Thanks for that 2sticks. Actually the dealer suggested a new chip at his cost.
Cheapest solution probably.
I've checked all the chip connections as tight but one point labelled as ECU out is not connected suggesting that the input to the ECU is direct from the speed sensor aft of the gearbox and not via the speedo(unless the dealer got it wrong and it should be connected!)
When it going to do its stuff the first sign is no speedo followed correctly as you said after a few yards as a flashing hold light. The diagnostic check shows "speed sensor".
Thanks for your expert input but as a vain effort we'll go for a chip change first at the dealers expense. Any idea of the cost of a speed sensor?
Bonz
Speedo - is this a problem?
Moderators: Doone, westonwarrior
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Colin Lambert
-
Bonza
Thanks Colin. I meant the price of the mazda speed sensor fitted near the gear box!
What gets me is that having got the fault, I just stop, switch off, restart and all is well.
Puzzled.
Only thing thats been touched since she came from Japan is adding a chip to the speedo. Thats the first thing to look at I think.
What gets me is that having got the fault, I just stop, switch off, restart and all is well.
Puzzled.
Only thing thats been touched since she came from Japan is adding a chip to the speedo. Thats the first thing to look at I think.
Speed sensor.
The price for a gearbox speed sensor has been quoted on the forum
somewhere but I can't remember how much, Probably + 100 pounds.
The ECU uses the gearbox sensor to recognise that the vehicle is
actually moving, and compares this signal with the same one from
the speedo head to check the speedo.
Using a bit of logic here:
If the gearbox sensor is not working then the ECU would not know
the vehicle is actually moving, there would also not be a signal from
the speedo head, so effectively you should not get a hold light error.
As a point of interest, when the hold light flashes for this error, it locks
on even though an intermittant fault may have recovered. If you slow
down to less than 10 MPH, the ECU then checks the signals again and
switches the hold light off after a few seconds if all is OK.
If you still suspect the chip is faulty then you could simply remove it
and run on Kilometers for a few days to check it. As an after fitting
the 2 standard wires are normally broken and the original connections
are easily identified. there should be an additional +/- 12 volt supply
going to the chip which can remain in place, or insulated if you
completely remove the IC.
I would definitely try this before going to the expense of a new
gearbox sensor which may not be the problem.
somewhere but I can't remember how much, Probably + 100 pounds.
The ECU uses the gearbox sensor to recognise that the vehicle is
actually moving, and compares this signal with the same one from
the speedo head to check the speedo.
Using a bit of logic here:
If the gearbox sensor is not working then the ECU would not know
the vehicle is actually moving, there would also not be a signal from
the speedo head, so effectively you should not get a hold light error.
As a point of interest, when the hold light flashes for this error, it locks
on even though an intermittant fault may have recovered. If you slow
down to less than 10 MPH, the ECU then checks the signals again and
switches the hold light off after a few seconds if all is OK.
If you still suspect the chip is faulty then you could simply remove it
and run on Kilometers for a few days to check it. As an after fitting
the 2 standard wires are normally broken and the original connections
are easily identified. there should be an additional +/- 12 volt supply
going to the chip which can remain in place, or insulated if you
completely remove the IC.
I would definitely try this before going to the expense of a new
gearbox sensor which may not be the problem.
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Bonza
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Bonza
Quote-
"If the gearbox sensor is not working then the ECU would not know
the vehicle is actually moving, there would also not be a signal from
the speedo head, so effectively you should not get a hold light error."
So, if the speed sensor fails what is used to arm the ECU to say its actually failed? Does the ECU get a feed from something else to arm the speed sensor monitor circuit? Curious!
"If the gearbox sensor is not working then the ECU would not know
the vehicle is actually moving, there would also not be a signal from
the speedo head, so effectively you should not get a hold light error."
So, if the speed sensor fails what is used to arm the ECU to say its actually failed? Does the ECU get a feed from something else to arm the speed sensor monitor circuit? Curious!
Bonza,
To be honest I haven't gone that far so the following is
pure supposition.
The ECU checks dozens of things, most of which do not
rely on whether the vehicle is moving or not, after all, the
only things it could check is whether the wheels are going
round or not.
There has to be some point when the software has to rely
on a final sensor to do it's job properly, and if this fails then
to hell with it, hopefully it will last until the guarantee runs out
and it's not a major safety feature anyway.
Cynical I know, but it does often happen, because you would
have to keep adding more sensors simply to check the following
ones are still working, that would be an even worse nightmare.
What I will do if I get the time, is to disconnect the gearbox
sensor and suck it and see. I am also curious.
To be honest I haven't gone that far so the following is
pure supposition.
The ECU checks dozens of things, most of which do not
rely on whether the vehicle is moving or not, after all, the
only things it could check is whether the wheels are going
round or not.
There has to be some point when the software has to rely
on a final sensor to do it's job properly, and if this fails then
to hell with it, hopefully it will last until the guarantee runs out
and it's not a major safety feature anyway.
Cynical I know, but it does often happen, because you would
have to keep adding more sensors simply to check the following
ones are still working, that would be an even worse nightmare.
What I will do if I get the time, is to disconnect the gearbox
sensor and suck it and see. I am also curious.
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Peg leg Pete
- Supreme Being
- Posts: 2910
- Joined: Thu Aug 25, 2005 7:07 pm
- Location: Yorkshire
I will have a look at the weekend, and let you know how I get on 
Pete