Automatic Stability Control+Traction (ASC+T)

[DaveAZ]

Edit to explain this thread: I wanted to retain ASC+T (Traction control) and ABS (Anti-lock brakes) without allowing ASC+T to interfere with the engine power output with its extra throttle body.
This would allow traction control to only sense and activate the brake(s) at a wheel(s) that lost traction. Sounds pretty good, right? I think I resolved it by the end of the thread. Once it has been tested in detail I will post my findings of my solution. As usual for me, this goes in depth and may take some effort to read. Post #9 is BMW's explaination of ASC+T, and you need to understand how it functions before you can mess with it effectively. It also has acronyms defined if you get lost.

If you are looking to do this yourself you can skip all the X69 harness connector stuff; that was because I had an engine swap involved that required extra steps as it also interfered with the ASC-T wiring.
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I bought a E36 1994 325IS that originally came with manual transmission and ASC-T (Automatic Stability Control+Traction). The engine was trashed.

I just swapped in a complete 1995 M3 drivetrain: gauges, 3.0 engine, manual transmission, entire front and rear subframe assemblies including limited slip differential, suspension & brakes, and brake master cylinder.

The ASC+T in the car's body became a bit of an afterthought.

I didn't install the ASC+T throttle body since I don't like the idea of the car cutting into power output against my will. I also don't like the additional intake airstream resistance. (Do people ever disable only the throttle body?)

The standard ABS hydraulic unit is different from the ASC-T hydraulic unit. The ASC-T hydraulic unit has four output lines instead of two like the standard ABS.

According to the E36 Bentley Manual, ASC-T cars require something special in the process of bleeding the brakes that they do not reveal- very secretive... I read on bimmerforums that it involves activating the system during the bleed process, but I have no clue and need to bleed it immediately, too.

So, my questions:
1. Should I still consider using ASC+T, even though it will be unable to control the throttle and limit my power output?
2. Should I suck it up and install the ASC+T throttle body?
3. Should I retain the ASC+T components on the car?
4. Will removing any of the components cause issues? Edit answer: If you remove the throttle actuator, you lose ABS! (solution below)
5. How do I properly bleed the brakes? Am I stuck finding someone with a certain diagnostic computer system and paying them?


Search terms: ASC Traction Control AST DTC

[bmwdirtracer]

The unfortunate part is that if you don't do something, you've also lost ABS. Traction control, we'd all happily do without; ABS is good.

I did an electrically similar, but more difficult swap, putting a Euro '98 S50 in my friend's /99 M3. We still haven't got around to the massive and scary rewiring necessary to use the ABS, mainly due to the fact that the engine ended up having a bearing issue, so it's been sent back to the seller. If your M3 donor had no ASCT, you've got no way to run your abs as currently plumbed and wired. The asct computer needs interface with the correct DME to do it's job: if you are running a dme from a non-asc M3, you won't be able to run ASCT anyway, forget the throttle body.

All I'm hoping to do for my friend's car is restore ABS; we have the non-asc ABS computer, which will have to have complex rewiring: and replumbing to pressure both rear brakes through 1 line split into 2. I thought rewiring the X20 connector was rough, the X69's a real nasty bitch, when one car doesn't even have one!

By studying and comparing factory wiring diagrams for the two cars involved, you'll be able to understand the plumbing involved too. You WILL need FACTORY diagrams, though: it's the only place where the X20 and X69 connectors appear; just be thankful you didn't have the X6309( I think - I have notes, but I'm not going there right now) to deal with: that would be the third similar round connector on newer cars, which deals with OBD2 issues. That one's gone forever on the '99.....euro cars have no such connections!

Bleeding the brakes shouldn't be an issue; since you really can't make it ASCT, you won't need to cycle the valves electronically, which, by the way, ONLY THE DEALER CAN DO, (requires a GTI computer). However, to be honest, I've never found a need to do this. I use a combination of a pressure bleeder with a vacuum bleeder, simultaneously, and have never found a system that didn't respond properly due to un-computer-bleeding, even after swapping ABS hydraulic units.

However, please note that the dealer on Maui refuses to do a paid brake bleeding for a cash customer by factory computer methods without computer-proving the need, first, even if their own former tech requests it. GRRRR.

I've done a few swaps, you may pm me if I can help. Factory diagrams I cannot easily provide; I had to beg.

[DaveAZ]

DME: I have the red label 413 DME that came in the body. Since the build date is 06/94 it should be a Bosch Motronic M3.3.1 without EWS; the same boards as the DME that came with the M3. I'm under the impression that I could use this DME with S50 engine and the aftermarket (Dinan) M3 performance chip. Chip manufacturers warn against using the chip with 413 DME, but I believe they mean the 413 in M3 1995+ with EWS. I don't know if they add anything to the DME for ASC+T, but it is worth retaining it just in case. I think ASC-T has a computer of it's own behind the glovebox.

