99 Jetta A3 - OBD connector cannot read
 

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.

> wrote:

> 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.

Does it have an aftermarket stereo upgrade? - that often causes major
issues with the OBD reading.
--
Steve H 'You're not a real petrolhead unless you've owned an Alfa Romeo'
http://www.italiancar.co.uk - Honda VFR800 - MZ ETZ300 - Alfa 75 TSpark
Alfa 156 2.0 TSpark Lusso - Passat 1.8 Turbo SE - COSOC KOTL
BoTAFOT #87 - BoTAFOF #18 - MRO # - UKRMSBC #7 - Apostle #2 - YTC #

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

> wrote in message
oups.com...
> 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.
>

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.

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.

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.

...... You let your son talk you into a car (doesn't dad/mom always know
best?), you bought it, and now you are getting it checked out?.... To be
honest this doesn't sound good from the get-go... But it's probably a pretty
easy fix, might just be a sensor or something.... you never mentioned the
driveablility symptoms... if there are none, it's not a big problem - as for
your fuse being good and you thinking there is a short circuit... well fuses
tend to blow with a short circuit (or your battery would drain increadibly
quickly and wires would literally melt) so you could have an open circuit (a
more common electrical condition, but something that pretty much all
non-electrical people call a short... everything is a "short" to most
people... most likely a broken wire would cause an open)
> wrote in message
ups.com...
> 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.
>

In rec.autos.makers.vw.watercooled, wrote:

>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.

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

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.

Sounds like an O2 sensor.... that's kind of how my old Digifant based 1991
Golf reacted when its sensor went. - Idle would be a bit faster some days,
drank gas.
> wrote in message
oups.com...
> 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.
>

Try this page.
http://obddiagnostics.com/DataSheet.pdf

JoBo

> wrote in message
ups.com...
> 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.
>