C4 VTS P1644

[Cutac]

Hello
As the title says, my C4 VTS is giving me P1644 and speed limiter isn't working.
Here's a photo of the Diagbox screen, I'm a moron, don't know why I didn't take a screenshot...

[Fake Concern]

Looking at the C4Owners list of fault codes we get.........Accelerator pedal point of resistance information fault : Short circuit to positive & Vehicle speed limiter switch : Short circuit to positive

Have you tried the usual fix for this of some contact cleaner on the roller switch, roll it back and forth a few times, move the steering column up & down and in & out to clean alll the contacts?

[Cutac]

Did try cleaning, also installed that modified brake pedal switch - no luck.
Cruise control works fine.

Maybe cleaning the throttle position sensor?

[GiveMeABreak]

This will be the throttle potentiometer (accelerator) - the 'tight spot' voltage is probably higher than 4.5 or 4.7V (you have the Magneti Marelli Injection variant) and these are for the Bosch and Siemens systems - but they are almost identical issues both pointing to the accelerator.

Give the track a clean as Mr Concern suggests, but ultimately, they do wear out at some point.

[Cutac]

So there would be no repair possible?
By cleaning the track, you mean cleaning the limiter/cruise control switch or cleaning something else?
Is there any way to check voltage reading?

Also, could worn potentiometer cause this: When I press the throttle a bit(like a millimeter or two), revs raise to approximately 1100 and drop slowly, all in the course of two seconds?

[Fake Concern]

I'm pretty sure the pedal doesn't have a physical "track" it uses a magnetic system so that there is no part to wear. The position sensor is also part of the throttle body. Given what has been said above, my first suggestion is to clean all the electrical connections to the pedal and throttle body (which is easily accessed on the VTS).

[GiveMeABreak]

There are usually 2 halves to the assembly - each sending out different information, but even if you can push the pins through and remove the 2 covers of each, there is little else visible - so if proven to be faulty, it's probably better to replace it. Some electrical contact cleaner (and only this) may help.

[Cutac]

I'll just was the pedal in contacts cleaner and hope for the best.
What about the throttle body? What can be dissasembled? I've cleaned the butterfly valve, but what abot the controller of it?

[Hell Razor5543]

Make sure to use PROPER contact cleaner, and not something like WD40.

[Cutac]

Don't worry
Thanks, though

[Cutac]

Where on the throttle body is a throttle position sensor? Would like to clean that too.

[GiveMeABreak]

The actual throttle position sensor is incorporated into the accelerator pedal. The request to open the air regulating flap is no longer a direct command by cable linked to the accelerator pedal.

• The accelerator pedal sensor informs the injection ECU of the driver’s request.
• The injection ECU then commands the butterfly housing motor.
• A potentiometer incorporated in the throttle housing allows the injection computer to determine the exact position of the air regulating flap.

Item 6 is the Air Intake Throttle Valve Housing

If the power fails to the unit, there is a spring incorporated into the unit that allows sufficient air for low power. I don't think you have this fault though or you would be in 'limp home mode'.

It is also odd that your cruise control is working ok - I would expect that it the accelerator pedal sensor was at fault that this would also affect the cruise function. So I'm wondering looking at that Diagbox fault - that it could be a dirty contact as 'Fake Concern' said - on the roller switch of the cruise / limiter stalk. Get some electrical contact in there and work it through whilst spraying.

A new one can be had for £138, part number 6239RC:

https://www.ebay.co.uk/itm/Steering-Col ... 2477913631

[Cutac]

Washed the throttle pedal thoroughly and Limiter still doesn't work, but idle is much smoother and there's no more rev hang going from first to second.