U020800 - Lost Communication With “Seat Control Module A”

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pdmjo
New Member

Posts: 8

U020800 - Lost Communication With “Seat Control Module A” Oct 3, 2022 10:01:59 GMT

Quote

Post by pdmjo on Oct 3, 2022 10:01:59 GMT

Hey everyone,

I recently installed some seats which aren't compatible (connector wise) with my car, as such i can't run power to the seats so i'm getting an airbag error due to the airbags in the seats not being able to deploy.

Is there any way to make inactive the terminal which searches for a connection to this seat only?
I want all other airbags to still work, just not search for an airbag within the seat?

Any ideas greatly appreciated!

Thanks!

Error code is below:

19 Gateway

System description: GW MQB High
Software number: 3Q0907530L
Software version: 4326
Hardware number: 3Q0907530C
Hardware version: 436
Serial number: 0007256136
ODX name: EV_GatewNF
ODX version: 013044
Long coding: 030500347F085900FB07225A9E0F00010001070000000000000000000000

Subsystems:
System description: J367-BDMHella
Software version: 9070
Hardware version: H10
Serial number: 9763196604

System description: E221__MFL-DC1
Software version: 0040
Hardware version: H11
Serial number: 29170002808060057493
Long coding: 2DFFFF

System description: E881 BedieFPA
Software version: 0410
Hardware version: 001
Serial number: 000000091171RAG002CU
Long coding: 464553

Trouble codes:
U020800 - Lost Communication With “Seat Control Module A”
static
Date: 2022-10-01 19:15:34
Mileage: 55760 km
Priority: 2
Malfunction frequency counter: 1
Unlearning counter: 212
Supply voltage, terminal 30: 11.7 V
Terminal 15: On

dv52 (Australia)
Moderator

Posts: 6,064

U020800 - Lost Communication With “Seat Control Module A” Oct 3, 2022 22:18:24 GMT

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Post by dv52 (Australia) on Oct 3, 2022 22:18:24 GMT

hmm...... so, if I understand correctly, you want to disable the seat occupied recognition control unit, on the front passenger seat (it's called "J706" in the wiring diagram) on a 20th century car?

wow-no offense intended, but good luck with that !!!

Seriously - there is very little information in the public domain about the software switches on the long-code string for the air-bag module (it's called "J234"). You could search through the adaptation channels for the module - but my quick look didn't identify any candidate channels.

The other matter of concern is that playing with the air-bag module has the accompanying danger of igniting the air-bags - and if that happens, getting the car to run again is not a trivial task!!

Don

Please don't ask questions about car coding/repair via the forum "Message" function. The better place for such dialogue is in the forum proper. That way, the wider expertise of the entire forum community can be applied to solve your problem - thank you

pdmjo
New Member

Posts: 8

U020800 - Lost Communication With “Seat Control Module A” Oct 5, 2022 9:16:37 GMT

Quote

Post by pdmjo on Oct 5, 2022 9:16:37 GMT

Hey Don,

Yep that's literally it lol.

Rather than pay the money for someone to figure out how to rewire the seats to be compatible with my car, I thought I could perhaps just disable the 'feature' altogether.

Accidentally igniting the airbag wasn't something which I thought of, so perhaps I'll have to either a) pay someone or b) learn to live with it.

Thanks for the info about the long-code names, will keep investigoogling.

Appreciate the response Don.

Last Edit: Oct 5, 2022 10:31:52 GMT by Thirsty

dv52 (Australia)
Moderator

Posts: 6,064

U020800 - Lost Communication With “Seat Control Module A” Oct 5, 2022 20:47:06 GMT pdmjo likes this

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Post by dv52 (Australia) on Oct 5, 2022 20:47:06 GMT

pdmjo :

Your project intrigued me - so I did some searching and it appears to be a surprisingly simple task.

Here's how the passenger side occupant sensor is wired on a VW mk7/mk7.5:

So, as you can see - the passenger sensor (it's called "G554") is a simple 2 x pin device that's terminated on a 3 x pin connector (called "T3" in my diagram).

It appears from my "investigoogling" (nice term- thanks) that the sensor can be easily simulated by connecting a 2.2ohm 1/2 watt 5% tolerance resistor to pins #1 and pin #2 !!