Wiring: I can try to retain the X69 connector and trace the four wires from the old harness and install them in the car. Hopefully they are each a straight shot to open connectors at the DME harness. This is the only absent wiring from the car right now. The throttle body wiring is part of the body harness and is intact. I left the throttle plate position sensor connected to the wiring but I'm guessing it will always read closed, since it is just dangling with no throttle body to connect to. The computer will likely know the throttle body controller is disconnected and respond by fault code, if not disable. I may be able to pull the electrics off the ASC+T throttle body to fool this, too.

Wheel speed sensors, etc: I'm hoping this stuff is all the same at the wheels, since I swapped the M3 suspension on. I think ASC+T uses the same components at the wheels as regular ABS.

ASC+T throttle body: I still have this; the rubber intake bellows part 13-54-1-703-694-M200 between the Air Flow Meter & Throttle Body is cracked and would need to be replaced. It is unique to the ASC+T configuration. I really don't want a power governor on my car...

I'm not sure what would be missing that would not allow ABS to properly function. Is the Euro engine ABS problem a DME situation that doesn't apply to my car, or am I missing something?

[bmwdirtracer]

Since the car runs, EWS has been dealt with.

ASCT definitely has it's own computer, the question is, does your present dme have inputs and outputs to deliver the speed signals needed by the ASCT computer? If it does, you should be able to complete the wiring from your body's X69, (with or without that connector) and regain full ASCT, then just push the button to shut it off when you want to play. Given the option, that's the route I'd choose to most easily regain ABS. You'll likely have to compare diagrams to make sure, but I would guess that incorporating the secondary throttle body might be your best way to regain abs, then shutting off the asct for playtime. As long as the diameter of the secondary tb isn't unduly restrictive for the M3 motor, this may be your best bet.

I am not sure whether abs will operate with the secondary throttle body absent, with an otherwise connected asct system.

[DaveAZ]

I pulled the X69 harness connector and four wires from the old harness and put it in the car. The wires were straight runs. I matched the same connection ports on the DME harness and put it in. I also yanked some other part off the ASC+T throttle body that appears to be a temperature sensor and added it to the car. I'm still resisting the throttle body swap!

http://img.photobucket.com/albums/v329/biomechanical_clone/IMG_0092.jpg

Why this was a priority, I don't know... I still have not bypassed the alarm disable and started the car. I'm only assuming everything else has been dealt with. I guess I want it to be perfect when I turn the key.

[bmwdirtracer]

Thorough saves expensive mistakes; good job, being careful. Sounds like you have a better situation than I do, as the Euro MZ3 dme doesn't have the connections for the 4-channel ASCT in the US M3.

[DaveAZ]

I Finally got the wiring diagram!
Here are the components that I pulled off the ASC-T throttle body, as they are now connected to the car with the standard throttle body to help prevent fault codes:
Top is: E104 Throttle Flap Heater
Middle is: M93 Auxiliary throttle position sensor
Bottom is: THROTTLE ACTUATOR. What am I supposed to do with those wires? That part is long gone...
http://img.photobucket.com/albums/v329/biomechanical_clone/IMG_0096.jpg

[DaveAZ]

Nine days later... Link: FOUND IT! (http://forums.bimmerforums.com/forum/showthread.php?p=9444754#post9444754) This long thread went into detail about fixing this situation. In order to fool ASC+T into thinking the throttle actuator is still attached and to leave ABS functioning, I just need to bridge the two wires at the throttle actuator connector with a 10-Ohm Resistor.


I = V/R (I = 12/10 = 1.2A)
P = I*V (P = 1.2*12 = 14.4 Watts)

NTE makes a resistor that is 10 Ohms and 25 watts. I got it for a dollar at Fry's electronics. SKU# 7 68249 11042 2
http://img.photobucket.com/albums/v329/biomechanical_clone/IMG_0128.jpg
I used that metal sheet as a resting surface to do my sloppy soldering.

I also did this mod at the switch: Shut off Automatic ASC+T at startup (http://www.jogger-egg.com/kbob/asc+t.html)
If anyone tries that mod, it helps to know that the polarity of the capacitor is indicated by arrows on a stripe pointing to the negative terminal.

If all works out I will retain ABS and ASC-T will never activate unless I push the button.
The button will be if I want the car to pulse an individual rear brake upon traction loss of a wheel at speeds below 25mph in addition to my LSD.

Issues:
1. I'm not sure how the computer would interpret the throttle position sensor not changing after the actuator thinks it moved the butterfly. (turn on the Throttle Flap Heater, then fault?) (I may have found the answer to this in my post below.)
2. The ASC light on the dash will remind me of the headache I went through to disable it. I can live with that. (Edit- 1995 M3 gauges have no ASC light!)

