Discussion
Have had my chim for about 3 weeks now, a 1998 4.0L.
The speedo became intermittent over the last week or so, but has now given up all together.
I have looked at the output from the sensor and this appears to be ok. (oscilloscope across the output terminals)
However looking at the bible cicuit diagram the sensor should be supplied with 12volts from the ignition
switch on one side.
However neither wire connected to the sensor has any voltage at all. (one grey and one black)
Can anyone please tell me where the voltage is supplied from, again the bible says it could be the same fuse as the brake lights or the reversing lights, both of which are working fine.
Also what route does the sensor wire take, does it come up into the cabin behind the fuel tank or behind the seats.
Any help or advice would be much appreciated.
Thanks Paul.
The speedo became intermittent over the last week or so, but has now given up all together.
I have looked at the output from the sensor and this appears to be ok. (oscilloscope across the output terminals)
However looking at the bible cicuit diagram the sensor should be supplied with 12volts from the ignition
switch on one side.
However neither wire connected to the sensor has any voltage at all. (one grey and one black)
Can anyone please tell me where the voltage is supplied from, again the bible says it could be the same fuse as the brake lights or the reversing lights, both of which are working fine.
Also what route does the sensor wire take, does it come up into the cabin behind the fuel tank or behind the seats.
Any help or advice would be much appreciated.
Thanks Paul.
The sensor is passive so no current is supplied to it.
If you google 'inductive proximity sensor' you can find out how it works.
If you search the word speedo on this forum and on the general TVR forum you will find
quite a few threads. Sensor failure appears to be the most common cause of speedo problems.
The gapping of the sensor to the toothed wheel is fairly critical. Clean your sensor and wheel and re-set the gap to eight thou' using a feeler gauge and see if this makes any difference.
Check out this thread www.pistonheads.com/gassing/topic.asp?h=0&t=240993&p=1 and the ones linked to it
>> Edited by sparkythecat on Sunday 19th March 15:52
If you google 'inductive proximity sensor' you can find out how it works.
If you search the word speedo on this forum and on the general TVR forum you will find
quite a few threads. Sensor failure appears to be the most common cause of speedo problems.
The gapping of the sensor to the toothed wheel is fairly critical. Clean your sensor and wheel and re-set the gap to eight thou' using a feeler gauge and see if this makes any difference.
Check out this thread www.pistonheads.com/gassing/topic.asp?h=0&t=240993&p=1 and the ones linked to it
>> Edited by sparkythecat on Sunday 19th March 15:52
Thanks sparky,
just having looked at the bible the sensor is supplied with 12 volts from the ignition switch.
I was therefore looking for the twelve volt supply, which isn't there, so I assumed that is the reason for the failure.
I shall look at the link you suggested.
I also looked at the sensor output with an oscilloscope directly across the two sensor wires and it did give a pulsed
output albeit only a few millivolts.
Cheers and thanks again. Back to head scratching again.
Paul.
just having looked at the bible the sensor is supplied with 12 volts from the ignition switch.
I was therefore looking for the twelve volt supply, which isn't there, so I assumed that is the reason for the failure.
I shall look at the link you suggested.
I also looked at the sensor output with an oscilloscope directly across the two sensor wires and it did give a pulsed
output albeit only a few millivolts.
Cheers and thanks again. Back to head scratching again.
Paul.
If the sensor looks old its probably gone. Consumable item and well known to go. Just make sure you connect the new one properly - I didn't double check and it didn't work for around 6 months. If it's not the sensor then you may have a long search and you'll have a spare. Lots of headscratching, earth cleaning and dash out (fooking nightmare in the Griff) and it was the wire come out of the connector on the plug - D'oh very loudly, and cost me £200 for a dealer to find, double D'oh!!!!!!!!!!!!
FFG
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