Welcome to my audi, I can't connect through OBD with the engine. You can connect with air conditioning for it. 1.8 lpg engine. Anyone have an idea what could be? I read that it can be through lpg but how to get around it?

If you now have a compact green-black with green-red and red from the immo can, does the car start? If it starts, cut the red that goes from this connection to the immmo can, if the car does not start, then check if you can make a diagnosis.

What equipment do you have The car starts?

Yes, the car is working. They tried vagem and viakenem. Interfaces are functional because they work in other cars.

So what to do in this situation?

Or maybe an emulator was installed and someone did not connect the diagnostic line.

And then he would not read everything probably? And it combines with air conditioning and ABS.

No, if there is an emulator it is connected only to the ECU and not to the rest.

Hello, I used to do a topic with VW and there was an emulator in the immo can and I couldn't connect to the ecu if someone installed the emulator and didn't connect the WI line K lines together there is no ECU diagnostics, but you can check if you have the immo off key wrap in aluminum foil so that only the tip protrudes and start the car when you start it, you do not have immo

I did not check with the key but the immo box is but only 3 cables come from it. It is also like a torn ankle next to nothing with green cables. So this will be an emulator in the immo box?

Hi, green cables t line K and W line if they are connected diagnostics, but the car probably won't start

Audi A4 B5 (1.8 LPG) - Unable to Connect to ECU via OBD, Works with Air Conditioning

golabek008 12192 17

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#1 16934360 03 Jan 2018 23:11

golabek008 golabek008

Level 9

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Post #1
16934360 03 Jan 2018 23:11

Welcome to my audi, I can't connect through OBD with the engine. You can connect with air conditioning for it. 1.8 lpg engine. Anyone have an idea what could be? I read that it can be through lpg but how to get around it?
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#2 16934372 03 Jan 2018 23:14

spinacz spinacz

Level 42

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Post #2
16934372 03 Jan 2018 23:14

What equipment do you have
The car starts?
#3 16934611 04 Jan 2018 06:34

golabek008 golabek008

Level 9

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Post #3
16934611 04 Jan 2018 06:34

Yes, the car is working. They tried vagem and viakenem. Interfaces are functional because they work in other cars.
#4 16934629 04 Jan 2018 07:18

andrzej20001 andrzej20001

Level 43

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Post #4
16934629 04 Jan 2018 07:18

Immo off can be done
#5 16934841 04 Jan 2018 10:31

golabek008 golabek008

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Post #5
16934841 04 Jan 2018 10:31

So what to do in this situation?
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#6 16934869 04 Jan 2018 10:49

spinacz spinacz

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Post #6
16934869 04 Jan 2018 10:49

Or maybe an emulator was installed and someone did not connect the diagnostic line.
#7 16935039 04 Jan 2018 12:23

golabek008 golabek008

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Post #7
16935039 04 Jan 2018 12:23

And then he would not read everything probably? And it combines with air conditioning and ABS.
#8 16935043 04 Jan 2018 12:25

spinacz spinacz

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Post #8
16935043 04 Jan 2018 12:25

No, if there is an emulator it is connected only to the ECU and not to the rest.
#9 16935194 04 Jan 2018 13:40

adamski123 adamski123

Level 21

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Post #9
16935194 04 Jan 2018 13:40

Hello, I used to do a topic with VW and there was an emulator in the immo can and I couldn't connect to the ecu if someone installed the emulator and didn't connect the WI line K lines together there is no ECU diagnostics, but you can check if you have the immo off key wrap in aluminum foil so that only the tip protrudes and start the car when you start it, you do not have immo
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#10 16936837 04 Jan 2018 23:57

golabek008 golabek008

Level 9

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Post #10
16936837 04 Jan 2018 23:57

I did not check with the key but the immo box is but only 3 cables come from it. It is also like a torn ankle next to nothing with green cables. So this will be an emulator in the immo box?
#11 16937398 05 Jan 2018 11:38

adamski123 adamski123

Level 21

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Post #11
16937398 05 Jan 2018 11:38

Hi, green cables t line K and W line if they are connected diagnostics, but the car probably won't start
#12 16937853 05 Jan 2018 14:57

golabek008 golabek008

Level 9

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Post #12
16937853 05 Jan 2018 14:57

So you can't do with the emulator and the connected K and W lines so that you can fire and check the errors only without firing?
#13 16937911 05 Jan 2018 15:38

spinacz spinacz

Level 42

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Post #13
16937911 05 Jan 2018 15:38

Connect these K and W, then check if you are talking about the equipment from ecu and the rest of the car. I did not have a knock, what is the case that the emulator blocked the diagnosis come apparently there are those that have this disadvantage. Write what resulted from the combination of K and W, the car should start without a problem.
#14 16937924 05 Jan 2018 15:47

adamski123 adamski123

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Post #14
16937924 05 Jan 2018 15:47

You have to see if it can do it, if not put a switch
#15 16939759 06 Jan 2018 11:52

golabek008 golabek008

Level 9
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Post #15
16939759 06 Jan 2018 11:52

I connected the cables but nothing came of it. I noticed that it does not connect with the climate. I will add pictures of these cables because I don't know if it should be like that.