Edit: From what Dave '328iJunkie' says, I can leave the throttle position sensor unplugged to fault out the ASC-T and prevent it from turning on. Any 10-Ohm resistor completing the throttle actuator circuit will keep the ASC-T from faulting out the ABS, since it will never power up.
If I deside to never use ASC-T, I can simply remove the throttle position sensor and I will still have functional ABS.
This could wind up being a great drag racer setup. I'll post more info asfter I have the car running and actually use it.

[DaveAZ]

From the BMW TIS (Technical Information System): ASC+T from the 1990 750 series (similar to others)

Interface
Whenever the ignition is switched ON, the ASC+T system is in operation. The indicator lamp goes off when the engine is started. As soon as the system is activated, for example, if the accelerator setting is excessive for the given road conditions, the ASC lamp in the instrument cluster flashes to alert the driver. If the ASC+T system fails or is switched off, the ASC lamp remain ON permanently.

Function
When wheel spin is detected, the control circuits can intervene. If at least one wheel exhibits a speed
difference of 1.8 MPH, the ASC+T system is activated (intervenes).

ASC+T controls wheel slip under acceleration (wheel spin) through four regulating functions:
Throttle valve regulation
· Ignition timing regulation
· Rear brake regulation
· EGS shift characteristic regulation

The ASC+T ignition adjustment function is carried out by the DME control unit, in response to digital signals issued by the ASC+T control unit. The DME control
unit contains operation-related maps from which it selects precise data on ignition adjustment in response to these signals.

Select Low/Select High Traction Control
All control circuits of the ASC+T system operate according to the select low or select high principle, i.e., the degree of intervention depends on critical deviation in the event of wheel spin The select low principle is applied if differences are detected between the left and right sides, or if both driven wheels exhibit spin and the vehicle speed is above 25 mph. In such cases, both rear wheels are braked together (only briefly) to allow the spinning wheels to regain traction.
Select low regulation is achieved in the following sequence:
1. Throttle valve opening angle regulation
2. Ignition timing regulation
3. Rear brake control

The select high principle is applied at road speeds below 25 mph, and if differences in spin are detected between the driven wheels. It provides individual brake application to either driven wheel, thus slowing the spinning wheel and transferring the torque to the wheel with greater traction. The select high function also raises the reference value range for wheel spin.
Select High Regulation is activated in the following sequence:
1. Rear brake control
2. Throttle valve opening angle regulation
3. Ignition timing regulation
Speed is calculated for each wheel and an average per axle is calculated. The speed of the nondriven front wheels serves as a reference speed. The critical reference value for control purposes is defined according to vehicle speed and vehicle acceleration.

Safety Logic
The ASC+T (All Season traction+traction control) system is integrated with the ABS (Anti-lock Braking System.) The two systems share the same control unit, and receive wheel speed information from the same wheel sensors. However, the two systems operate independently from each other, and each is capable of functioning in the event of the other's failure, provided no shared electrical component is involved. In order to obtain a highly effective and sensitive control system, it was necessary to coordinate the ASC+T system with the EML (Electronic Motor Load regulation,) DME (Digital Motor Electronics,) and EGS (Electronic transmission control) systems.

If a fault affecting the control function occurs, the ASC+T warning light immediately comes ON. If a fault occurs while ASC+T is active, ASC+T is switched off and the throttle valve opening angle is slowly adjusted to the specified pedal value by EML in a ramp fashion.
The ASC+T system interfaces with the digital motor electronics and can be switched off by each of the control units if the inputs are wrong or implausible. All lines with a safety-relevant function are monitored for signal plausibility and potential. Interfaces and line errors are assessed as faults and the system is switched off.
An ASC+T intervention process is not necessarily interrupted in the event of a fault; it can continue until wheel spin is eliminated. If the ASC+T system fails, the vehicle can be driven as a conventional vehicle without ASC+T. The ABS, EML, and DME functions remain independently effective. Whether the ASC+T system is switched on or off, the entire safety circuit is active. The two microprocessors fitted are redundant and monitor each other. Self-test cycles also run continuously. Monitoring software defines interfaces and plausibility tests for identifying faults in sensors and actuating elements. If one of the processors identifies a fault, ASC+T is immediately switched off and the indicator lamp is activated immediately, but the ASC+T system continues the intervention process until its completion. If a fault is detected in an electrical component which is also utilized by ABS, the ABS system is also switched off.
The interface with EML was specially designed using digital pulse width modulated signal transmission (at 100 Hz frequency) for safety reasons. The ASC+T control unit continuously transmits the throttle valve control signal to the EML control unit, and checks whether any throttle valve opening adjustment signal is permitted by safety thresholds defined by its programming.
For purposes of fault diagnosis, the fault memory can be read in the form of a flash code. Refer to the appropriate repair manual or electrical trouble-shooting manual for further details.

And now, in german:

[DaveAZ]

Video: Why it is good to not completely disable traction control