DBW: Pedal Position Sensor

[Enclavet]

I was testing my PPS sensors to Pectel today and noticed something:

The 2 PPS sensors are wired to AIN1 and AIN3.

When the PPS is at position 0 (not depressed) I get these readings:

PPS1: AIN1: .7v
PPS2: AIN3: .35v

When I depress the pedal all the way I get this:

PPS1: AIN1: 4.5v
PPS2: AIN3: 2.25v

I then looked at the factory wiring diagrams for my car and noticed an extra resistor on the PPS2 going to AIN3.

I have 2 questions:

Should the signal coming from PPS2 be reversed so that when the pedal is not depressed I should get 2.25v and when it is depressed it should be .35v?
Why would the factory put that extra resistor for PPS2 to divide the voltage?

[Enclavet]

It seems I found the answer to my question about whether the second PPS sensor should read exactly half PPS1.

Here is an excerpt from the article about BMW DBW systems:

The pedal position sensor or accelerator pedal module is powered by an exact voltage of 5 V from the DME
control unit. The pedal position sensor or accelerator pedal module is equipped with two completely
independent, mechanically coupled sensors. Both sensors output a voltage signal corresponding to the
current pedal position. For safety reasons, two sensors are used in order to determine any faults. Sensor 2
always generates exactly half the voltage of sensor 1 so that a short-circuit of both sensors can be detected.

[Neel]

The Pectel ECU is designed to work with a variety of DBW systems and as a result can tolerate a variety of setups. The main requirements are two separate sensors; how those signals work with respect to each other does not have to be exactly 1/2, opposite, etc. The error checking with respect to Pedal position is done by monitoring the differences in calibrated values and the resultant throttle motion.

[Max]

Good to see your PPS's voltages have values like mine. I'm running a S54 in an E36, using a E46 M3 pedal, SQ6v2-41.

My problem is that I can't get DBW to enable. I have experimented with many PPS curves (both linear and non linear user defined) that are fine on their own, but have now hit "Error in PPS sensor curve. Min separation test failed. Engine will not start" using either type of sensor curve.

Can anyone explain the minimum separation test. Also, which type of curve is better linear or non. I assume that a non linear curve gives you better throttle response.

Given the differing voltage values between the two sensors, what curves work.

Thanks,
Max

[Neel]

Sounds like you have some limits wrong. First off though, we need to upgrade you to our newest firmware. This can be done free of charge but involves sending us the ECU. Then provide me with a chart that shows minimum and maximum voltages for TPS, TPS2, PPS and PPS2 for throttle closed, throttle open, pedal 0%, pedal 100%.

I'm writing a tech bulletin on all of this and will give more details soon.

[Max]

Some kind of tech bulletin would be great. The dearth of information on DBW is significant.

A tech paper I have from BMW states that both PPS's shouldn't be under .5V at closed throttle or the signal is non plausable and the stock ECU should go into a DBW failed mode. We know that's not the case as PPS2 does read .35V or so at 0% throttle and E46 M3's are not all limping around.

I'll gather up the sensor info and ECU when I'm at the track this weekend. I'll shoot you an email when I'm ready to ship.

Max

[Neel]

A tech paper I have from BMW states that both PPS's shouldn't be under .5V at closed throttle or the signal is non plausable and the stock ECU should go into a DBW failed mode. We know that's not the case as PPS2 does read .35V or so at 0% throttle and E46 M3's are not all limping around.

I don't know - off the top of my head I'm pretty sure I've seen M3's under 0.5V at closed throttle. It doesn't matter to me as we're doing standalone ECUs and whatever it says, as long as its consistent and linear, we can make it work.