Airbag Control Unit inputs

[ghostwalker]

Hi all. New poster here, longtime reader.

I'm trying to find more info on ACU inputs for a 2005 Sprinter. Specifically, I want to know what exact inputs/sensors the ACU needs to trigger airbags, and how it determines if/when and how "hard" to fire them. (FWIU, the T1N only has 2 airbags, so side curtains are a non-issue.)

Details are important, so any links to relevant technical resources on the ACU or any info on the trigger "algorithm" would be very helpful.

...And to mitigate eventual the SRS troubleshooting tips, there is nothing wrong with my airbags. I just want to know how they work in the T1N.

Thanks for any reply!

~GhostWalker

 

[sikwan]

In addition to the two airbags, the front seat belts have a one-use (similar to airbags) retracting spool when enabled.

Looking at the schematics, it looks like the info to trigger the Airbag Control Module come from the Engine Control Module and Central Timer Module. A single Dark Green wire is what triggers the ACM.

I didn't look any further as I'm sure there are sensors being using by the ECM and CTM that trigger the Dark Green wire.

 

[ghostwalker]

Thank you so much for your reply!

Understood regarding single wire to the ACM. I assume this makes the ACM simply regulate the force by which the bags and spool retractors deploy, not make the decision to trigger them (unless, of course, it uses data from the CAN bus to "decide").

Anyway, I guess that expands my question to include ECU & CTM inputs/sensors used for the airbags as well as, now, for the seatbelt retracting spools.

Basically, I'm just looking for a list of sensors and inputs (as well as maybe values) that would make the van decide to blow the airbags (or not).

Also looking for any insight into the decision making process ("algorithm") that brains it.

Thanks in advance for any technical info anyone can muster.

EDIT: Also any link to the ACM/ECU/CTM schematics you're using? Thanks!

~GhostWalker

 

[billintomahawk]

Ghost,
I have an '02 612.
I have been trying to reset the SRS light on my dash. It is lit.
Today I will remove the seats and try to check continuity to the ABM from the passenger squib wiring.
I am afraid I damaged my ABM unit when I drilled through the squib wiring grounding it. I repaired the wiring but it is still no go on communication.

I am unable to communicate via scanner with the ABM to reset/turn off the SRS light. And I assume I have no airbags on collision.

It has been a PIA for sure.

'02 T1N SRS light on

Hey everyone, I have had the SRS light on since I installed an auxiliary(house) battery under the passengers seat. Today I pulled the battery out and lifted the battery tray and sure as heck I drilled into a cable under the passengers seat base floor. The cable had a twisted pair of wires, blue...

sprinter-source.com

bill

 

[autostaretx]

EDIT: Also any link to the ACM/ECU/CTM schematics you're using? Thanks!

Since we don't know what diagrams you're working with, we can only start by pointing at the service manuals
2003: http://www.diysprinter.co.uk/reference/05 service manual.pdf
2006: http://diysprinter.co.uk/reference/2006-VA-SM.pdf
In this directory, you can pick up the "sub system" (Body, Chassis) manuals, too: http://diysprinter.co.uk/reference/
Section 8O (that's an "Oh") of the service manual is the "restraints" section.
Airbag Wiring diagrams are in section 8W-43, but they view the controllers as "black boxes".
The pinout for the ACM (airbag control module) is on page 8W-80-6, but does not include the optional side curtain call-outs.
(probably not available in US/Canada).
As far as i can tell, ALL of the ACM's connections are *outputs* (except for the power).
(although the "enhanced accident report driver" may be a bi-directional message wire)

The "training" pages don't speak of the seat belt/airbag systems (but some of the background info might say something): http://diysprinter.co.uk/reference/T1N_service_scans/

I would *suspect* that the Air bag controller module has all of its sensor internally, so that it can operate without requiring communication to other (perhaps optional) sensors like the ABS/ESP yaw sensors.
The T1N apparently offered optional side curtains (at least by 2006), for which there were external side-sensors.

The primary sensor (for a T1N) would be forward deceleration ... with only two or three "notches":

If you hit an obstruction a bit too hard (loading dock, parking lot bollard), it sets the "crash" status up one notch, which disables remote Locking.
(i call this "crash pending")
The sensor/controller will remain in that state until it's actively reset by a capable scanner.
Some scanners report on that status.
After that i'd guess that you only have two more levels: "mild crash" (gentle air bags) and "severe" (BANG!!)
But, who knows? There may only be one level for firing the airbags.

