I have an airbag light on my dash which has come on in the past and has been reset without problems.

However it came on a couple of months ago and I took it to my dealer who connected it via the 20-pin round connector under the bonnet and said that there was no communication with the ECU, so he could neither diagnose the problem or turn the light off.

I've since tried an aftermarket airbag reset tool (off ebay) which has worke don another Z3 but comes up with an error code saying no communications awell.

So, has anyone else come across a "broken" round diagnostic cap on their car? I haven't got an OBD2 connector on my car (i t's a 1999 but a European car which didn't have this until 2001). There is power to the cap as the ebay tool lights up and allows to try and check for codes but it won't return anything.

is it only the SRS module that wont communicate?

if you can talk to other modules in the car such as general module then the SRS module is toast

the engine and trans share one K line, so talking to them doesnt count

all chassis systems share a second K line so if you can talk to other chassis modules like ZKE then the diag line is working

is it only the SRS module that wont communicate?

if you can talk to other modules in the car such as general module then the SRS module is toast

the engine and trans share one K line, so talking to them doesnt count

all chassis systems share a second K line so if you can talk to other chassis modules like ZKE then the diag line is working

Hi, thanks for that but nothing at all is working (problem was only highlighted whe nteh airbag came on out of the blue and I tried to switch it off). So there is no communication with anything at all.

try unplugging the SRS module

sometimes they go crazy and lock the K lines, usually happens right about the same time as a mysterious SRS light comes on
solid sign of a defective module

simply unplug it and try to connect to any other module on the car
if you have comms then replace the SRS module

You should have 12v on the K line (pin 20) and the K2 line (pin 17)

What year is your car? The port inside the car for the years 2000 and prior do not work. You'll have to use the port under the hood which will require an addaptor. Ask me how I know!:rolleyes

try unplugging the SRS module

sometimes they go crazy and lock the K lines, usually happens right about the same time as a mysterious SRS light comes on
solid sign of a defective module

simply unplug it and try to connect to any other module on the car
if you have comms then replace the SRS module

Ok thanks, I will try that!

Am I right in thinking that the airbag module is located in/behind the centre console? Is it easy to identify? (does it have a manufacture name on it or something?)

What year is your car? The port inside the car for the years 2000 and prior do not work. You'll have to use the port under the hood which will require an addaptor. Ask me how I know!

It's a UK car, 1999 so it doesn't have an OBDII port (I looked!), and found out they didn't have them until 2001.

You should have 12v on the K line (pin 20) and the K2 line (pin 17)

I assume I've got some power somewhere to it as I tried a friend's airbag reset tool (Peake Research one off ebay I believe) and it operated (lit up) when it was connected but wouldn't do much else.

Are they (pin 17 & 20) both ignition-switched lives?

Ok thanks, I will try that!

Am I right in thinking that the airbag module is located in/behind the centre console? Is it easy to identify? (does it have a manufacture name on it or something?)

should be under the center console somewhere
not sure where exactly on your car

should say MRS on it i think

17/20 are "bus" lines and they are pulled high when idle. They should have the voltage on them all the time.

I found out (the hard way) that some of the Z3 roadsters, year 99 I believe got EWS III, instead of what virtually all other E36 cars got which is EWS II.

I'm now "stuck" with an EWS III dme/ews III module/key "set" that I can't do much with for a MRoadster euro 3.2 Z3

(what a PIA when I un-intentionly send this to a customer with a EWS II harnessed engine, and he couldn't start it. Not much surprise there)

Anyone know of an online source to look up the wire diagrams for EWS III styled MZ3 cars?

Alex.

It's in the 99 wiring diagram. It also says that only m versions got EWS III.

Just to update (I'm still having problems!).

I've now tried all the above suggestions (disconnecting Airbag module etc), also disconnecting the battery for over 5mins to drain power, and I've checked all the diagnostic pinouts from the diagnostic cap to the ECU to no avail; I still can't get ANY communication/diagnostics.

I want to try and understand more on how the car's systems work; which unit stores the error codes that a diagnostic machine would interrogate and communicate with? is it the main DME/ECU?

Having the same issue, 2000 MZ3. I have both the Peake reset tools and all the sudden they both stopped working. Neither one powers on and there is no power going to pins 17 or 20 (or any other) on the diagnostic connector under the hood.

