O² Sensor


bodhi

New member
Oops sorry, thought you could see that by my membership information. Our westy is a 1986 VW Westfalia. Has the 2.1 liter engine with digifant fuel injection sys.
 

Capt. Mike

Moderator
To access membership informaion requires entering another site and doing a member name search -- and only a couple of us have that access. The rest of the members that might respond, don't.

Reseting is fairly simply, but does require a tool as the reset button is recessed within a guard to prevent against accidental use.

If you look at the Bentley wiring diagram, 97.90 circuits 45-46, you'll see how the counter works (sort of). Most VW warning circuits are always live and complete by connecting to ground. The terminal #61 is live 12v from the alternator, which means it's only on when the engine is running. Terminal OXS comes from the live instrument panel warning light circuit. When the little odometer closes the switch, it completes the circuit to ground, and the light should come on.

If you are truly getting it reset -- and I remind you that the O² warning light comes on with ignition as part of the test circuit and only goes off once the engine is started -- then you should check the 3 components of the circuit. 12v to #61 with engine on? Good ground? The little arrow inside the CAT box is a semiconductor diode (one-way current flow switch) so that the CAT box works both ways -- in test mode and in running mode without one running into the other. Or the mechanical switch could have failed and stuck in ground mode (light on).

Unfortunately, electrical problems are usually inter-related and the only way to diagnoise for sure is the painstaking troubleshooting procedures with test light and volt-ohmeter. See "Distribution module . . ." topic for some tips; also there is a topic on electrical diagnostic tools in the TOOLS forum.
 
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mr.rocksteady

New member
well, bentley doesn't tell you much, but if you look at the picture at 90.15, then you can see the mileage counter hooked up to the speedometer cable (running to driver's side front tire). trace back from the tire and you will find it mounted to the chassis. anyhow, there is a white button, use something long and thin (golf tee worked for me) and press it all the way in. you will hear it click. thanks for a great site capt. mike. tp
 

vw-traveller

New member
Tip - wire to O2 sensor on 79 CA

What learned to today about the wiring harness wire to the 02 sensor:

For years I have had the problem that my engine has been running to rich. I replaced the 02 sensor a number of times, after not passing smog again I took it to the Buslab (www.thebuslab.com) in Berkeley. They figured out the problem. The green wire going to the o2 sensor has a shielding outer wire and a transmitting inner wire. The wire connector on mine was wrongly connected to both wires. That made the O2 sensor feedback incorrect and make the engine run too rich.
I hope this feedback will help others avoid a huge Smog headache.
 

treejay

New member
I was hoping to find some help on a question I have. I am a beginning mechanic trying to learn as much as possible. I have an '83 water cooled westy, recently with low gas mileage. Upon looking around in the engine compartment, I noticed that the wire coming out of the tailpipe before the catalytic converter wasn't connected to anything. Upon reading things on this website and in the bently (which i don't understand much), I believe I've concluded that this is part of the fuel injection system. is this the O2 sensor? If so, what is is supposed to connect to? If not, What is this wire ? Sorry if this is in the wrong message forum.
thanks.
ej
 

Capt. Mike

Moderator
Yes, the O² sensor screws into the exhaust system just ahead of the catalytic converter. Bentley diagram 26.7. It connects directly to the fuel control unit (ECU) per wiring diagram 97.55, circuit 7. The connector T1 should be in the wiring harnesses on the left side of the engine compartment. O² sensors are important to running, pollution and mileage.
 
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treejay

New member
So my oxygen sensor is indeed disconnected for one reason or another. I attempted to reconnect it yesterday, trying to use Bentley as a guide but wasn't successful, mainly for 2 reasons. 1) I am a novice to the point where I don't understand how to interpret and read the electrical diagrams provided in the Bentley to make me confident that I am performing the right task or identifying the right wires or connections. Can anybody recommend a good reference material to help me learn how to read these electrical schematics?