--dick

 

[autostaretx]

From section 8O of the 2006 service manual: (pages 8O-8 and -9)
(("safing" is pronounced "safe-ing"))

Concealed within a hollow in the center of the die
cast aluminum ACM housing is the electronic circuitry
of the ACM which includes a microprocessor,
an electronic impact sensor, an electronic safing sensor,
and an energy storage capacitor. A stamped
metal cover plate is permanently secured to the bottom
of the ACM housing to enclose and protect the
internal electronic circuitry and components.
An arrow printed on a label on the top of the ACM
housing near the rear provides a visual verification
of the proper orientation of the unit, and should
always be pointed toward the front of the vehicle.
--------------
Two sensors are contained within the ACM, an
electronic impact sensor and a safing sensor. These
electronic sensors are accelerometers that sense the
rate of vehicle deceleration, which provide verification
of the direction and severity of an impact. On
models equipped with optional side curtain airbags,
the ACM also monitors inputs from two remote side
impact sensors located within the left and right front
door step wells to control deployment of the side curtain
airbag units.
The safing sensor is an electronic accelerometer
sensor within the ACM that provides an additional
logic input to the ACM microprocessor. The safing
sensor is used to verify the need for a supplemental
restraint deployment by detecting impact energy of a
lesser magnitude than that of the primary electronic
impact sensors, and must exceed a safing threshold
in order for the airbags to deploy. Vehicles equipped
with optional side curtain airbags feature a second
safing sensor within the ACM to provide confirmation
to the ACM microprocessor of side impact forces.
This second safing sensor is a bi-directional unit that
detects impact forces from either side of the vehicle.
Pre-programmed decision algorithms in the ACM
microprocessor determine when the deceleration rate
as signaled by the impact sensors and the safing sensors
indicate an impact that is severe enough to
require supplemental restraint system protection.
When the programmed conditions are met, the ACM
sends the proper electrical signals to deploy the front
airbags and seat belt tensioners and, if the vehicle is
so equipped, either side curtain airbag unit.
The ACM also provides a hard wired electrical
crash signal output following a supplemental
restraint deployment event. This output is used to
signal other electronic modules in the vehicle to provide
their enhanced accident response features,
which include automatically disabling the engine
from running and unlocking all of the doors. However,
these responses are each dependent upon the
circuits, components, and modules controlling these
features remaining intact from collateral damage
incurred during the vehicle impact.
----------------------

--dick

 

[ghostwalker]

Wow! Thanks Dick! That was really helpful!

I was always under the impression airbag deployment took info from multiple sensors distributed throughout the vehicle (including the engine) to know exactly how to fire.

The service manual seems to indicate that everything needed to decide SRS deployment is internal, which does makes sense for maintenance purposes. (Interestingly, the '05 manual doesn't talk about a safing sensor at all which, I assume, makes the decision algorithm more rudimentary.)

It also doesn't talk about airbag deployment magnitudes, meaning airbags and spools always deploy with the same force when triggered?

Also, any official resource for the "notched" nature of the crash algorithm?

Thanks so much for your help!

~GhostWalker

 

[autostaretx]

I was always under the impression airbag deployment took info from multiple sensors distributed throughout the vehicle (including the engine) to know exactly how to fire.

Using other modules as a "family habits" guide, MBprobably uses the same air bag controller (ABC) in multiple car families, and just programs it to suit. Since the 2006 manual doesn't show the pins for the side-sensors, i suspect there *are* a bunch of "inputs" in that connector. Reading other MB service manuals (S-class, C-class, Vito (etc etc) might yield pay-dirt.

The service manual seems to indicate that everything needed to decide SRS deployment is internal, which does makes sense for maintenance purposes. (Interestingly, the '05 manual doesn't talk about a safing sensor at all which, I assume, makes the decision algorithm more rudimentary.)

Although the other manual i linked to starts with "05-VA" as a file name ... it REALLY IS a 2003 (OM612) manual.

By putting all of the eggs into the one module, they avoid accidental air bag deployment due to wiring harness damage elsewhere in the Sprinter (an all-too-common happenstance).

It also doesn't talk about airbag deployment magnitudes, meaning airbags and spools always deploy with the same force when triggered?

This is what other MB service manuals might hint at .... i'd say "or talk to a tech", except the T1Ns are now 15 years "in the past".