Of course, for legal and moral reasons, I'm not suggesting that you do this - I'm just making an observation and sharing the information !!

Don

Last Edit: Oct 5, 2022 20:49:01 GMT by dv52 (Australia)

pdmjo
New Member

Posts: 8

U020800 - Lost Communication With “Seat Control Module A” Oct 13, 2022 4:18:37 GMT

Quote

Post by pdmjo on Oct 13, 2022 4:18:37 GMT

You've certainly given me my homework for the week, Don!

Electronics is new to me, but from what I've deduced so far about transistors, would it potentially overload if I was to get into a crash which deployed the seat's airbags, sending a signal to the transistor which has nowhere to go/re-route the signal?

Yes - investigoogling is a great term I found in a book some years ago!

Oh, I would never dream of actually doing any of this... It's a purely hypothetical experiment for science...

Last Edit: Oct 13, 2022 9:51:06 GMT by Thirsty

dv52 (Australia)
Moderator

Posts: 6,064

U020800 - Lost Communication With “Seat Control Module A” Oct 13, 2022 23:11:16 GMT pdmjo likes this

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Post by dv52 (Australia) on Oct 13, 2022 23:11:16 GMT

pdmjo : Arrhh......... a new-bee into the mystic arts of transistors - enjoy the learning journey!!

So.... here's the thing about this stuff - my picture above was thieved from VW's wiring diagrams (hopefully without infringing copyright). This means that whilst the diagram is an accurate reflection of how different components are "wired" together - the diagram says absolutely nothing about why the separate bits are wired in this manner!

I'm not aware of any VW information related to MQB platform cars (like your mk7) that exposes the internal circuitry of their components. In general, this information is sequestered from the public gaze and it's normally only available to the wizened troglodytes that labor feverishly in the VW dungeons (meaning of course that this information is proprietary knowledge)!!

This notwithstanding, for folks here with a background in control-system theory (after-all, these are "control" modules, so their design is based-on a set of well established principles), or for someone with an interest for things electronic - it's possible to intuit how stuff works!!

So, with the caveat that what follows is a guess that is prone to wild excursions of technical fantasy and gross errors - maybe consider the following:

At it's essence, a control module like the airbag module is a simple device that gathers data from the outside world and based on this information, it makes decisions. It ain't any more complex than this at a fundamental level.

If I extrapolate my previous reductive sentence, a module has just 2 x kinds of connections to the outside world which are known as "inputs" and "outputs". The other important thing about control modules is something called "feedback" - but I won't complicate matters by talking about this (except to introduce the concept)!

For the purpose of your question, it's clear that the passenger sensor (let's call this "G554") falls into the category of a module "input". It senses when a passenger is seated and it likely works by changing the status of switch in the seat via a human type weight.

Now in this case, G554 is most definitely not a simple switch because a simple switch has a status of ON, or OFF. For reasons that I suspect are safety related, the design engineers @ VW appear to have made the passenger sensor more discriminating than a simple ON/OFF status change. Instead, the decision circuits in the airbag module appear to look for a preset resistance (rather than a resistance of either zero, or infinity). In fact, I suspect that the internal module circuit looks for a defined electrical current, or a set voltage level that is determined by the preset resistance - in this case between module pin#34 and earth (see my diagram)!

Again without knowing anything about the internal module design, I suspect that module pin#34 is an open collector/emitter circuit as you infer (these pins normally use these type of transistor circuits). As shown in my diagram, the wire that connects to this pin leaves the module and it meanders to the outside world and eventually it terminates onto pin #2 of G554.

So, think about your transistor "potential overload" concern. With G554 installed, there is a realistic chance in a crash that the passenger sensor wire between the airbag module and G554 will either open circuit, or it may be shorted to earth somewhere in the wiring loom! It would be criminally negligent for the design engineers at VW to allow the airbag module to fail if this happens.

Almost without exception, input (and output) pins on modern control modules are overload-proof - part of the circuit design is invariably a load-sensing facility that deals with these type of outside-world events. I would be extremely surprised if this didn't happen on the passenger sensor pin of an airbag module.

Finally - I reiterate again (tautology intended) that I'm not recommending that anyone modifies an airbag module because of the resultant safety issues

Don

Last Edit: Oct 13, 2022 23:19:26 GMT by dv52 (Australia)

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