NefMoto > Technical > Diagnostics > B5 S4 - Could a bad AIRBAG module keep me from connecting to the ECU?
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Author Topic: B5 S4 - Could a bad AIRBAG module keep me from connecting to the ECU?  (Read 17747 times)
GWerks
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« Reply #15 on: January 16, 2013, 11:58:06 AM »
Quote from: corradovolksb on January 16, 2013, 11:38:17 AM
I attached the radio wiring diagram. It looks like there isnt a K wire that goes to the radio. In the pictures it looks like you have canbus wires (the orange with brown tracer and orange with purple tracer) that go to the black connector so that means that your radio is prob not the cause of your issue and it could be a problem with your instrument cluster because the gateway moudule is in the cluster and allows canbus communitcation to all of the modules. I have had some cars that the cluster will not allow communication and after unpluging it and pluging it back in everything comes back online but you said you have already reset the cluster and it still does not work. I have had abs modules cause the canbus to go down also but you also said that you have tried leaving it unplug and still cant communicate so that pretty much rules that out. have you tried just unpluging the abs moudle by itself and leave everything else pluged in?

Thanks for the diagram, I was about to post it.

As of right now, I have the cluster disconnected, ABS module, radio, climate control, and AIR BAG module. It's weird because when I try to connect to ENGINE with VCDS, it takes about 15 seconds for the warning to come up, almost like if I had just turned on the key when I clicked on Engine.

The K line wire to the radio is green/blue.

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DiscoPotato
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« Reply #16 on: January 16, 2013, 01:53:25 PM »
Ive had a radio problem pull down all communications before.

Figure out that radio wiring I bet that is your culprit.
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GWerks
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« Reply #17 on: January 17, 2013, 04:00:04 PM »
I have checked the K line and CAN wires on the radio harness and they look intact. I'm going to see if I could have a bad OBD2 port, I will be testing the voltage between pins 7 (K-line) and 4 (ground), I guess I will find out then.

Things I have done:

Disconnect ABS module (remains disconnected)
Disconnect AIRBAG module (remains disconnected)
Disconnect cluster
Disconnect radio (remains disconnected)
Disconnect climate control unit (remains disconnected)
Disconnect central locking pump (remains disconnected)
Disconnect headlight leveling module (remains disconnected)
Disconnect ultra sound sensor module (remains disconnected)

So every module K-line related has been disconnected, going to see if the K line wire has power, if it does, then I will know it's a bad obd2 port or something else.
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GWerks
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« Reply #18 on: January 17, 2013, 04:00:39 PM »
The multimeter read -040 - -043 ohms between K line wire at the OBD2 port and ground. Does this mean it's working?
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savages4
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« Reply #19 on: February 10, 2013, 12:10:20 PM »
I had a similar problem with my buddy's 2000 s4, it would only connect to the ECU if the car was running.  After he replaced his ABS module for some reason these problems have gone away? 
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darkshado87
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« Reply #20 on: October 28, 2013, 05:25:45 AM »
Quote from: GWerks on January 17, 2013, 04:00:39 PM
The multimeter read -040 - -043 ohms between K line wire at the OBD2 port and ground. Does this mean it's working?
your last post you said you where checking for voltage at pins 7 and 4, why where you checking ohms? if you check for ohms with power to k line you can destroy your multi-meter ohms is for resistance with no power
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adam-
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« Reply #21 on: October 28, 2013, 05:21:56 PM »
Quote from: darkshado87 on October 28, 2013, 05:25:45 AM
your last post you said you where checking for voltage at pins 7 and 4, why where you checking ohms? if you check for ohms with power to k line you can destroy your multi-meter ohms is for resistance with no power

What?

Ohms is used to determine the resistance of a wire, between two points.  The amount of current flowing through that wire is irrelevant to the multi-meter.

Only thing I can think of is that you mean measuring current, but instead of checking current flow, you short it out, to measure that max current that the circuit can supply.  If this max current is more than your multi-meter can handle, then, yes, it could break it.  Pretty sure that's why they invented fuses though.

Still not sure what you mean at all though.. haha

I would run a fresh line to the ECU, bypassing EVERY other k-line.
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darkshado87
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« Reply #22 on: October 29, 2013, 05:26:13 AM »
Quote from: adam- on October 28, 2013, 05:21:56 PM
What?

Ohms is used to determine the resistance of a wire, between two points.  The amount of current flowing through that wire is irrelevant to the multi-meter.

Only thing I can think of is that you mean measuring current, but instead of checking current flow, you short it out, to measure that max current that the circuit can supply.  If this max current is more than your multi-meter can handle, then, yes, it could break it.  Pretty sure that's why they invented fuses though.

Still not sure what you mean at all though.. haha

I would run a fresh line to the ECU, bypassing EVERY other k-line.
clearly you dont know what you are talking about! a ohm meter is used to test resistance  (no shit), when a ohm meter is used it puts out its own small electrical charge to test power should be removed, (if kline has 12 volts due to a misswire from a radio install and you check from kline to ground your running a charge threw the meter if YOU know it or not, that can short out the meter) i was mostly questioning why he checked for ohms when he said he was going to check for voltage
smart ass

"Remember!
You can only test resistance when the device you're testing is not powered. Resistance testing works by poking a little voltage into the circuit and seeing how much current flows, its perfectly safe for any component but if its powered there is already voltage in the circuit, and you will get incorrect readings
You can only test a resistor before it has been soldered/inserted into a circuit. If you measure it in the circuit you will also be measuring everything connected to it. In some instances this is OK but I would say that in the vast majority it is not. If you try, you will get incorrect readings and that's worse than no reading at all."

http://learn.adafruit.com/multimeters/resistance quoted
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adam-
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« Reply #23 on: October 30, 2013, 04:04:40 AM »
Incorrect readings, yes.  But you won't break it.
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turbopro
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« Reply #24 on: October 30, 2013, 06:10:43 AM »
Quote from: adam- on October 30, 2013, 04:04:40 AM
Incorrect readings, yes.  But you won't break it.

wrong again sorry

"An ohmmeter is a device that measures resistance. It is connected in parallel across the
resistance to measured. You should NOT measure the resistance of a resistor that is still
part of a circuit. You will probably destroy the ohm-meter, certainly you will measure the
wrong resistance. In practice first disconnect all leads of the resistor to be measured, so
no electric current runs through the resistor, except for the current supplied by the battery
inside the ohm-meter itself."

quoted  http://www.physics.rutgers.edu/ugrad/161/LabwmcorManualsPDF/ResistanceOhmsLaw/wm8corResistanceOhmsLaw.pdf
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turbopro
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« Reply #25 on: October 30, 2013, 06:14:10 AM »
for real?
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