Rover SD1 Forum - Snippet #1 - Tracing Speed Transducer Faults
Here are some diagnostic ideas:
These are just general procedures to test the system, as simply replacing things randomly may not get to the actual problem.
If both Speedometer and Trip Computer are affected the fault is most likely with the incoming transducer signal, but to be sure that neither instrument is dragging the signal down, one might disconnect the signal input to each instrument and the Cruise Control ECU (if fitted) in turn and see if the other starts to function. (mod A.Foden)
If the fault remains then first check the wiring and connectors, particularly the one that joins at the lower front of the bellhousing as it is very exposed. The other connector at the transducer is also vulnerable to dirt/heat/flexing damage.
Finally the wiring where it enters the transducer can snap due to work hardening or flexing. It can also be mended by, removing the transducer to the workshop, digging out the epoxy, resoldering the wires and apply lots of new epoxy to build up a mountain of the stuff where the wires exit.
A Major Review of Rover SD1 V8 Electronic Ignition System
Description & Analysis Here:
Components & Testing Here
As for the output signal, bear in mind there are three connections
1--- Earth via the body of the tranducer.
2--- 12 volts in (white)
3--- Pulsed signal out (red/black changing to black/red).
See item 356 on the cct diagram here:
The white wire is 12 volts continuous from the ign switch and is (strangely) unfused, so it could have burned out with a short cct to the earth but should read a steady 12 volts with ign on.
The output wire will not read a full 12 volts because it has a pulsed output, never the less a multimeter will detect a varying output signal in my direct experience of about 2 volts between the output wire and the body when the 12 volts is on and the transducer is spun by hand depending upon speed of rotation. Not easy when under the car but the job can be tested on the work bench with a battery and meter.
No detectable signal probably means the transducer is toast.
Finally the fibre gears that drive the transducer may be stripped.
For multimeter skills go here: or just google the phrese - "using multimeter".
Please feel free to contact me and advise of any errors and omissions.
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