Electrics: Hold Light irregular Flashing, Speedo not working

[Kernowel]

Hi all Merry Xmas, etc!

Went out cold this morning and the gearbox HOLD light started irregular flashing as if a loose wire was causing it. The gearbox was not in Hold at all and the Hold button was not responsive (i.e. I couldn't get it into Hold if I wanted to). Also the Speedo was not working (Rev Counter was working). The engine and gearbox were running as normal. So I thought it must be an electrical fault. I stopped & restarted and the problems all went away and haven't returned today. No doubt they will return soon.

Any ideas what is occurring?

Cheers
H

[g8dhe]

Yes the ECU reports that there is a fault by flashing the Hold light, you then need to readout from the diagnostic socket the actual errors that are being reported. If your a member then see the Fact Sheet in the members area or there is a web site that gives some info on early models http://www.philmcfadden.co.uk/MazdaDiagnosticBox.htm

The speedometer is an important input to the ECU so if that wasn't sending a signal to the ECU & Speedometer gauge that is likely the problem, possibly a poor connection etc. the actual sensor is at the output shaft end of the gearbox.

[bazzog]

I had a similar problem with the rev counter working intermittently and speedo being erratic then they both stopped working, I ordered a ne sensor from aliexpress about £12 , takes 5 minutes to swap and had no problems since

[Kernowel]

I had a similar problem with the rev counter working intermittently and speedo being erratic then they both stopped working, I ordered a ne sensor from aliexpress about £12 , takes 5 minutes to swap and had no problems since

Hi Bazzog - I will give that a go. If you have got a link to the Aliexpress item, that would be ideal. Otherwise I will have a look at finding out what I need to order.
Cheers
H

[Kernowel]

Yes the ECU reports that there is a fault by flashing the Hold light, you then need to readout from the diagnostic socket the actual errors that are being reported. If your a member then see the Fact Sheet in the members area or there is a web site that gives some info on early models http://www.philmcfadden.co.uk/MazdaDiagnosticBox.htm

The speedometer is an important input to the ECU so if that wasn't sending a signal to the ECU & Speedometer gauge that is likely the problem, possibly a poor connection etc. the actual sensor is at the output shaft end of the gearbox.

Many thanks for the advice. I thought the ECU reports faults by flashing the Glow Plug light not the Hold light? Yes I am a member. I have checked the Diagnostic Factsheet but have to admit I find these things a little bit daunting to do myself. Looks like I need to interpret the pulses using a volt meter and an earthing lead. Nothing is ever straightforward is it !

[Kernowel]

I think I have found an explanation on the Clinic questions under speedo. I will pass that to my Bongo engineering team! If I try and fix this I will probably end up disrupting the time/space continuum or worse!


A: Commonly, if the speedo is not ‘chipped’ (speedo reads in kms or miles, odometer reads in kilometres), this is caused by a bad earth or loose connection, so check the connections behind the speedo. If there is a chip fitted (both speedo and odometer read in miles) then the chip is commonly faulty. You either need to replace it or remove it, reconnect the cables and change the speedo face again. (Allans Vehicle Services).
“Grumpo” reports:- The speedo is driven by a low voltage square wave frequency generated by the gearbox transmitter. As it’s virtually impossible for anything else to simulate this signal I can only assume that that the speedo head can also respond to a DC voltage and drive it full scale. If this was the case then you should also get a hold light error, flashing 1 second ON and 1 second OFF, although a DC signal may confuse it.
If your odometer reads in MILES then a frequency converter “Chip” must be fitted behind the instrument panel and I would suspect that this is faulty and sending DC on the output to the speedo. I would not suspect anything prior to the “Chip” because the circuit only responds to the rising edge of the frequency and it would not pass a DC voltage if it was in good condition.
If you do have a converter “Chip” fitted I would first remove this and re-connect the original cables, this will then convert the speedo back to reading kilometers and with a bit of luck solve the problem.
If you don’t have a “Chip” fitted and your odometer reads Kilometers then you will have to use an oscilliscope to test the actual input to the speedo head to determine if the speedo head or gearbox unit is the faulty part. A modern electronic volt meter would not reliably block the DC component whereas an old moving iron meter may give you some indication.

[g8dhe]

Ah you didn't say what engine you have! Diesel yes it flashes the Glowplug, Petrol engines it flashes the Hold light as there isn't a glowplug!