A few days ago, my car acting crazy when I turned it over. The car started but immediately started revving to about 2k RPM and down to 1k over and over (really weird!). An ESP error code popped up on the screen. It would not respond on any pedal acceleration and would just continue with a wave of revving up/down. Only after turning the car off and on again a few times did it stop doing this and the car started up and ran normal. This has happened intermittently several times since. I was able to pull a P0120 Code.

P0120
Generic - Throttle/Pedal Position Sensor/Switch A Circuit
Malfunction
Merc Specific - Throttle Potentiometer Actuator Actual value, EA/CC/ISC Actuator

I believe the TPS would be ruled out because when this error occurs, the car will start and run just fine after a few tries. I'd think with a bad TPS it wouldn't run normally at all.

I'm thinking its the battery. I'm quite sure its the original battery from a late 2002 purchase (9 years old!). However, according to the DYNO voltage readings it doesn't appear to be bad.
Off - 12.3V
On 13.8V-14.4V
I believe the lowest I got on crank was 10.8, however, it changes fast so its hard to tell. Generally it seems it doesn't dip below 11 the few times I tried this while also getting this error. It hasn't dipped to the 9.6V dead battery mark.

Does reading the DYNO voltage during crank give a true load test (consider accuracy of DYNO readings/brief crank duration/etc)?

Any thoughts out there besides a bad battery?
Any input is greatly appreciated!

BTW, Apparently...
Battery voltage = 12.7 volts at 100% charge, 12.24 volts at 50% charge, and 11.89 volts at 0% charge measured across the battery with everything off. Alternator voltage is measured across the battery with the engine running and should be minimum 13.5 volts.

 

Well the easy way out is to replace the batteries or find someone nearby that can lend you the same exact battery to find out. I woukd agree with you that if a tps error would not have the car run normally at all, but what if the tps goes bad only at start up, only after you turn it on and off a few times it "settles" down. I know its far fetched, not impossible though..

 

Waiting till the battery fails is a bad strategy as you should already be aware from the many threads of weirdness that occur at the point of failure and just before.
Additionally, when the battery is completely failed it tends to short, doesn't charge,
acts like a giant resistor, and causes the alternator to fail.
Can't think of how many times I've read in this forum of alternator failures at the time of battery meltdown.
Save yourself the aggravation and just get a new battery in advance.

Somewhere you can find some stuff I posted from the service DVD
about the TPS. I think it was in the sprint booster thread.
It's very touchy about the voltages the documents explain what causes the
errors.

 

Yeah, I agree on the stupidity of waiting out a failed battery...

I suppose my reluctancy to having already replaced battery is just to see how many damn years i can squeeze out of it... kinda like how many miles Kramer tries to get out of the test drive in http://en.wikipedia.org/wiki/The_Dealership

I'll try to get a replacement via Roadside Assistance (even though I apparently fail eligibility under their new terms )

 

I don't think I've ever gotten more than 6 years out of any car battery. Change that sucker already.

 

I got 10yrs out of my last battery. Of course it was an Interstate battery that cost twice as much as the autozone special one.

 

I changed the battery Friday morning and as expected I haven't had the problem since (other than once briefly which I chalk up to having not run the engine long enough to charge the battery the max capacity).

Hopefully this will steer anyone towards replacing the battery should they have the same peculiar behavior/problem.

 

Good new! - These cars like enough power. Reminds me - My OEM battery is approaching 8 years old & still fine. Can't go much longer.

 

My car's battery is approaching 7 years, which seems like a record for any car battery that I have had in the hot Nevada climate.

Is it cheaper to have roadside assistance do the battery, or can I save by going to my dealer for a replacement? I don't think the wholesale online dealers will ship a car battery.

 

You're right, they won't ship them. I was under the impression that you will save money by getting roadside assistance to do it as long as you qualify for it now. Mine is 6 years old, seems weak sometimes.

 

I agree with Matt - I'm pretty sure Roadside is cheaper, plus they put it in for you and remove the old. You don't even have to ruin those girly white gloves in the trunk.

 

Seems I have missed this. What are the new terms?
I used the roadsie twice in the last 6 months on my 2003 with no issues.

 

The problem popped up again today with the new battery.

At this point, I'm not sure where to start other than checking the voltage pre-start for a while to make sure something isn't draining my battery or the battery isn't otherwise being sufficiently charged.

 

Find those pdfs I mentioned.
They give you pins on the rear sam to measure the voltage from the
TPS. It's a hall effect sensor blahblah. Time to find the pdf's I posted in the
sprint booster thread.
You might need a new TPS.

 

https://mbworld.org/forums/attachmen...ccelerator.pdf

https://mbworld.org/forums/attachmen...0error2-1-.pdf

 

Unfortunately the problem persists quite irregularly. Its getting to the point where I really can't avoid it much longer.

Glyn, thanks for the links. Unfortunately I'm an ignoramus when it comes to diagnosing electronics (I own a multimeter but have yet to use it) so am not quite sure where to go with these documents. I suppose these should help in some way
https://mbworld.org/forums/3518410-post25.html
https://mbworld.org/forums/3519563-post29.html


On a side note, is an Accelerator Pedal Sensor (see Glyn's links above) the same as a Throttle Position Sensor (TPS)? I'm assuming so.

 

Put leads in your ears, test for resistance.
If less than 100 ohms you misplaced your brain. he he

 

...nerd

In the meantime i'm thinking i should maybe just replace the TPS since i don't know what heck to do with a multimeter, reading voltage, etc. Sucks that we can't just buy the sensor itself seperate from the assembly

 

Well I haven't been able to source the accelerator sensor unit itself, so in order to save a few bucks I'm considering buying a used pedal assembly.

The pedal assembly part number for my 2003 C230 is 203 300 09 04.

I've been able to find used used assemblies in the U.K. (shipped for about $82) of:

• 203 300 07 04
• 203 300 05 04

Does anybody know if these will work in my car? Perhaps if the assembly itself is different, I could at least take the sensor out and install it in my assembly. I just can't imagine any deviation in the sensor unit itself.

As a last resort, parts.com sells a new pedal assembly for $174 plus s/h.

Thanks for any insight ya'll may have!

 

Where are you? There are left hand drive & right hand drive assemblies. UK assemblies will be RHD.

 

I'm in the states, LHD. I considered this but was hoping the design (or at least the sensor) would be indifferent to RHD/LHD considerations.

If you reference the accelerator .pdf you posted above, it shows the LHD US sensor is on the right side of the assembly.

Here are pictures of the RHD assembly with the sensor also on the right side.

 

I've never compared them but they used to have different part numbers. The hall sensor is the same so you can always just change that over if there is an issue with mounting points. It's dumb that we have to buy the whole pedal assembly. Some sensors are glued in place.

 

I just wish I could make sense of this https://mbworld.org/forums/3534191-post13.html
I can tell this is great information and would probably be the fix but the language barrier and my own limitations make it so darn challenging.

 

Yes - Gus knows what he is doing & is a good guy. There is no magic here. He is just repairing/recalibrating the hall sensor. For the effort involved I would rather buy a new one thanks. The time involved may only be cheaper if you are unemployed.

 

Having the same issue with my '04... Any resolutions?