My CX Turbo S2 has a period VDO 'Tempostat' cruise control which was not working when I got the car. It is the electric servo, cable type rather than the earlier vacuum type.
There is quite a bit of info on troubleshooting and repairing these as they were factory fitted on MB, Porsche, BMW etc of the era. I have followed the diagnostic and repair instructions and still can't get it to do anything at all when installed in the car...
The last questionable component is the speed sensor - at the moment the cruise electronic unit is plugged into the original inductive sensor fitted in-line on the speedo cable (used for the original 'on board computer). When I tested the sensor resistance from the control unit plug I got nothing, and I then got no continuity on one of the wires. Seeing no obvious breaks in the wire, I unwrapped the loom at the control unit end and found a small zener diode soldered in series...
In the limited info I got with the car there is mention of 'remove VDO sensor'... from the '90s.
There is very little info I can find about the sensors used with this system on other makes. It appears that the MB sensor is a hall effect 3 wire unit. There is no evidence that the plug for the cruise control on mine has been changed or was once 3 wires. The terminal is identical to the Citroen trip computer one, and there is a short splitter loom with the same plugs which allows both the trip computer and cruise to connect to the 'factory' sensor.
The MB hall sensor is inbuilt with the speedo. The only other VDO sensor I could find was from a Porsche, which is inline and inductive, but for the earlier vacuum driven units.
So, my question is whether anyone has knowledge of this system, and would the control unit be fussy about the speed signal, ie an inductive sine wave or a hall square wave?
If I can assume, from what looks to be the original wiring, the cruise should work with an inductive sensor, what would the zener diode be for?
Cheers, Steve
There is quite a bit of info on troubleshooting and repairing these as they were factory fitted on MB, Porsche, BMW etc of the era. I have followed the diagnostic and repair instructions and still can't get it to do anything at all when installed in the car...
The last questionable component is the speed sensor - at the moment the cruise electronic unit is plugged into the original inductive sensor fitted in-line on the speedo cable (used for the original 'on board computer). When I tested the sensor resistance from the control unit plug I got nothing, and I then got no continuity on one of the wires. Seeing no obvious breaks in the wire, I unwrapped the loom at the control unit end and found a small zener diode soldered in series...
In the limited info I got with the car there is mention of 'remove VDO sensor'... from the '90s.
There is very little info I can find about the sensors used with this system on other makes. It appears that the MB sensor is a hall effect 3 wire unit. There is no evidence that the plug for the cruise control on mine has been changed or was once 3 wires. The terminal is identical to the Citroen trip computer one, and there is a short splitter loom with the same plugs which allows both the trip computer and cruise to connect to the 'factory' sensor.
The MB hall sensor is inbuilt with the speedo. The only other VDO sensor I could find was from a Porsche, which is inline and inductive, but for the earlier vacuum driven units.
So, my question is whether anyone has knowledge of this system, and would the control unit be fussy about the speed signal, ie an inductive sine wave or a hall square wave?
If I can assume, from what looks to be the original wiring, the cruise should work with an inductive sensor, what would the zener diode be for?
Cheers, Steve
