Reducing a 0-5v wire to output only 0-1.3v...help please

Hmm. All you need is the resistors, not the regulator.

In fact, just use a potentiometer from Radio Shack. Try a 10K pot. Wire the two outer leads to the sensor and the center lead (wiper) to the ECU. You need to cut the traction control sensor wire. I am guessing the return path is ground.

Once wired up you can dial the potentiometer so that it delivers 1.3 VDC when the input is 5 VDC. Add a dab of cement to the shaft of the potentiometer when it is set and you should be good to go, I guess.

However, why not look up a Mercedes web forum and ask what other owners have done?

Thats just the thing no one has tried to defeat the system yet everyone wants to because mercedes are perfectly balance race cars for SCCA and Auto-X in the Stock and Prepared Sedan divisions but you must use the stock ECU and the traction control kills a lot of peoples efforts. It creates a lot of understeer(car wont turn when you want it to), turns the power down in the motor, and kills your brakes cause your wheels are spinning while the rear tires are clawing through them.

So this potentiometer wouldnt it need to be set to start reducing at 1.3v because 5v would be me doing donuts in a parking lot (tested ) and 1.3v would be like me flooring it from 0 (also heavily researched ). I want to be able to completely eliminate the traction controls influence.

You need a signal isolator. ActionPak has many varieties.

They have dip switch selectors, and calibration pots to allow a wide range of inputs and outputs. You can set 5V input to equal 1.3V out, and it will be linear. They are not intended for autos, but they do have locking mounts for vibrating installations.

They can be powered from 12 VDC through 120VAC.

Everyone seems to be assuming that you need a linear divider which can be achieved with either two resistors or a potentiometer as Anonymous Hero suggested.

Just to clarify, do you need a linear divider or a voltage limiter?

The linear divider just converts the 0 to 5V to 0 to 1.3V. When the input is 2.5V, the output is 0.65V, if that is the case.

The voltage limiter just limits the voltage at a certain value. When the input is less than 1.3V, the output is equal to the input. When the input is 1.3V or more, the output is pegged at 1.3V and won't increase any further.

The two circuits are different. Which is it?

I think I was wrong in which wire i tested, I tested just one of the 8 sensors for teh traction control. The left wheel speed lol oops. It was quite fun having my left wheel go crazy with the one wheel drifts so i can sort of gain a concept for what you guys are telling me.

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Isn't modifying the sensor signals, modifying the ecu? One of those nitpicky things that will come back to bite you , if you start winning!

That being said..... why not just disable the pump? isn't this pump applying the brakes? You may need to determine the current the pump draws & put in a resistor to simulate the load if the driver circuit uses current to determine whether the pump is running or there could be a pressure sensor to trick....

I'm just shooting from the hip, since the drawing is incomplete & a bit fuzzy...

Am I missing something here: can't you just cut the wire and short the relevant ECU input(s) to 0V?

Randall, you got it ! Or put a switch in so that you can go back and forth between them if you want it (maybe for wife or kids).

IT "might" just be that you could even simply disconnect it since with no input it should fall to zero volts and stay there. Be sure to tape off the ends of the wires to prevent shorts.

I recently had a problem with my ABS/Traction control on my 99 Pontiac Grand Prix and while investigating the problem the manual suggested that the signal was actually a PWM duty signal. I did not look at on a scope or anything and I don't know if the Mercedes would be the same just giving you a heads up to make sure your not looking at the signal with a DVM and "filtering" the PWM signal. Good luck!

Shawn

Hey Guys,

Shawn33 makes a good point. It might not be as simple as cutting down or defeating an analog voltage. If it is Pulse Width Modulation, the apparent voltage read by the voltmeter will be very misleading. For example, the 1.3V reading would actually be a 0 to 5V pulse at a relatively slow cycle per second rate, (off most of the time). Since most meters in voltage mode will average this signal, it will appear as a small continuous voltage, and not be correct. The 5V reading would be when the signal is "on" most of the time, for the other end of the measurement range. See if your meter has a "frequency" mode, or borrow someones' who does, and run your "tests" again. (The FUN part!) Notice the readout at rest, then proceed to harder and harder maneuvers, watching the meter's readout (preferably by a brave passenger!), and see if the numbers start going up. If they do, and then fall back down as you stop the maneuvers, then you've got some type of PWM signal, and simply cutting down the voltage will only guarantee throwing a code by the ECU. If the meter reads 0V (accounting for a few stray readings caused by noise), then you've got a straight DC voltage, and it gets simpler. In the case of Mustang Cobras of the past few years, there has been a switch to turn off traction control for purposes like drag racing, (which is how I know about it), so that suggests to me that there are several types of schemes being used by the different manufacturers, so finding out just what type of signal Mercedes uses would be the first priority.

What is most likely is that each wheel sensor will output a certain pulse width for a given wheel speed, which the ECU will look at as a representative voltage, just as your meter does. It will then compare the other wheel sensors, and take action if any of them is reading too differently from the others. This will make it tough to get around, as you don't know just what the ECU is using to decide if everything's okay, or not.

So, what I would suggest is trying to feed just one wheel sensor output to all the other wheel sensor inputs to the ECU. This will eliminate the need for any external faking circuits. Plus, as an added bonus, this should work no matter what type of system Mercedes uses, since you'll be sending the proper signal, whatever it is, from just one sensor. The car won't know it's in a slide. It'll think everything's just fine! Also, you can set this up to a 4-pole switch (schematic upon request) to switch back to all 4 sensor inputs for safety, when you wish it!

So, wear your brain-bucket, and learn to counter-steer......a lot!! Also, as Garthh has suggested.....DO look into whether tampering with these sensor inputs would disqualify you under the "stock" rules. It would be a shame to get all this done, win a race, and get disqualified for an "illegal" modification! Be safe and Good Luck!

Hi Guys,

Again I don't know on Mercedes but on GM the wheel speed sensors feed back to a EBTCM (Electronic Brake and Traction Control Module) which does all of the processing of the signals and then sends a torque request to the PCM (Powertrain Control Module). No real difference from what cj2048 was saying just throwing it out there. Also on the Grand Prix is a TCS Off button but I've heard a lot of them are not 100% off, they may be qualified off, such as off if the vehicle speed is low enough or greatly reduced parameters for engaging, cars now a days go through great lengths to protects us from ourselves.

Shawn

Good point on PWM. This is where an oscope comes in handy, or if you do not have an oscope, ditch the DMM and switch to an old analog meter and just watch the needle pulse.

Why not rent an OBDII programmer and play around with the settings? I have not tried this but you should be able change the inputs/outputs with one. Look up some manufacturers and see what they are capable of.

I am not even going to try to suggest how to reduce the signal because it is probably a modulated signal and not a simple voltage divider fix. I will say it would better to go with the switch idea and turn it off it you find it too annoying. It will also improve your gas mileage if you are able to. The traction control is there for safety but at the expense of fuel mileage. That was tip given to me by a Delphi Engineer a couple of years ago while I was working on a dual brake sensor for their traction control system that was going to be used on all of GM vehicles in Europe and the Pontiac Montana mini van in the US.

What I will tell you is that the actual working voltage range is not 0-5vdc. It is generally 0.5 to 4.5vdc in automotive applications. Where around 0.2vdc to 4.75vdc is the linear range of the output and once outside that range, the output will go into cut-off (short) or saturation (open) for diagnostics purposes. This is a general standard used within the automotive industry regardless of region.