Abs unit
 

Hi all i have noticed a clicking noise when i turn ignition on but engine not running it lasts a few seconds then goes off its only done this on the odd occasion is it anything to worry about ? Coud it be ABS UNIT ?

I doubt it's the ABS unit, but just to confirm depress the brake pedal, if you can feel a slight pulsing then it's the ABS unit.

The clicking noise you're stating is probably a relay of some sort, most likely the fuel pump relay. The system pre-pressurises (primes) the fuel system to ensure that the injectors have an adequate fuel supply when you crank the engine over.

Could well be the ABS modulator unit cycling through its self-check Jim. If you start the car and drive off straightaway and touch the brakes lightly, you should feel a definite pulse after somewhere between 8-30 seconds - that's the end of the self-test.

Normally you won't hear or feel anything, just sometimes because of how you've parked or last used the brakes or whatever you'll hear it.

Keep your eye on things in case it's not the ABS unit self checking - it could also be the glow plug relay clicking on and off as you haven't started it.

I seriously doubt it's anything to do with the petrol injection system - Jims is diseasel! :tounge_smile:

Erm Okay! I’ll go back to hiding away in the corner... :mouth_closed:

Thanks Dave. I have noticed over the last year that VERY occasionally, within the first mile or so of travel, there is a VERY faint ABS type pulse through the brake pedal when applying the brakes very lightly then no more throughout that journey. Then it may not happen again for several months.
No other issues with the brakes. Your comments please?

I would say dirty sensors on the front wheels Ian. You'll need to remove the brake discs to see the sensor tips, probably covered in fine dust/metal particles, clean it off and see if the problem happens again. Also check the reluctors rings are clean.

If not then it's all good, if it does, suspect one of the sensors is on its way out. You may even be able to feel which wheel is doing it most but if they are both furred up on the front, the whole front might give you feedback through the steering wheel.

At least the sensors aren't expensive now! :thumbs_up:

Thanks Dave. That makes sense. I just wondered whether it was a warning that the ABS monitor etc. may be developing a fault.
FNS sensor is probably original. It and the reluctor haven’t had any attention since 2015 when I had an ABS warning, eventually traced to the FOS sensor which I renewed then.
FOS reluctor ring was gently cleaned last year together with the sensor when I renewed the brake back plate. The was quite a build up of scale etc. on the reluctor ring but I didn’t go mad at it in fear of cracking it or knocking a tooth off.

The teeth on the reluctor rings aren't as fragile as Shane McGowans teeth. :nah: :tounge_smile:

In case the name doesn't ring any bells, he's the lead singer of The Pogues, the one with very few teeth left! :thumbs_up:

If you have the OE spec reluctor rings, you'll find they are machined from a single piece of steel so the teeth are very solid. Some aftermarket reluctor rings (usually fited as a result of a front hub/bearing change) are pressed steel so are a little more fragile but still stand up well to brutality :

https://i.postimg.cc/0Q2csKkb/IMG-20...-144235720.jpg

https://i.postimg.cc/5NZ7Ct3R/IMG-20...-145023943.jpg

Aftermarket ^^^^^ 96 tooth reluctor ring, about 3 years old that came with the new hub/bearing assemblies. Note the two 2' tyre levers - in conjunction with an M6 x 60 set-screw through the hole (as a jacking off screw) where the brake disc securing pin/wheel locating pin lives to jack off the ring then finally levered off with the two tyre levers ~120 degrees apart each way from the jacking off screw.

Compare to a 22-23 year old 940 later 48 tooth ring recovered, derusted, sandblasted then oil blacked prior to fitting :

https://i.postimg.cc/W1g96PYb/IMG-20...-145408256.jpg

https://i.postimg.cc/d3gBrW8y/IMG-20...-145621450.jpg

First pic was to find the "right" position, although circular inside, various things can make them go ever so slightly out of round so sitting the ring on the hub and rotating it until it almost falls on or at least slides on a little by itself makes life a lot easier and the ring less likely to crack when fitted.
Removing the ring with a finger pointing to a particular wheel stud then a coating on the mating face of the ring with Threadlock (or Bearing Fit, latter for preference, either will do as both are similar) then refitted in the same "right" place and then "persuaded" all the way on by tapping round the inner shoulder round the mating face with a hammer to get it even all the way round and fully home.

As you can see, they will take punishment! In case you do need a new sensor :

https://www.ebay.co.uk/itm/ABS-Senso...1/263202894244

Had to renew the O/S/F one on mine as it started giving spurious faults (i already had a fault condition due to the mismatch of the front rings with the replacement axle) that were obvious because they showed up when they shouldn't have done. THe old one came out in two (or more!) pieces!

https://i.postimg.cc/NMRV4CjN/IMG_20..._174056668.jpg

Last ones i did on my last 740 needed a cocktail of blowlamp, drill, die grinder and various other torture instruments before they came out! :eek:

Very helpful Dave, should the need ever arise I will refer back to this.
When I needed to renew the FOS sensor I had to destroy it. It came out in several pieces. The replacement was a Bosch ( 0265001231 ) obtained through my local Bosch agent, rather than my Volvo dealership. £54.58. For items such as that, ( eg lambda sensor, ) if I can find a Bosch part number I usually check with both the Volvo and Bosch dealers.
For the record, whilst tracing the fault I noted the resistance of the “good” sensor in the FNS as 1,080 ohms. The resistance of the new Bosch sensor was 1,093 ohms. I believe that the spec. 900 ohms to (not sure).