# CEL P0030 help



## mikelo320 (Jun 16, 2016)

Hey 

I just purchased a 2007 Jetta 2.5L 5 speed with 82,000 miles (my first VW). And of course the CEL came on a few days later. I scanned it and came up
with code p0030, heated o2 sensor. I changed the o2 sensor with a Bosch and the light came back. After doing some research i read to check 
to see if pins 3/4 are getting 12v, turns out I'm only getting 2.2v. I'm wondering what could cause this? It sounds like the ECM provides 
the power to the o2 sensor, does this mean I need a new ECM? 

I had a thought and please let me know if this is stupid. I was thinking I could piggy back off a switched 12V fuse and run a new source
for the power and splice it into the o2 sensor wiring harness at the plug. Do you guys think this would work? Could this cause any other
issues?

And if I do need an ECM where's a good place to buy from. 

Thanks in advance guys/gals.


----------



## le0n (Jun 12, 2013)

possibly a harness failure. these can happen when road debris comes in contact with them.

don't replace your ecu.


----------



## mikelo320 (Jun 16, 2016)

What's the best way of going about checking the wiring? Just visually check it? Where can I find a wiring diagram so I can see where the o2 sensor wires end? What's vagcom? Any thoughts on my other idea.

Thanks again.


----------



## le0n (Jun 12, 2013)

needle into the wire insulator and check continuity with a multimeter?

also, look for any ground to chassis wires coming from the upstream harnesses and make sure they are not corroded.

what specific o2 sensor replacement did you use? what it a universal kit?


----------



## mikelo320 (Jun 16, 2016)

le0n said:


> needle into the wire insulator and check continuity with a multimeter?
> 
> also, look for any ground to chassis wires coming from the upstream harnesses and make sure they are not corroded.
> 
> what specific o2 sensor replacement did you use? what it a universal kit?


It was the upstream and I used a specific bosch replacement o2 sensor. Not sure of the part number right now. 

When I tried looking at the harness it just combined with the rest of the engine harness. It looked un touched.


----------



## mikelo320 (Jun 16, 2016)

mikelo320 said:


> It was the upstream and I used a specific bosch replacement o2 sensor. Not sure of the part number right now.
> 
> When I tried looking at the harness it just combined with the rest of the engine harness. It looked un touched.


I checked with a multimeter between pins 3 and 4 and came up with 2V


----------



## le0n (Jun 12, 2013)

man, i completely apologize. for some reason i thought you were talking about the rear/o2 sensor on the cat. i must have been halfway awake or reading another post at the same time on a different forum.

anyway, that o2 sensor/harness are easy to inspect as you have done. and most likely the sensor kit had its own harness so you didn't have to do any wire splicing.

at this point, i'm wondering if it is a power relay that is not letting the full current feed the sensor heating element.


----------



## mikelo320 (Jun 16, 2016)

le0n said:


> man, i completely apologize. for some reason i thought you were talking about the rear/o2 sensor on the cat. i must have been halfway awake or reading another post at the same time on a different forum.
> 
> anyway, that o2 sensor/harness are easy to inspect as you have done. and most likely the sensor kit had its own harness so you didn't have to do any wire splicing.
> 
> at this point, i'm wondering if it is a power relay that is not letting the full current feed the sensor heating element.


No worries, thanks for the help. Which relay would it be?


----------



## le0n (Jun 12, 2013)

that, i don't know.

see if google gives you any hints.


----------



## le0n (Jun 12, 2013)

check your fuses under the hood.


----------



## mikelo320 (Jun 16, 2016)

le0n said:


> check your fuses under the hood.


I can't believe I missed that. Bad fuse! I'm stupid. Thanks a lot for the help.


----------



## le0n (Jun 12, 2013)

i guess when the sensor fails, it can do so in a way that blows the fuse.


----------

