99 Jetta A3 - OBD connector cannot read

Jun 24, 2005 10 Replies
A

Why did I let my son talk me into buying a used Volkswagen. OK, here is my latest disaster problem. Went to have the car inspected. It fails because the shop cannot get any readings from the OBD connector. So I go home and check the fuse. It's good. Then I turn the ignition on, and no check engine light is lit. So it sounds like I have a short. I figured let me check the connector at the ECM, but I can't find the ECM. Where is it? According to the Volswagen service manual, it should be somewhere at the left side of the engine compartment, but there is nothing there. Can someone help me here?



Also, any other ideas on how to troubleshoot this problem. I don't have any special tools, just a multimeter.



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S

Does it have an aftermarket stereo upgrade? - that often causes major issues with the OBD reading.

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W

Possible causes

1- check engine bulb burnt out 2- check engine bulb was removed to hide the fact it was on and former owner/selling dealer lot didn't fix it 3- can't talk to ECM, does it have an non-VW radio 4- ECM is located in cowl area under wiper linkage
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A

Well, I found the ECU. Now I can't figure how to get the connector off. Can anyone help me here.

Also, there is no aftermarket radio. It's a Volkswagen premium radio, but it's possible it was added after the original radio.

I don't think the bulb is burnt out because I'm guessing there is no power to the OBD connector either. Anyone know which pins to check to verify this.

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A

Well, I found the ECU. Now I can't figure how to get the connector off. Can anyone help me here.

Also, there is no aftermarket radio. It's a Volkswagen premium radio, but it's possible it was added after the original radio.

I don't think the bulb is burnt out because I'm guessing there is no power to the OBD connector either. Anyone know which pins to check to verify this.

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R

The ECU connector is under the dashboard, somewhat in line with where the steering wheel is on the A4's... Probably in a similar place on the A3's.

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T

If it goes on when you turn the key on and have not yet started the engine, the light is not burnt out.

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A

Good point about the battery drain. So it may be an open. I have gone through the wiring diagrams. The power from the main fuse comes in on pin 23 and then goes out to the indicating light on pin 6. If I can figure how to get the harness off the ECU, I'll check for voltage on pin 23. I would think I have to have voltage, because if the ECU has no power, the car wouldn't run. It does run, pretty well actually, although it appears to be eating gas a little bit, and there is no fast idle speed when the engine is cold which I would expect.

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J

Try this page.

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JoBo

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A

Well, I took out the whole instument cluster, and lo and behold, the problem surfaced. The indicating light bulb had been removed. Great way to fix engine light problems. I switched a bulb to try it and the light comes on fine now and then goes off, so at least that is not a problem. Now on to the next problem of why the OBD connector is not reading.

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