Clutch Position Sensor resistances
 

My CPS started failing again after I fixed it in 2013 – see this post – https://www.volvoforums.org.uk/showthread.php?t=190739
The cruise control was operating intermittently and when I performed the following check it confirmed it was the resistance of the CPS in the extended position that was likely to be the problem
With the ignition on (but car not running) – push the clutch down and then press the cruise button. “cruise” is then displayed on the DIM – then allow the clutch back up and if the “cruise” goes out it’s likely the CPS resistance when extended is faulty (too high).
When I first fixed my CPS in 2013 I put it inside a plastic bag but regardless of that it had brake fluid over a lot of it (including inside the bag) so “bagging” it didn’t work very well tho’ I took care to only have one hole at the bottom etc. There was fluid on the carbon track and the contact fingers inside the CPS. The brake fluid leak comes from the clutch rod above the CPS and looks (to me) like a “scraper ring” type leak. It was interesting to see that the fluid doesn’t appear to change the resistance much (it was the same 3.2kohm resistance after I cleaned the fluid off with meths) – I’m told carbon tracks drift high anyway and maybe the brake fluid speeds the drift or makes it worse.
The resistance was 3.2kohms extended & 530 Ohms retracted – when I fixed the CPS before I had set the extended resistance to around 3kohms using a 5.6kohm resistor in parallel – see post above.
So it has drifted up to 3.2kohms since 2013 which has taken it outside the range that will work.
I removed the previous 5.6kohm resistor I had fitted in parallel and changed it for a 4.3kohm one (it was a 0.6w one from maplins for 10p !) to give me a measured extended resistance of 2.7kohm (to allow for some future drift) and a retracted resistance of 530 ohms. Put it back in the car and it has been fine for the last 3 months now.
So the key info is that the CPS needs an extended resistance of 3 kohms max (but 2.7 kohms is fine to allow for some future drift) and a retracted resistance of up to 530 ohms is ok. I think a new one is around 200 ohms.
Hoping that helps people who like fixing things – this really is a case of a 10p fix instead of a £40 component being replaced.
Final note – as my original “bagging” of the CPS didn’t work well I still put it in a bag but also put some absorbent material on top of the CPS (where the leak drips) in the hope that the leakage will retained by the material and I can check it and change it when it’s saturated.
Photos showing latest resistor soldered in, plastic bag & material attached.

I didn't bag my first replacement because there was no sign of the alleged drip.
It lasted less than a year.
The second has been in there bagged since 2009. There was evidence of a drip in fact the slider track was complete mush.
I see a rheostat on your dash in the future :)

Please be aware as to how corrosive brake fluid is; if it’s dripping inside the cabin somewhere, it’s going to end up underneath insulation etc and then it WILL eat whatever metal it finds soon enough. Is there not an argument for changing the clutch master cylinder?

CPS resistance
 

I intend go to my local scrap yard to get a replacement CPS for my 2003 V70
and bring my DVM. What resistances ranges will indicate a good one, extended and retracted ?

Jude

Jude,

The info I think your looking for is in the 1st post -

The key info is that the CPS needs an extended resistance of 3 kohms max (but 2.7 kohms is fine to allow for some future drift) and a retracted resistance of up to 530 ohms is ok. I think a new one is around 200 ohms.

I.e. extended you want 2.7 to 3.0 Kohms
retracted you want 200 to 500 ohms

cheers
Jools

The bagged 2009 replacement has now lasted twice as long as the original and counting :)

The CPS I removed from a V70 in the scrapyard today had the following resistances -

Retracted- 230 ohms
Extended - 3.1K ohms
The cruise control now works and I was surprised that the DIM warning- Engine Service Required- has now disappeared. I paid £5
The faulty one I removed from my V70 had the following resistances

Retracted- 385 ohms
Extended - 5.6K ohms

Jude

Jude,

my only comment would be that mine stopped working when it had reached 3.2kOhms - so you may not have long to wait before yours drifts from 3.1k to 3.2 k !

If it does simply put a resistor in parallel as per the 1st post in the thread.

Jools

This is of great interest as I'm 99% sure my CPS is dead. All of the signs are there, ie cruise engaging when the car is started with the clutch down then disengaging as it's raised, same symptoms with the engine service required message.

A couple of things I'd like to ask before I pull the sensor and measure the resistances through the sensor's travel:

1: How does one decide on what rating of resistor to use?

2. Looking at the image in the first post (Thanks for uploading them!) it appears as though the resistor is soldered onto the spades that the pug slides into? Does this not interfere with actually plugging it in and connecting it?

TIA

I have an auto that shows "CPS failure" or similar is this legit?