Electronics - which resistor for clutch position sensor?

[Tc24]

Wondering if someone could help me with an electronics conundrum please...

I'm trying to fix my S60's clutch position sensor per the video here:

https://www.youtube.com/watch?v=PjnPWieNtM4

I've measured resistance across the sensor and it's approximately 1.1k ohms closed and 14.6k ohms open. I think the values are meant to be 200-300 ohms closed and around 3k ohms open.

I've tried to work out which size resistor to solder in parallel by using R = (R1 x R2) / (R1 + R2), treating R1 as the current when the piston is extended/contracted. Problem is, it works out to be something like a 400 ohm resistor being needed when contracted and a 3k3 when extended. I've tried with a couple of resistors I already have and it seems to back these figures up.

Question is - does a single resistor exist that would give me something close to the required values? Or is the sensor FUBARd and too far out of range to be repaired? My maths suggests the latter, but I don't understand the physics well enough to say that for sure.

Thanks in advance

[Tc24]

In fact, the more I think about this the more I think a resistor won't work in this case.

Essentially, the resistance is 5x what it should be in both cases. Adding in a resistor to my knowledge won't reduce this as a set multiplier, rather will have a greater effect on the upper end resistance (i.e. 14.6k) than the lower end.

Unless I've misunderstood, mathmatically you then have an impossible simultaneous equation where:

14600x / (14600 + x) = 3000 and 1100x / (1100 + x) = 300

If correct I suppose this changes the question to... is there a component other than a resistor that would achieve this?

[E-bmw]

Tc24 said:

If correct I suppose this changes the question to... is there a component other than a resistor that would achieve this?

What about replacing your defective clutch position sensor with a working clutch position sensor?

[Polly Grigora]

Whoever presented that video overlooked the fact that there is nothing stable about a potentiometer once it's gone out of range due to wear or whatever

The unstable out of range resistance values have been used for calculations

The calculated resistance values to bring the sensor resistances back within range are meaningless due to the fact that the unstable values used won't constantly remain the same

[Tc24]

E-bmw said:

Tc24 said:

If correct I suppose this changes the question to... is there a component other than a resistor that would achieve this?

What about replacing your defective clutch position sensor with a working clutch position sensor?

Where's the fun in that ?

I did in fact order one last night having been 80% sure it was dead. Answer below seems to confirm as much. £70 lighter for cruise control I'll rarely use....

Polly Grigora said:

Whoever presented that video overlooked the fact that there is nothing stable about a potentiometer once it's gone out of range due to wear or whatever

The unstable out of range resistance values have been used for calculations

The calculated resistance values to bring the sensor resistances back within range are meaningless due to the fact that the unstable values used won't constantly remain the same

That makes sense, thank you. Even it was linear and I could get a resistor to bring down initially, expect it'd go out of range again at some point.

Worth a look but ultimately replacement should be the answer.

[Polly Grigora]

Tc24 said:

That makes sense, thank you. Even it was linear and I could get a resistor to bring down initially, expect it'd go out of range again at some point.

Worth a look but ultimately replacement should be the answer.

Ok then

Wondering if a double pole micro-switch would work as a replacement, using 2 seperate resistors switching a high or a low expected resistance

Can't for the life of me think of a reason why the cruise control circuit would need anything other than high and low switching, surely any mid range resistance value during the travel of the clutch wouldn't be needed

[Tc24]

Polly Grigora said:

Ok then

Wondering if a double pole micro-switch would work as a replacement, using 2 seperate resistors switching a high or a low expected resistance

Can't for the life of me think of a reason why the cruise control circuit would need anything other than high and low switching, surely any mid range resistance value during the travel of the clutch wouldn't be needed

That would make sense. Having read another thread I understand the switch also controls the throttle to a point, assisting with feeding power back in post-gear change.

Doesn't seem to make any difference to real-world running however so I'm skeptical.

Agree that an on/off resistance (or standard switch) would've sufficed at design stage to turn cruise control on and off. All this throttle interference from the ECU just seems unnecessary!

[Polly Grigora]

Mmmm, not so simple then

[VanDiesel99]

beyond my knowledge, but I've been really impressed with DiagnoseDan's channel on YouTube, which was recommended to me by someone here; the way he explains electronic stuff makes it seem a lot less scary than I thought... could be especially useful if the new part isn't the answer