Ya know? The fabled Dr Andy Bittenbinder (now retired) might know a *lot* about this (and he certainly does know the T1N.
864-623-9110 Clemson SC (just W of Greenville) abittenbinder@yahoo.com

Also, any official resource for the "notched" nature of the crash algorithm?

That came up somewhere in the dim distant past as a reason the dashboard door lock button (and remote fobs) would cease locking doors.
It takes a T1N-smart (i.e. talks to the separate K-lines) scanner to clear that semi-fault. No lights display on the dash.

--dick

 

[ghostwalker]

Thanks for the reply, again!
___________________________

Using other modules as a "family habits" guide, MBprobably uses the same air bag controller (ABC) in multiple car families, and just programs it to suit. Since the 2006 manual doesn't show the pins for the side-sensors, i suspect there *are* a bunch of "inputs" in that connector. Reading other MB service manuals (S-class, C-class, Vito (etc etc) might yield pay-dirt.

Interesting. I'd assume the manual would be more complete than that, but maybe it's just not too relevant for servicing the vehicle. As long as the tech knows where to plug in what harness or to buy a new one, it's thorough enough for that purpose, I suppose.

Although the other manual i linked to starts with "05-VA" as a file name ... it REALLY IS a 2003 (OM612) manual.

The vehicle I am working on is from the 2004/2005 age range, so I suppose an OM612 manual would work just fine.
Is there a better service manual for '05 Sprinters?

By putting all of the eggs into the one module, they avoid accidental air bag deployment due to wiring harness damage elsewhere in the Sprinter (an all-too-common happenstance).

Makes sense. It would probably need a lot more smarts to detect/deduce faulty readings than feasible for the mid-00s.

This is what other MB service manuals might hint at .... i'd say "or talk to a tech", except the T1Ns are now 15 years "in the past".

Ya know? The fabled Dr Andy Bittenbinder (now retired) might know a *lot* about this (and he certainly does know the T1N.
864-623-9110 Clemson SC (just W of Greenville) abittenbinder@yahoo.com

Thanks for the reference! I'd feel kind of strange phoning him out of the blue on this, but the email address should work nicely. (On a side note, I hope he doesn't mind all his info posted on here. )

That came up somewhere in the dim distant past as a reason the dashboard door lock button (and remote fobs) would cease locking doors.
It takes a T1N-smart (i.e. talks to the separate K-lines) scanner to clear that semi-fault. No lights display on the dash.

Hmm... Interesting. This means the ACM microcontroller probably has some memory component to it as well. Good to know.

EDIT: I should probably also ask, any good recommends for a "T1N-smart" scanner? Would the typical iCarsoft or Acutel scanners work for this? (Not that I have any problems w/ my SRS system. Just an aside.)

Also, this tidbit of info might be useful info for @billintomahawk and his problem above.

~GhostWalker

 

[autostaretx]

Interesting. I'd assume the manual would be more complete than that, but maybe it's just not too relevant for servicing the vehicle. As long as the tech knows where to plug in what harness or to buy a new one, it's thorough enough for that purpose, I suppose.

MB tends to work with a "swap parts" attitude. Less "real thinking" diagnostic time, higher profit margins.
Also: the air bag controller is a *very "sensitive" safety system ... they don't want the legal liability of a two-black-thumbs tech messing around inside it. Quite like an airliner's black box (send to Boeing/Airbus for readout).

The vehicle I am working on is from the 2004/2005 age range, so I suppose an OM612 manual would work just fine.
Is there a better service manual for '05 Sprinters?

The 2005 has an OM647 engine. Just like my 2005.
The best bet service-manual-wise is to fetch the 2004 manuals ... the 2005 is mid-way between it and the 2006.
This directory has the full set of 2004 and 2006 manuals (note the Powertrain, Transmission, Body, Chassis and parts catalogs)

DIY Sprinter

Building a campervan and sharing the love

diysprinter.co.uk

This directory has the deep-background training manuals: http://diysprinter.co.uk/reference/T1N_service_scans/

Makes sense. It would probably need a lot more smarts to detect/deduce faulty readings than feasible for the mid-00s.

You may be surprised how little the components have advanced since then (in many ways). They want "proven reliable", not "new and shiny" (except for the communications group).

Thanks for the reference! I'd feel kind of strange phoning him out of the blue on this, but the email address should work nicely. (On a side note, I hope he doesn't mind all his info posted on here. )

He invites and solicits the phone calls (usually it's "leave a message and he'll call back"... which he does).
If you lay out what you're seeking in the first (even recorded) phone call, he could assemble documentation before calling

He has been a long-time contributor to the forum (for at least 17 years) and frequently leaves his number in his postings.

