# DTC P0042 - HO2S Heater Control Circuit Bank 1 Sensor 3 **IMPORTANT READ THIS!!**



## DaveMK123 (Mar 25, 2005)

I don't normally go to the forums for repair information but, after the :banghead: I've run into this code I felt it necessary to post this so no one else gets burned by the incorrect information printed by Bentley in the factory repair manual.

I was asked to take a look at a vehicle for a family friend since I'm a former Vw tech and do some work on the side out of my garage at home. The vehicle was a 2004 Jetta 2.0L with a BBW engine code.

For those who aren't aware, the BBW is a odd ball code which was only produced for 2004-2005 years which utilizes 3 oxygen sensors (upstream, center in cat, and downstream).

The vehicle had several codes to start but, reoccurring was a P0042 aka Heater Circuit Malfunction for Bank 1 Sensor 3. http://engine-codes.com/p0042_volkswagen.htmlWith that being said I started to diagnose the heater circuit according to the Bentley repair information.

According to Bentley, Bank 1 Sensor 3 is sensor # G465 is located in the center of the catalytic converter. OEM part # 06A906262CB. 








(I know a lot of this information is above and beyond but, I figure for future reference someone may like to have it on hand)

-I followed the procedure to test the heater circuit on the center 02 sensor. Measuring resistance with a DVOM I get a reading of 9 ohms. This is within spec. (1-20 Ohms)

-Next I checked for voltage according to the Bentley. Oddly there was no key on voltage as suggested in the repair manual but, there was 13v on start up so I presumed that was correct.

At this point I decided that it was possible the sensor was faulty, perhaps intermittently. Seeing as it had voltage and it was only throwing the heater circuit code.

I purchased a Bosch direct replacement sensor, # 16575 and proceeded to install it. Cleared DTC. Upon start up the code immediately returned (no light since the vehicle was not driven to for drive cycles). Again cleared DTC and again immediately code returns as a hard fault.

At this point I began to consider the fact I had a faulty wire somewhere so I went back through testing the heater circuit, again measuring resistance of the new sensor, 10 ohms again in spec. I check voltage again, present. I checked for the signal to the ECM which supply ground to turn the heater circuit on and off.

I found there to be no resistance for the wire from the sensor to the ECM connector so I proceeded to replace the wire from the sensor figuring this should resolve the issue.

Afterwards I cleared the DTC and again tested it by started the vehicle. Again, the DTC immediately returns. Hard fault.

What the F*ck!  This is baffling me. 

The only other thought I had at this point is the ECM is faulty. It's not going to ground as it should. Despite a very useful value block I checked with Vag-Com that shows the signal switching "on" and "off" I don't know of a way to test the internal operation of the ECM for the completion of the ground signal so I started to chalk it up to that.

This is where things get interesting or I should say,

I decided to do a little bit of research before calling my friend who is a Vw dealer technican to see about having the ECM checked for replacement.

I came along a post on another forum site http://jettajunkie.com/vw-jetta/archive/index.php/t-7845.html Upon reading through the oddly similar steps taken I saw this post.



> billh1012
> 05-24-2010, 11:55 AM
> ok here we go. i got my car back from the dealership. from what they are telling me is that the bentley manual is wrong. everything they have for my car list the oxygens sensors down the line from front to rear. according to the bentley manual it shows pre-cat 1, post-cat 2, and on cat 3. they said it could have been updated since the bentley was made but whatever.
> 
> ...


*The Answer* - for those who want to skip my epic story and get to the bottom line.

I went home last evening. Decided to follow the steps the dealer tech above had taken to see if I was in fact looking at the wrong sensor all along.

I first disconnected the center 02 (one I had replaced). With that sensor disconnected and the vehicle running I got my original code for heater circuit on B1 S3 *AND* a heater circuit malfunction for B1 S2! 

I then cleared codes, disconnected the rear 02 B1 S2, guess what? Got my B1 S3 Heater Circuit Malfunction P0042 ONLY










As a final confirmation I decided it was easy enough to check resistance of the rear 02 sensor heater circuit. For anyone who doesn't know, as I didn't before I started checking these sensors, on a 4 wire 02 sensor the 2 white wires are the heater circuit, the black is ground, and the grey is the signal wire. 

Upon checking I found that the rear 02 sensor had 0 ohms or no resistance.

*To Sum This Whole Thing Up *

DON'T BELIEVE YOUR BENTLEY REPAIR MANUAL, IT'S WRONG!!! :sly:

I spoke with my buddy at Vw and their information (which is supplied by Bentley) is ALSO
wrong.

If you receive a code for B1 S3 on a BBW it's referencing the REAR/Post cat sensor. NOT the center one.

I have yet to install the correct part yet but, after the above checks I'm confident I found the reason for the issue. 

Hopefully if someone has a BBW with this code they will stumble on this post and save themselves a lot of headaches and a $195 02 sensor by checking the right one the first time.

Cheers! :laugh:


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## DaveMK123 (Mar 25, 2005)

*Happy to report*

I received a email response today from Bentley in regards to this issue and it appears they will be correcting the issue.


> From: Volkswagen - Paper
> Sent: 2011 August 1, 11:50:34
> To: [email protected]
> Subject: RE: Incorrect Volkswagne Repair Information
> ...


Link to Bentley Updated 02 Sensor listing!










Pretty awesome, big :thumbup: to Charlie and the Bentley Team for stepping up and taking the time to correct this.


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## VW 2.0 (Jun 2, 2008)

DaveMK123 said:


> I don't normally go to the forums for repair information but, after the :banghead: I've run into this code I felt it necessary to post this so no one else gets burned by the incorrect information printed by Bentley in the factory repair manual.
> 
> I was asked to take a look at a vehicle for a family friend since I'm a former Vw tech and do some work on the side out of my garage at home. The vehicle was a 2004 Jetta 2.0L with a BBW engine code.
> 
> ...






Definitely Saved me some time, After reading this I have a better understanding of where to look and how to trouble shoot this problem p0042 (B1 S3)!!! Thanks for the info


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