Speedo - help please.....
Discussion
I have a 1993 Chimaera 4.0 and my speedo has suddenly stopped working (speedo and mileometer). Put in gagage working - got out of garage week later not working. Nice. Car runs fine though.
No sign of speedo problems (jumpyness or whatever) previously.
Questions :
1. is this more likely to be the clock or the cable or the sender thingy (if there is one)?
2. does the cable go to gearbox or diff or what ?
3. what's the best order to check these bits in ?
4. could this be connected with using a trickle charger ? (probably not but was just thinking of a fuse thing or something - you never know with TVR's)
5. approx cost of fix depending what it is ?
Thanks guys
Dave
No sign of speedo problems (jumpyness or whatever) previously.
Questions :
1. is this more likely to be the clock or the cable or the sender thingy (if there is one)?
2. does the cable go to gearbox or diff or what ?
3. what's the best order to check these bits in ?
4. could this be connected with using a trickle charger ? (probably not but was just thinking of a fuse thing or something - you never know with TVR's)
5. approx cost of fix depending what it is ?
Thanks guys
Dave
quote:
Is it at 9999, 19999 or 29999? See other threads on this matter...should just start up again. One bloke reversed his car around in a circle for a few minutes which did the trick!
Yes but usually the needle moves when this happens. Could be the sensor could be the clock and there is no cable as this is completely electronic. Difficult to see what is wrong unlessyou have access to an oscilloscope to see if there is a signal coming from the sensor. Could try cleaning the sensor and looking for bad connections.
Steve
www.tvrbooks.co.uk
It's a clue but I wouldn't rely on it. Yes there is a speedo input to the ECU but the decision making process for the idle speed is complex and its behaviour may or may not be changed due to a sensor problem.
It all goes back to the Heath maxim that says all sensor tests will only tell you if a unit fails that test but not that it is good. Apply this to the ECU and yes that could indicate that the ECU is receiving something but not that the sensor is working correctly for the speedo. Been down this path so many times now that I take nothing for granted and assume nothing.
If you want to check that the sensor is correct, put a scope on it and make sure it is switching at the correct voltages everytime a tooth comes near it. It is possible that it is intermittent which indicates to the ECU that everything if fine but is insufficient to drive the speedo.
You need a scope as a multimeter may not register the changes or its impedance may affect the reading and so on. SO again it is a question of is the lack of a reading on a multimeter a fault or not?
BTW the sensors and speedos are matched units and are calibrated for the appropriate number of teeth that is used on the car. And yes this has varied!
Steve
It all goes back to the Heath maxim that says all sensor tests will only tell you if a unit fails that test but not that it is good. Apply this to the ECU and yes that could indicate that the ECU is receiving something but not that the sensor is working correctly for the speedo. Been down this path so many times now that I take nothing for granted and assume nothing.
If you want to check that the sensor is correct, put a scope on it and make sure it is switching at the correct voltages everytime a tooth comes near it. It is possible that it is intermittent which indicates to the ECU that everything if fine but is insufficient to drive the speedo.
You need a scope as a multimeter may not register the changes or its impedance may affect the reading and so on. SO again it is a question of is the lack of a reading on a multimeter a fault or not?
BTW the sensors and speedos are matched units and are calibrated for the appropriate number of teeth that is used on the car. And yes this has varied!
Steve
Thanks guys
And there was me hoping it may be a wire that's come off or something now I'm looking at £150 sensors and ECU failures etc !! Blimey.
Actually, is there a chance that the ECU has taken a knock or something. If the ECU is the collection of fuses and boxes down by the battery in the footwell this could be so as I recently had the battery out to charge it. Mind you, the speedo worked immediately afterwards so maybe not ?
What I didn't say is that the diff is whining and needing replacement soon (not due to potential imminent failure - more due to irritation of the noise spoiling the experience) so this seems a little co-incidental ?
Dex
And there was me hoping it may be a wire that's come off or something now I'm looking at £150 sensors and ECU failures etc !! Blimey.
Actually, is there a chance that the ECU has taken a knock or something. If the ECU is the collection of fuses and boxes down by the battery in the footwell this could be so as I recently had the battery out to charge it. Mind you, the speedo worked immediately afterwards so maybe not ?
What I didn't say is that the diff is whining and needing replacement soon (not due to potential imminent failure - more due to irritation of the noise spoiling the experience) so this seems a little co-incidental ?
Dex
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