I have used both of these tools for years without a problem. The only thing I can think of is that the car was inspected and passed it’s annual state inspection by the state of Texas. They check your light bulbs, tires, and plug in a scan tools to check emissions, I believe. I was there when they did this and they didn’t run into any issues. However, they plugged into the connector inside the car. This was the first and only inspection for this car. I have always only used the connector under the hood, which now isn't getting any power.

I quickly check the fuses and they all look fine. I disconnected the battery for a few hours but still the same problem.

Could this be related? Could they have disabled the diagnostic connector under the hood somehow Any ideas...?

I get power (12v constants and ignition switched) when I should but nothing works.

I've now had it on a BMW machine, a peake reset tool and also tried a friends universal OBDII code reader with a BMW 20-pin convertor and none work.

Does anyone know how the system works?; ie where are the error codes (airbag light, engine check lights, abs faults etc) stored? (is it centrally like the engine ECU, or is it each individual control module).

It ended up being a fuse in my case (#26). I didn't find it until the second time around.

----
Fuse 26 10A hot in run and start pin 16.

Fuse 42 hot in accy, run and start pin 4.

Fuse ? in the black box under the dash hot in run and start pin 14.
----

sometimes some module pulls down diagnosis bus and you cannot diagnose your car at all.
to find out which module it is you have to disconnect all modules one by one and try to diagnose your car. when diagnosis bus starts to work you have found your problem.
ecu
central locking module
airbag
abs
speedo
automatic gearbox module
ews
and so on

i do many diagnostics on engines ( 20-40 cars in week) and sometimes have this trouble. when i am in a hurry i just disconnect white yellow and white purple wires from connector that connects engine wiring harness to car main harness and i can work with ecu.in older cars its 1 car from 20 that has this problem.
disconnecting these wires will not help you to diagnose your airbag problem so you have to go through this module disconnecting procedure.
other way is to cut these wires just after diagnostic connector, cut them next to airbag module and connect diagnostic connector wires directly to airbag diagnostic module wires.

Thanks for the prior note...

That was a very good idea, and an interesting problem that I bet not too many people have encountered.

I'm always amazed at the wisdom experience brings with it.

(any of us that uses these tools sporadically might never encounter that 1 in 20 cars that does this, but if you do that many each week..... well, you've been there and done that....

Stored in memory...

Alex.

sometimes some module pulls down diagnosis bus and you cannot diagnose your car at all.
to find out which module it is you have to disconnect all modules one by one and try to diagnose your car. when diagnosis bus starts to work you have found your problem.
ecu
central locking module
airbag
abs
speedo
automatic gearbox module
ews
and so on

i do many diagnostics on engines ( 20-40 cars in week) and sometimes have this trouble. when i am in a hurry i just disconnect white yellow and white purple wires from connector that connects engine wiring harness to car main harness and i can work with ecu.in older cars its 1 car from 20 that has this problem.
disconnecting these wires will not help you to diagnose your airbag problem so you have to go through this module disconnecting procedure.
other way is to cut these wires just after diagnostic connector, cut them next to airbag module and connect diagnostic connector wires directly to airbag diagnostic module wires.

Thanks for the info!

I know where the ABS and airbag modules are but not the others; could you tell me roughly where I'd fine them? Thanks again.

Most are behind the glovebox of LHD cars since you have a RHD I'm not 100% certain on which side they will be I know the microfilter is on the left always I kinda figure the modules are going to be on your right side.

Hi,

I have a similar problem to CW12, ref my tread :
BMW modic-3 diagnose problem, as of 11-nov.

Does anyone know the quickest way of isolating the I- and K-bus from the D-bus? ( without cutting the cable(s)...:-) )

Patrick S seems to have quite a lot of experience troubleshooting connection-problems, and he's mentioning somewhere to disconnect I/K bus...
My car is an E39 1998 model high IKE, which serves as a bridge between the D-bus and the I- and K-bus etc.
When checking pin-20(TxD) in the 20-pin diag-connector, it was ca 2,4V after i turned the ignition on(pos-2) and back off again(pos-0/1).
With the ignition on in pos-2, it's ca 10,8V.
Minimum voltage should be 2V on pin-20, and im wondering if it's shorted to B+,and jamming the D-bus, or if it should raise to close to B+ with the ignition on...?!?

Any ideas...?

regards
Tor

i and p bus connectors in e39 are behind glove box- whats wrong with cutting cables and finding the problem. if you have modic3 then use measuring system and documents! all info is inside there, so use it.
everytime i buy modic from ebay, test leads are almost new or never used:rolleyes