Do we have another Jaguar info error when looking at the X300 variable steering module (Servotronic) wiring diagram which states -



Pin CA32-2 Red Transducer Neg. 2v @ idle decreasing with speed

Pin CA32-4 Blue Vehicle speed B+ @ 10mph =20Hz, 20mph = 40Hz

Pin CA32-5 Slate Transducer Pos. 9v @ idle increasing with speed



Jaguars own workshop manual 10.1 Steering system description states -

“At very low speed, e.g. when parking, a low-speed signal is delivered to the PSCM (power steering control module). Correspondingly, maximum current (700to 800mA) is supplied from the PSCM so that the steering rack transducer is activated to the closed position”



“At moderate driving speeds, the speed signal is received by the PSCM and is transmitted, as a decreased proportional electrical current value, to the transducer.”



So basically, this means with maximum current applied (low speed/idle) 700/800mA is supplied to the transducer valve which results in light steering.



At speeds above this, very little current is received at the transducer valve, and we then have heavier steering.

No voltage at all at the transducer valve results in heavy steering at all times, basically the default if the servotronic module or transducer fails.

ZF info available indicates the current is at maximum value at 854mA decreasing with speed down to 15mA.



This I find contrary to the info in the wiring diagram set out above, it states the transducer voltage increases with speed, starting from 9v at idle on the slate wire.

John Herbert
1996 XJR

 

Yea , it's weird as I put a meter on it as a non rolling car back some time ago

" No voltage at all at the transducer valve results in heavy steering at all times, basically the default if the servotronic module or transducer fails."

Makes sense and will look at it more in morning

 

might be able to do some testing on a dead module as i suspect the module may be not great in my parts car.
the steering in it is great under normal driving.
but at low speeds like parking and such it is very heavy.....
car is currently not mobile so can't do too much.
(plus very busy working on my driver atm)

 

The servo amplifier is used on Volvo models from reading and an information source may be on their forums , and I think also BMW 740 ( E38 ) models

 

The transducer ( 402 ) ( servo ) on the rack should read 7.5 ohms through pins 2 ( red wire ) and 5 ( slate wire ) on the amplifier connector for the rack side ref the ZF doc page 16

That squares up your rack side if good

Your fuse is # 12 / 10 amp right heelboard fuse box

 

I have now conducted further testing of the servotronic module connected to the transducer on the work bench and with a 12.8v power supply and a PWM (Hz signal) generator to supply the required speed signals.

The readings were taken with the multimeter negative to earth and the positive to the appropriate wire to the transducer, slate to pin 2 and then red to pin 1. The transducer needs to be connected to provide the load.

The results are attached and what is very evident is that the wiring diagram info is incorrect.

Pin 2, the transducer positive does not increase, it decreases with speed,

Also supplying 12.8v to the module and with the transducer disconnected (no load) and no speed signal, voltage pin 2 was 12.19v and at pin 1 0v, not 9v and 2v.

Note there is only slight differences in the Jaguar and Volvo module outputs.

I have since fitted the Volvo module in the car and a short drive indicates it is working as designed. Assistance at idle (low speed) and lessening at speed.

I am now at a loss to know why my original Jaguar module is not working correctly.

I had previously installed a temporary fix which worked well, I installed a DC to DC converter module and set it at 7v output which I connected directly to the transducer. This worked great, giving full assistance at low speed and I considered steering was not over sensitive at speed, despite having the same level of assistance from idle to normal speeds. There is no speed variation available using this method.

John Herbert
1996 XJR

 

Very interesting. I have some further diagnosis to do on mine since the power assist struggles at idle when the car is warmed up.

Would you happen to have the part# handy for that Volvo module you picked up?

 

always good to note any part substitutes.

 

John has The Volvo # in his PDF in post # 6

" I have some further diagnosis to do on mine since the power assist struggles at idle when the car is warmed up. "

Old worn out PS fluid cavitating ( air bubbles forming on low pressure side effecting pump effort ) at the PS pump ?