P0120 Pedal Position Sensor - Mercedes Benz SLK Forum

SLK R170 General Discussion SLK 200, SLK 230K, SLK 320, SLK32 AMG

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#1 Old 05-18-2019
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Thumbs down P0120 Pedal Position Sensor

Haven’t been on the forum much recently, life and a growing family have a way of doing that; but my 2001 SLK320 has been enjoying a pampered life as a weekend cruiser in the summers, and has been trouble free for years now. However, I just took it out of storage for the season today and I am having the first bit of trouble I’ve had in awhile with it….

The car had been in the garage on a battery maintainer all winter, about a couple weeks ago I unplugged the maintainer, but never got around to starting the car. So today I finally got to it, started right up and idled perfectly, so I pulled it outside and let it idle in the driveway for maybe 10 minutes. Got in to take it for a ride and immediately noticed that I had almost no throttle response, I can floor the pedal and the car will only very slowly take off from a stop – bad enough that it’s too dangerous to drive much at all around here.

I shut it off and turned it back on again and this time I got a check engine light, so I ran the code and it came back as “P0120” “Throttle/Pedal Position Sensor A Circuit”. Tried disconnecting the battery, leaving it disconnected for ~10 minutes and reconnected with no change. I’ve also tried the TPS reset procedure (holding pedal to the floor for 5 seconds with the ignition on) without any success.

Curiously, if I have the ignition in the ‘on’ position and clear the P0120 with my code reader, then immediately refresh the code reader the error code comes right back, so I figure whatever it is, is giving the ECU an obviously bad signal all the time. Seems weird that something electronic would die like this while the car is stored, but I guess anything is possible.

Research suggests there are two Throttle Position Sensors? One in the pedal and one somewhere else? Any thoughts on what to do/try next? I would like to avoid just throwing parts at it if possible….But I am also not interested in taking it to a dealer, or even an indy for this quite yet….
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#2 Old 05-18-2019
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#3 Old 05-18-2019
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Thanks - Will give that a try.
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#4 Old 05-19-2019
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Hi,

Replacement Pedal needed.

These pedals are noted for going bad with no warning, recently replaced one on my S55.

Both sensors are in the Pedal assembly.

HTH,

Cheers Dave
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#5 Old 05-19-2019
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Thanks for the responses. I tried the reset procedure again with no luck, so I removed the pedal assembly earlier tonight and figured I'd just inspect the connections and such before I went ahead and ordered a new one. Everything looked fine, so I waited maybe 20 minutes and then plugged it back in and gave the car a try - oddly, everything is working fine now.

So now I am not sure if it was just a fluke related to the car having sat for ~6 months, or whether there's actually something wrong with the pedal sensors.

I'll bolt it back in tomorrow and take it for a good drive to see if the problem returns
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#6 Old 05-20-2019
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I had much the same problem with mine. Before you not it back in though, treat the connections to a little contact grease to stop any moisture getting in and causing problems later on.



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