Hmm... Interesting. This means the ACM microcontroller probably has some memory component to it as well. Good to know.

I wouldn't hazard a guess without reading a scanner's report on the manufacturer. They're probably Bosch, but MB sources modules from a number of vendors.

EDIT: I should probably also ask, any good recommends for a "T1N-smart" scanner? Would the typical iCarsoft or Acutel scanners work for this? (Not that I have any problems w/ my SRS system. Just an aside.)

There's a "Scanners" sub-forum. The AP808 multi-system (or Pro) is possibly the "best under $350", but each of the other contenders will have some one (or two) features that makes *it* the perfect choice for a particular customer.

I have the (far) cheaper AP200 ($70, requires smartphone and net connectivity when first turned on (to verify license))
I also have the "DAD" (Dr Andy's Diagnostic) which is an old CarSoft (not iCarSoft) hardware lump that Andy "grey imported".
Although it "speaks K-line", i don't really know if it can clear an SRS fault. (it can report Crash state) Requires a Win 95 or XP PC.

--dick

 

[ghostwalker]

Thanks again!

MB tends to work with a "swap parts" attitude. Less "real thinking" diagnostic time, higher profit margins.
Also: the air bag controller is a *very "sensitive" safety system ... they don't want the legal liability of a two-black-thumbs tech messing around inside it. Quite like an airliner's black box (send to Boeing/Airbus for readout).

Unfortunate for anyone investigating the technology, but it makes perfect sense. Not good to have people messing around where they shouldn't.

The 2005 has an OM647 engine. Just like my 2005.
The best bet service-manual-wise is to fetch the 2004 manuals ... the 2005 is mid-way between it and the 2006.
This directory has the full set of 2004 and 2006 manuals (note the Powertrain, Transmission, Body, Chassis and parts catalogs)

DIY Sprinter

Building a campervan and sharing the love

diysprinter.co.uk

This directory has the deep-background training manuals: http://diysprinter.co.uk/reference/T1N_service_scans/

Very good to know. Wonder why the '03 manual is mislabelled. At any rate, 2004 body manual seems to have some additional specific info, so it works just as well.

On a related note, the manual does mention a "three deployments" limit for the ACM, which sounds similar to the "three levels/notches" mentioned earlier. From the manual:

The Accident signal will set a DTC in the CTM and the door locks will not work until the DTC has been erased. The ECM will set a DTC if the Accident Report circuit is shorted to battery voltage. The ACM saves the deployment record and after three deployments the ACM must be replaced.

(2004-VA-Body.pdf, Section 3.1)​

EDIT: Any possible info on which manual's description might be closer to the ACM used in the '05? Would the '06 manual be more accurate (w/ the side curtains and safing mechanism) than the '04 from what you understand? When was the safing mechanism introduced in the T1Ns?
______________________

You may be surprised how little the components have advanced since then (in many ways). They want "proven reliable", not "new and shiny" (except for the communications group).

That's probably for the best, although my impression is that newer cars take in far more information for the SRS than earlier models owing to the sheer complexity of newer systems. Can't be sure of the brain 'hardware' at any rate, but certainly in software.

He invites and solicits the phone calls (usually it's "leave a message and he'll call back"... which he does).
If you lay out what you're seeking in the first (even recorded) phone call, he could assemble documentation before calling

He has been a long-time contributor to the forum (for at least 17 years) and frequently leaves his number in his postings.

Good to know. Then I don't feel so bad bugging him with weirdly specific inquiries. Thanks!

I wouldn't hazard a guess without reading a scanner's report on the manufacturer. They're probably Bosch, but MB sources modules from a number of vendors.

I guess I'll have to invest in a good scanner after all, then.

There's a "Scanners" sub-forum. The AP808 multi-system (or Pro) is possibly the "best under $350", but each of the other contenders will have some one (or two) features that makes *it* the perfect choice for a particular customer.

I have the (far) cheaper AP200 ($70, requires smartphone and net connectivity when first turned on (to verify license))
I also have the "DAD" (Dr Andy's Diagnostic) which is an old CarSoft (not iCarSoft) hardware lump that Andy "grey imported".
Although it "speaks K-line", i don't really know if it can clear an SRS fault. (it can report Crash state) Requires a Win 95 or XP PC.

