I had a fault on the printed circuit board of the instrument cluster, (instrument illumination had stopped working), tried to repair without success, replaced with a sh part.off ebay. All dash illumination ok now but speedo, tacho & odometer not working. Put the old on back in, same thing. Checked all fuses in fuse box in car & under bonet.Other gauges work ok, oil, temp fuel.Car starts & runs & nothing else seems to have stopped working. Help please as I am getting a headache.
Are you sure that you’ve check the fuses properly? Sounds like the METER fuse has blown.
Edit… actually, looking at the wiring diagram the oil, fuel and temperature gauges wouldn’t work either if the METER fuse had blown…
That was my first thought. I am retired but by trade am an electrician & tested all fuses in both fuseboxes. Took each one out & tested with a meter, also looked at them. It all started when the instrument lights went out, checked all fuses etc & eventually noticed a black merk on the board, looked like it had been repaired before with about 1cm of solder, which has now melted, so I soldered in a short piece of wire to bridge it. Plugged it back into the car & when I turned on the ignition, the tacho shot up to somewhere around 5000rpm, so I switched it off quickly & thought maybe I should just get a complete replacement, which I did. The seller said it was fully tested & it came from the same model/year etc MX-5 2003 MK 2.5 1.8 16v manula 5 speed, which is identical to mine.I have tried the old one back in but the tacho & odometer don’t work on that one either now.
All the warning light are ok, they come on with ignition on & go off when engine started. The car starts & runs fine. I have Googled this problem but without any success. This is actually my wifes car, I have one exactly the same model year etc but different colour which she is having to use at the moment.
I have also checked all the pins on the plugs & they all seem ok
The 12v feed for all the gauges comes off the same 12v input into the instrument cluster, the tacho and speedo are controlled by the microprocessor, the part with the LCD, in the instrument cluster from signals from the PCM. For those 3 functions only not to be working it would seem like there is a fault with the microprocessor itself. Unless for some reason you’ve lost the RPM and vehicle speed signals from the PCM…
I am pretty good mechanically with cars & have done a lot of work on both ours, but car electrics are a bit voodo to me. As I said I am an electrician by trade but used to wiring houses, not cars. Is the PCM part of the ECU? Could it have been damaged when the tacho shot up, which was rather strange as all I soldered was one wire near the plug that supplies the instrument illumination.
Yes, PCM (Powertrain Contol Module) also referred to as ECU. What’s the VIN? Are you able to check inputs to the IC (instrument cluster) with a meter if I supply you with reference values?
VIN number is JMZNB18P200315034. If you tell me which pis/plugs & the values I have a test meter so I should be able to.
Robbie, are you still there?
Yep…
Just moved to my laptop which is SLOOOOWWWW to boot up…
ok, ready when you are. Im just thinking about having a big drink if the RCU needs replacing
There are 2 plugs in the IC, the one with a Brown/Black wire at one end is connector 1 and the one with a Violet/White wire at one end is connector 2.
A few quick checks to start with…
The Blue/Red wire in connector 1 should have a permanent 12 volt feed
The Black/Yellow wire in connector 1 should have a 12 volt feed with the ignition on
The Black/Blue wire in connector 1 should be a ground
The RPM signal from the PCM goes to the IC via the Green/Orange wire in connector 2. This should be a switched 12 volt which should really be checked with an oscilloscope (got one?), but if your test meter reads RPM which some automotive ones do use that or if not, I’d basically want to see 0 volts with the engine off and some sort of voltage reading with it idling, I’d guess about 6 volts looking at the trace in the workshop manual.
Let me know how you get on with that lot.
Thank you, that may take me a while I think. I’ll get back toy you afer I print this out & check, cheers…
When you say that the odometer doesn’t work, do you mean that it doesn’t display or doesn’t count up?
The odometer doesn’t display, nothing at all. I have done the testing. Answers in next txt
All readings as you said they should be. (No RPM on meter I’m afraid) So I had to do the RPM signal the other way. There is a green & there is a green/orange & its hard to tell which is which with my old eyes but there is no volts on either with ignition off & with the engine at idle speed one has 4.7v & the other has 5.7 volts. Whats next please?
I’m fairly sure its the green/orange that has the 4.7v with engine running
The Green/Orange should be next to a Green/Red with an Orange wire next to that. Does that voltage change if you increase the engine revs?
Right I just took a pic & uploaded it. Now I can tell. Yes the green/orange is next to green/red then its orange. So it reads 5.7v when ticking over & does NOT increase when I rev the engine.