Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Speedometer not working on 2008 Plus 4

It turned out that the speed sensor attached to the gearbox is out of production and hard to get. All new cars use an ABS wheel sensor to get input to the speedometer. Last week a new gearbox speed sensor arrived and was fitted, but the speedometer still does not work. The PCB was the problem. Now I am waiting for a new PCB from England.

Harald

Sorry to hear that Harald but at least the good new is that it sounds like these pcb are still available. I assume it's a faulty MFU pcb rather than the notorious dash pcb?

Yes, it was a faulty MFU pcb. I picked up the car today, and now the speedometer is working again.

Harald

That's good news Harald, back on the road again

Do you mind me asking a question, did the MIL light also come on when the speedo conked out?

I used the car with a Garmin Navigation unit with a built-in speedometer while waiting for the parts. It worked well except in tunnels.

No, there were no MIL warning light, while the speedometer was inoperative. I can't help thinking that the speedometer should be independent of a PCB: just a speed sensor connected by directly to the speedometer with all electronics built into the instrument itself.

Harald

Yes I agree Harald, I think the speedo should be independent too, however our cars may be a bit over complicated.

Unfortunately the speed sensor signal is sent to MFU pcb where the signal appears to be split before being sent to both the speedo and the vehicle speed input on the ECU (pin 58). I'm speculating that the vehicle speed input to the ECU might be unnecessary on our Morgans. Why? On the donor vehicle where this ECU is normally used (MK3 Mondeo's) this speed signal is used to manage the auto transmission and cruise control functionality, neither of which our Morgans have as an option. Also when the speed signal is lost on those vehicles, the ECU typically throws an error code. So I was curious to see if your lost signal had disrupted the ECU, hence my asking if the MIL light came on.

I speculate this could be wired simpler avoiding the MFU