I'll take a look a said sub-forum. I was hoping to avoid any purchases, especially ones which require rolling a whole laptop, though the detailed reports may be worth it in some circumstances.

Also...

Requires a Win 95 or XP PC.

Maybe I can run it in a virtual machine. Not a fan of having to find old hardware to run those things.


Thanks for the clarifications!

~GhostWalker

 

[autostaretx]

Very good to know. Wonder why the '03 manual is mislabelled.

It's not mis-labeled, it just has a more (to human eyeball) vague labeling system (i think it was "5th year" (of T1N's) or something like that)
Just as the "VA" in its part number signified the "Sprinter" body style.

On a related note, the manual does mention a "three deployments" limit for the ACM, which sounds similar to the "three levels/notches" mentioned earlier. From the manual:

The ACM saves the deployment record and after three deployments the ACM must be replaced.

What they're talking about there is that the bag-firing circuits get weakened by each full pop-the-bags activation.
After three bag-activating crashes they're not deemed reliable enough to keep using.

Similar to a "surge-protection" plug strip ... the active component (an MOV (metal-oxide varistor)) is damaged each time it has to "eat" greater-than-rating (200 to 400 volts) spikes. After a few kicks they should be replaced (good ones have a warning light).

EDIT: Any possible info on which manual's description might be closer to the ACM used in the '05? Would the '06 manual be more accurate (w/ the side curtains and safing mechanism) than the '04 from what you understand? When was the safing mechanism introduced in the T1Ns?

Since MB (like most German mfg's) slips in improvements throughout a model run, you'd have to access their electronic parts catalog (EPC) with the sub-assembly serial numbers applicable to *your* Sprinter ... the full "datacard" includes those SA numbers.
The parts catalog refers to them in the "which variant of this part" listing.

Sending your VIN to member sailquik will get back that "complete" version of the datacard, or signing up for MB's EPC ($79 per year).

StarTek Info

www.startekinfo.com

In the mean-time, you can download the "basic short list" (no SA numbers) from one of these: https://www.datamb.com/ , https://www.lastvin.com/ , http://mbepc.net/f/vin/

Maybe I can run it in a virtual machine. Not a fan of having to find old hardware to run those things.

Some stuff you can, some you can't. Part of it was old VMware breaking under Win10. There have been threads by folks who have managed to get the various packages running.
I just have kept an old Win 98 or XP (i forget which) for the purpose. Takes over 5 minutes to boot.
The "Chinese C3 Clones" can be bought with a hard drive or complete Thinkpad as a package.

--dick

 

[ghostwalker]

Wow! Good batch of info again, Dick! I appreciate all the quick replies to all my questions/assumptions!

It's not mis-labeled, it just has a more (to human eyeball) vague labeling system (i think it was "5th year" (of T1N's) or something like that)
Just as the "VA" in its part number signified the "Sprinter" body style.

Very good to know. Makes sense.

What they're talking about there is that the bag-firing circuits get weakened by each full pop-the-bags activation.
After three bag-activating crashes they're not deemed reliable enough to keep using.

Similar to a "surge-protection" plug strip ... the active component (an MOV (metal-oxide varistor)) is damaged each time it has to "eat" greater-than-rating (200 to 400 volts) spikes. After a few kicks they should be replaced (good ones have a warning light).

Okay, thanks. That's very good information. I might just acquire an unused ACM and crack it open to see how it's wired internally and to probe around with a multimeter.

Sending your VIN to member sailquik will get back that "complete" version of the datacard, or signing up for MB's EPC ($79 per year).

I'll give it a shot. Would rather have more details than less.

In the mean-time, you can download the "basic short list" (no SA numbers) from one of these: https://www.datamb.com/ , https://www.lastvin.com/ , http://mbepc.net/f/vin/

Thanks for the links!

I just have kept an old Win 98 or XP (i forget which) for the purpose. Takes over 5 minutes to boot.
The "Chinese C3 Clones" can be bought with a hard drive or complete Thinkpad as a package.

I'm sure I could scrape together one if I go that route rather than relying on 'clones'. Reliability seems okay from what I read, but I'd rather not be plugging a rando computer from Alibaba into my van. I'm sure there are some good suppliers, but it makes me nervous.

Only issue for the custom build option (other than sourcing the software) would probably be getting the it working, which seems to be hit or miss from what I understand. But I'm sure there are plenty of resources around here to troubleshoot any problems that arise.

~GhostWalker