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#16 16939771 06 Jan 2018 11:56

golabek008 golabek008

Level 9

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Post #16
16939771 06 Jan 2018 11:56

It follows that black and green combined with red from the can of immo. I closed with green-red but nothing came out. On one of the pictures is also a connection of several cables in which is red and green so I have no idea if it should be?
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#17 16940968 06 Jan 2018 19:17

spinacz spinacz

Level 42

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Helpful post
Post #17
16940968 06 Jan 2018 19:17

If you now have a compact green-black with green-red and red from the immo can, does the car start?
If it starts, cut the red that goes from this connection to the immmo can, if the car does not start, then check if you can make a diagnosis.
#18 16950238 10 Jan 2018 16:19

golabek008 golabek008

Level 9

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Post #18
16950238 10 Jan 2018 16:19

I did as you wrote and can be connected. I did it on the switch and it is even possible to read errors on the firing if the switch on the running engine is switched on. Thanks for the help
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Topic summary

✨ The discussion revolves around an Audi A4 B5 with a 1.8 LPG engine that cannot connect to the ECU via OBD, although it can connect through the air conditioning system. Users suggest potential issues such as an emulator installed in the immobilizer (immo) that may not be properly connected to the diagnostic lines. Solutions proposed include checking the connections of the K and W lines, ensuring they are correctly wired, and using a switch to facilitate diagnostics. One user successfully managed to connect and read errors by modifying the wiring setup.
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FAQ

TL;DR: In this Audi A4 B5 case, 1 switch restored ECU diagnostics; “I did it on the switch.” [Elektroda, golabek008, post #16950238]

Why it matters: If your OBD reads HVAC/ABS but not the engine ECU, a simple K/W-line fix can save hours of guesswork for 1.8 LPG owners.

Quick Facts

Symptom pattern: OBD connects to air conditioning and ABS, but not to the engine ECU. [Elektroda, golabek008, post #16935039]
Likely cause: immobilizer emulator or a missing/incorrect K–W diagnostic line connection. [Elektroda, spinacz, post #16934869]
Practical fix: tie K and W lines or add a toggle switch to restore ECU comms. [Elektroda, spinacz, post #16937911]
Confirmation tip: “wrap the key in aluminum foil” test indicates immo-off behavior. [Elektroda, adamski123, post #16935194]
Tools used and verified: VAG/Viaken interfaces worked on other cars; the A4 still started and ran. [Elektroda, golabek008, post #16934611]

Why does my Audi A4 B5 read HVAC/ABS but not the engine ECU over OBD?

Because the engine ECU’s diagnostic line is interrupted or rerouted, often by an immobilizer emulator or miswired K/W lines. Other modules (HVAC/ABS) sit on separate diagnostic lines, so they still reply. Restoring the K–W path brings the ECU back online. [Elektroda, spinacz, post #16934869]

What are the K-line and W-line in this context?

They are single-wire diagnostic lines used on older VAG cars. The ECU expects K and sometimes W lines present to communicate. If these lines are cut, not bridged, or hijacked by an emulator, the scanner cannot talk to the ECU. [Elektroda, adamski123, post #16937398]

Could an immobilizer emulator block ECU diagnostics?

Yes. If someone installed an emulator and didn’t connect the diagnostic line correctly, ECU diagnostics are unavailable while other modules still work. Reconnecting K and W restores access. [Elektroda, spinacz, post #16935043]

How can I quickly test if my car is immo-off?

Try the foil-key test. Wrap the key in aluminum foil so only the metal tip is exposed, then start. If it starts, the immobilizer is disabled. [Elektroda, adamski123, post #16935194]

What wiring colors did owners see when fixing this?

One owner reported green/black and green/red wires tied with a red lead from the immo can. He used those to sort the K/W connection and diagnose. [Elektroda, golabek008, post #16939771]

Will joining K and W lines stop the car from starting?

No. A helper advised joining K and W, then testing start and diagnostics. The car should start normally once the lines are correctly connected. [Elektroda, spinacz, post #16937911]

What’s the simplest working fix reported in the thread?

A toggle switch between the diagnostic lines. The owner confirmed “I did it on the switch” and could read errors even with the engine running. [Elektroda, golabek008, post #16950238]

Do VAG/Viaken interfaces fail here, or is it the car?

The interfaces were fine. They worked on other cars. The A4 still started and ran, indicating a vehicle-side diagnostic line issue, not tool failure. [Elektroda, golabek008, post #16934611]

My climate control also stopped connecting later—what does that imply?

It suggests broader diagnostic wiring issues, not just the ECU path. Re-check the splices and any emulator connections affecting shared signal routes. [Elektroda, golabek008, post #16939759]

How do I implement the switch-based workaround?

Identify the green/black and green/red diagnostic wires near the immo box.
Insert a simple toggle switch to bridge the K and W lines when needed.
With the switch on, connect your scanner; switch off after. [Elektroda, golabek008, post #16950238]

Is there an edge case where K/W reconnection still fails?

Yes. Some emulators block diagnostics regardless of K/W bridging. In that case, add a switch or re-route around the emulator to regain access. [Elektroda, spinacz, post #16937911]

What if my immo box shows only three wires—does that change things?

It can indicate a modified setup or emulator presence. Trace those three leads and look for a nearby broken plug or spliced greens to locate K/W. [Elektroda, golabek008, post #16936837]

Can LPG conversion be the reason for no ECU comms?

The thread points to immobilizer/emulator wiring rather than LPG. The car with 1.8 LPG ran fine; fixing K/W restored ECU diagnostics. [Elektroda, golabek008, post #16950238]

How do I know the fix actually worked?

You should establish ECU comms and read fault codes. The owner confirmed successful live diagnostics even on a running engine after adding the switch. [Elektroda, golabek008, post #16950238]

What’s a quick expert tip from the thread?

“Connect these K and W, then check.” Start there before complex steps; it often restores ECU communication immediately. [Elektroda, spinacz, post #16937911]

Any concrete numbers I can look for when inspecting?

Look for three wires at the immo module in modified setups and a single added switch bridging two diagnostic leads to re-enable OBD ECU access. [Elektroda, golabek008, post #16936837]

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