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On my 2001 winter pack 147 it has a Clutch Pedal Switch as well as the Brake Pedal Switch.

I know the brake pedal switch is for the brake lights as well as something else but I don’t know what the clutch pedal switch does.

I have Cruise Control but I think the brake pedal switch cancels that; but I don’t know what the clutch pedal switch does…
Any ideas?
Ta!
 

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it's also for the cruise control, in addition to the functions of the ABS system (abs, traction control, VDS etc) and I believe also to control idle rpm
 

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The switch on the clutch pedal 'informs' the ABS control unit (ECU) whether the clutch is engaged or has been disengaged, so that the ECU 'knows' when to allow criuse control to function and when it must be disengaged. If this didn't happen then when the clutch disengages (i.e. the pedal is depressed) the cruise control would remain engaged, and the ECU would keep engine RPM unchanged at whatever the cruise RPM happened to be.

Also, if the cruise control did not disengage, and the road speed were decreasing (because the engine is not 'connected' to the drive wheels because the clutch is disengaged), the ECU would attempt to maintain the selected cruise speed by increasing engine RPM. Of course this wouldn't work, the road speed would continue to diminish, and so very likely the ECU would detect a fault and disengage cruise control (given the disparities between selected cruise speed, engine rpm and the actual decreasing road speed). This might not happen instantly...

The brake pedal switch does brake lights, and the "something else" is to inform the ABS ECU unit that the brakes have been applied, so the ECU 'knows' to disengage cruise control.

Regards,
John.
 

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As I recently found when I accidentally disabled the switch, and found I had to relearn the clutch to avoid jerky changes, it also triggers a gear change assist function which helps to match engine speed to the next gear selected. This was on the 20 valve diesel, I don’t know if any of the other engines do it
 

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I was talking about the switch on the clutch pedal ;)
My misreading...

My understanding, FWIW:

The ABS ECU always 'knows' whether the clutch switch is 'on' or 'off', but AFAIK it only uses this 'knowledge' to allow / disallow cruise control function. This data isn't really needed to control ABS, VDC, or ASR (I could be wrong, but I can't see why the ECU would need to referance the clutch for these purposes). As I understand it, the 'ABS' ECU controls ABS, VDC, ASR according to inputs related to relative wheel rpms, road speed, and yaw sensor signals. Why would the ECU need to 'care' what the clutch is doing?

Also, I doubt that the ECU does anything to the idle RPM based on the signal from the clutch switch. The ECU has no way to 'know' what it is that might be causing the idle RPM to try and change from programmed RPM, it just reacts to correct any momentary rises / falls.

Regards,
John.
 

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My misreading...

My understanding, FWIW:

The ABS ECU always 'knows' whether the clutch switch is 'on' or 'off', but AFAIK it only uses this 'knowledge' to allow / disallow cruise control function. This data isn't really needed to control ABS, VDC, or ASR (I could be wrong, but I can't see why the ECU would need to referance the clutch for these purposes). As I understand it, the 'ABS' ECU controls ABS, VDC, ASR according to inputs related to relative wheel rpms, road speed, and yaw sensor signals. Why would the ECU need to 'care' what the clutch is doing?

Also, I doubt that the ECU does anything to the idle RPM based on the signal from the clutch switch. The ECU has no way to 'know' what it is that might be causing the idle RPM to try and change from programmed RPM, it just reacts to correct any momentary rises / falls.

Regards,
John.
From elearn, for what it's worth ;)
<snip>
Control of the idle speed
The control unit recognizes the idle condition from the accelerator pedal being in the 'released' position.
The control unit controls the position of the motorized throttle to control the idle speed according to the consumers switched on and the brake - clutch pedal signals.
Idling speed when warm is 840 ± 50 rpm.
 

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Might not be obvious on alfas, but plenty of asian cars I worked on had different idle speeds with clutch depressed or released.
 

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Some searching finds that apparently some cars are set up so that;

With engine idling and car stationary, when the clutch pedal is depressed the ECU increases the 'idle' speed to some degree, to assist with taking off from rest. I've never noticed this ever occurring with my TS 147, nor did it happen earlier today when I was on the lookout for it. Nor have I ever noticed it with any other car (that I have driven...).

In the name of curiosity, I also later reached under the dash and disconnected the wires from the clutch switch. The car drives quite normally with the switch disabled, no check lights and the cruise control functions as it should. That is, until the clutch is depressed, at which moment the engine RPM leap by about 500 RPM, the ECU obviously detects a problem, and disengages the cruise control. I still think this is the primary purpose of the clutch switch, i.e. when operating cruise control, to avoid the RPM momentarily jumping when the clutch is disengaged.

Regards,
John.
 

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From the above eLearn excerpt:
"The control unit recognizes the idle condition from the accelerator pedal being in the 'released' position."

My understanding is somewhat different, possibly pedantically so:

The ECU can't "recognise the idle condition" (i.e. 'know' what the idle RPM actually is) by the signal from the accelerator pedal potentiometer. The pedal signal being "released" only tells the ECU that the demand is for the RPM to be at or near to specified idle speed (i.e. 840 ± 50 rpm), and that this is the RPM which the ECU should be aiming for. The ECU "recognises" or 'knows' what the RPM actually is from the crank position sensor signal (including RPM at idle).

"The control unit controls the position of the motorized throttle to control the idle speed according to the consumers switched on and the brake - clutch pedal signals."

I'm still less than convinced that this is actually true (I don't take it for granted that every detail I ever encounter in a workshop 'manual' is always Gospel...).

Lets assume that the engine ECU does not act to increase idle speed in order to assist in driving away from rest, as it doesn't appear to do so with my 147...

Given this assumption, why would it be that the engine ECU would need to 'know' the position of the clutch pedal to maintain a specifc idle speed? I don't think it does, and probably ignores this input for this purpose, or maybe the ABS ECU may not share this information with the engine ECU...? (which of course it could if there were a reason to do so...).

The engine ECU also doesn't need to know which "consumers" are creating parasitic load or how much, only that the resulting idle speed is moving out of spec. All the ECU would need to 'know' is that 'demand' is for idle RPM, (throttle pedal is "released"), and what the the momentary RPM actually is. From these two inputs the ECU can continuously trim idle speed as required, regardless of what other factors might be 'trying' to alter it. At least I can't see why any other inputs would be needed, it's a fairly simple feedback loop...

Regards,
John.
 

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Given this assumption, why would it be that the engine ECU would need to 'know' the position of the clutch pedal to maintain a specifc idle speed? I don't think it does, and probably ignores this input for this purpose,
It probably doesn’t need it to maintain the idle speed but may do to establish idle smoothly. There is a thread somewhere where the rpm was undershooting (almost to stall if the air con was on) when the clutch was released during over-run, but only if the speed was above 15Kph* (I think). I thought it might be that the ecu was holding the throttle further closed than the idle position during over-run to save fuel, and needed the warning from the clutch switch so it could avoid the undershoot. (Below *15Kph I thought the ecu would open the throttle to the idle position so as to be ready to idle the engine.) Unfortunately, that thread was never resolved.

*Edit: 30Kph.
 

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I know that idle speed is f.i. increased somewhat when airco compressor is engaged., also battery voltage during idle has an effect.....
 

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just for info, here are the used inputs etc on the Bosch M7.3.1 EOBD injection system as used on the 147 :
 

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