Hello all, I am new to the Mercedes-Benz world as owner and site. I have had my 03' S500 for almost 2 years now and she has been sitting for a couple of months. I am mechanically inclined for most part and tend to work on all my vehicles. She is currently in limp mode and sometimes it will fire and sometimes it won't. Most of time it will only fire with the push button if it cranks at all. When it runs it runs beautifully but only in 2nd gear. I have done some research and hooked up my scanner to get main code for TPS. I was wondering if this has been discovered by anyone else whom has repaired their own. I got a new throttle body since it comes with the sensor. Could this also be a MAF, crank position, or cam sensor as well? As I was looking into getting to the TPS, I have noticed that my MAF sensor back on inner housing was hanging off so I assume I will be ordering one as well. Any help with if I am on track and best way to get to TPS would be appreciated. I absolutely love this car but she is bringing me some unneeded pain right now. Thanks in advance.

 

Is your transmission in C or S mode ? The switch on the shifter puts the car in second in C mode . In S mode it should start off in first from a complete stop.

is the limp mode all the time or just some of the time? is the car not shifting out of second even as you exceeded 60-80mph? If its in lump mode you'll need to keep it floored for a while to get up to that speed

my initial suspicion is a bad accelerator pedal and a bad conductor plate on the transmission. Check your tcu in the engine compartment for fluid leakage , there is an electrical connector on the transmission that conmmonly fails and allows fluid to leak into the tcu

yes crank and cam sensors are also common failure items . As they are cheap I would change them to rule them out

if your maf was hanging off yes that's a problem , the intake system must be sealed for the car to get correct readings of intake air



Lastly you said only sometimes it will crank ? If it won't even crank some times , that could be a problem with the theft components (key , shifter, eis and ecu ) which must be replaced as

 

Ok these things I will check in to. It stays in second gear. Most of the display stopped working as well. Speedometer tach etc. The cranking issue is it will make a effort to at times and stop short, make a clicking sound like a dead battery, or start. Sometimes I can get it to and others I can not. I have the TPS and throttle body to install just never worked on these so want to make sure I don't remove any unnecessary items. Thanks for your input I will definitely check into these as well.

 

With that additional detail it sounds like a weak (but not dead ) battery that can't take the load

How old is the battery ? Might be time for a new one

 

The error codes may be real or may well be caused by low voltage/amperage. The battery must be good and must be fully charged.

The Mass Air Flow (MAF) sensor must be correctly installed, with good electrical connections and non-leaking air connections.

I suggest that the first effort should be charging the battery fully. If you then get the engine running well, write down (or photograph) all of the codes that you can get. If you can, then clear the codes and try driving the car.

Open the right front Signal Acquisition Module (SAM), which is located under the right rear corner of the hood (bonnet). Remember that right/left are always defined as if you were seated in the driver's seat, so that when you are standing in front of the open hood, the right SAM is on your left. Carefully and closely examine each of the wire harnesses and see if one of them shows traces of oil. If so, this is the Transmission Control Module (TCM) harness, and the oil is transmission fluid (ATF) that is wicking thru the harness plug on the transmission and up into the TCM. Wriggle the harness up and out, pulling the TCM (a small black plastic box on the end of the harness) out of the SAM. Open it, and use a can of spray brake and parts cleaner to completely remove all traces of ATF.

 

And if there's any transmission fluid you need to clean it and then replace the electrical connector responsible for the leak , otherwise more fluid will get in

 

Could very well be the throttle pedal. In the pedal, there are 2 potentiometer. One to feed the ECU, and another to feed the TCU. If both the computers doesn't get the same data. The computers will go haywire and throw it into limp mode.

BTW: when you shift. from P to R to N to D. Is there an display? My shifter module just failed a few weeks ago, one of the infrared detectors failed. Also stuck in limp mode.