SAM SKELTON
Skelton’s steering down a blind alley with his Daimler. Can you help?
I’M GOING to start this update with an acknowledgement that some readers will have seen something very similar in our sister title Classic Jaguar, which I also edit. But I am not sorry. I have been mulling over this issue for the best part of six months and have failed to find a solution – so I’m turning to every Jaguar enthusiast I can in the hope that someone has the answer.
Jaguar and Daimler X300s have a speed sensitive power steering system that uses ZF Servotronic components. There is an electronic receiver on the rack that varies the level of power assistance based on speed sensor inputs. This is fed by a relay-shaped ECU which lives behind the trim in the nearside front footwell. From there it follows the loom to behind the nearside headlamp, crosses the car on the engine loom (on RHD models), and is then fed into the rack near to where the column connects. The theory is, the higher your speed, the lower the assistance.
The main component here is the ECU in the footwell. Outputs from the ECU run down 2 wires to the rack, one should read 9V at idle and one should read 2V at idle. As you accelerate, the one reading 9V should rise in voltage, and the one reading 2V should drop. The bigger the difference in the voltages, the heavier the steering weight. In my Daimler, regardless of the speed, one wire reads 14V and the other 0V. It’s always on minimum assist, whether at a standstill or at 70mph the readings remain the same. I’ve tested this at the ECU and at the rack, the wiring loom doesn’t affect it with identical readings at both ends. The rack is getting the voltages that the ECU is giving it.
Logic therefore says the ECU has to be the faulty component. So let’s have a look. The ECU outputs consist of these two wires and an earth. There are two inputs; a live fused connection from the rear fuseboxes, and an input from the speed sensor in the instrument binnacle.
The speed sensor works as intended given that the automatic locking engages only as you move away. Moreover, it transmits its rea
