I have a fault code of C1285 Booster Solenoid Output,
Can anyone give me any info on what it is, where it is and what does it do please ?
I've searched on here and I can't see the info I need, I suspect it's on the brake servo unit (UK. car) but any info regarding this would be gratefully received.
Thanks

 

Hi Richard,
Although my version of XJ8 is a bit later and does not have a brake booster solenoid, I'm curious and have done a bit of reading to try and educate myself on this feature.
Here is a link that briefly explains the operational principle of the solenoid and possible generic causes of issues.
https://www.autocodes.com/c1285.html

I have downloaded the earlier schematic which I hope should be quite relevant to your year, so have a couple of initial checks you can do if you have a multi-meter.
On the off-chance you have a fuse out, firstly check the 5 amp fuse F17 of the passenger junction fuse box. If that is OK we'll move on.

The solenoid is located on the brake booster servo I think, along with a pedal travel sensor and pedal force switch.
There should be two connectors going to these items, a three way connector that goes to the pedal travel sensor and a five way connector that connects the pedal force switch along with the brake booster solenoid.
That five way connector is probably where you want to start.

Check the five way connector and pins for any obvious corrosion from water ingress.
Next check the solenoid itself for continuity using your meter on the low ohms setting. This type of solenoid probably has a very low resistance so you will be looking for a reading of somewhere around 2 to 5 ohms (doubt it would be any higher).
To measure the solenoid you are looking at pins 3 and 4 of the five way connector, the pins that would normally receive the black/white wire to pin 3 and the red/white wire to pin 4 if the connector were plugged in.

If the solenoid appears good, then the next test is to check the integrity of the other end and the wiring loom by reconnecting the five way connector to the brake booster and locating the 47 way connector to the dynamic stability control module. Undo that connector and again check for any obvious corrosion on pins and sockets.
With your meter on low ohms again , check resistance between pins 17 (red/white wire) and 31 (black/white wire)....you should have a similar low resistance measurement of the solenoid being present (plus an additional 1 or 2 ohms for the wire resistance). If the solenoid resistance is measuring particularly high, then you maybe looking at a damaged or fractured wire and you then want to measure from end to end of each of the two individual wires (Black/White then Red/White) to ascertain which may be at fault.
If solenoid is measuring present at the 47 way connector, I would probably check your earthing point serving the dynamic stability control module which is below the power distribution box (G2 ground) just in case you have an issue there.
Beyond that, I guess we would have to become wary of the dynamic stability control module itself - but I personally would rule out as much as we can prior.

 

Thank you Mark that's much appreciated.

 

on the active booster

 

Thank you, I think part of my problem is the terminology ! I am used to it being called a brake servo, at least I think it's the same item !