnet/wipers/scuttle area.
Real keen to hear any opinions. Also want to investigate connectors behind the engine also passenger footwell and take off the cover plate over the ECU. Could I have a blocked or broken scuttle (by this I mean the black area between the windscreen and the bonnet) drain that is diverting water elsewhere? Need to get onto this before the salty road water appears or will have a real problem am sure.
Real interested in any car washing/driving thru deep puddles stories/advice, thanks in advance.
BTW if you think my theory is nonsense feel free to say so! Dave.