Secondly, I found what I believe to be where the disconnected O2 sensor should plug into. It's a green wire that is coming out of the cluster of wires from the FI control unit. The problem is that both connections have female ends, therefore incompatible. Why do they both have female ends and if it is supposed to be the correct connection, where can I by the right piece to bridge the gap? Thanks ahead of time!
ej
 

Capt. Mike

Moderator
You didn't give mileage or history but O² sensors are service items to be replace on a schedule (current ones can go 90,000 miles). O² sensors are all covered under Bosch patents and a relatively few models cover all vehicles, thus only maybe half-dozen models. The differences within models being their wiring harnesses for the particular vehicle. Generic replacements typically require splicing into the existing harnesses. You may have a replacement that will require either a new male connector, or get a female to female adapter at any electronics supply store.

The Bentley has an excellent primer on wiring pages 97.3-97.6. There is a topic on this subject in the BASIC WIRING forum as well.
 
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icarus

Moderator
First, in response to EJ: Coincidently I am working on an O2 sensor problem. The green wire coming off the sensor has a female spade lug connector. The wiring harness also has a female spade lug connector. There should be a double male spade lug between the two, (to allow the connection of the two females) Should be available anywhere, very generic.

Second, a problem with O2 sensors I have heard about is that the coax braid around the wire, especialy near the spade lug plug can fail and short to ground. Check carefully near the plugs for signs of poor coax and insulation. This can lead to very erratic running.

Finally, (for now anyway,,) I have been trying to solve an ongoing problem (described in other FI threads) The symptoms have always been poor running solved by turning the key off and quickly back on. It has always been a problem that is very intermitent and always resolved itself after a few on/off resets. Yesterday it happened again, (after a long hiatus of not doing it) and this time it wouldn't resolve. It would reset for a mile or two, and then run poorly again. After changing out the ecu, since I don't have the tools to check, doing the tests on the idle stabilizer, afm, etc, I look to the O2 sensor. After disconnecting it, I found that the continuity on the heater wires showed open. (Why does the sensor need a heater anyway?) With the sensor disconnected the car runs fine, as it tells the ecu to run in default mode. I can't difinitavly test the sensor (W/O exaust gas equipment) but I have to conclude the sensor is sending bad info, and therefore causes the engine to run rough. I still can't explain why it has been so intermitent but I think I have solved it. (of course the truth will be know after a new O2 sensor and time will tell the time.)

Now I have to get and install a new one. I have to do a complete exaust sytem, incuding cat, so I will wait and do the sensor then.

Icarus

PS. Capt. MIke, I noticed in your Feb 2002 post about 2 wire and three wire O2 sensors. The question is, what is the diminushed performace associated with a non heater sensor. My inuition says that since I drive almost exclusivly long distances, the exaust will be hot, therefore the heater would be sort of redundant. If I do use the 2 wire sensor (because it is much cheaper) how do you wire it? I assume black wire for data, white for ground, eliminating the other one. Is this correct.

Icarus
 

Capt. Mike

Moderator
None. The choice of wiring is more a function of the input to the ECU than any inherent advantage in practical use. The 2 & 3-wire units, particularly the heated units, serve to stabilize the signal and prevent the ECU from making incorrect adjustments until the unit is up to operating temperature, perhaps from overcompensating to a point of running problems or engine damage (too lean). Since this is a function of the ECU and cannot be changed, stick with factory, or its equivelent generic substitute. Now that replacement intervals have been increased to 90K mi., that's not an unreasonable interval.
 

icarus

Moderator
I've found several sources for the 3 wire sensor at under $40. The stock oem with the wire plugs are over $100. For $60 I can splice with the best of them. 3 wire it is!
 

treejay

New member
At the request of Capt. Mike, I am reposting this post, originally posted in the "Engine misses, surges or bucking (FI related only)" thread. It has helped me and another member of this site (reddeer) solve a problem that was causing major fuel consumption and bucking/surging. It was resulting from a bad connection of the O2 sensor. Here's the post:

Posted August 16, 2005 06:06 PM
1983 water cooled vanagon L

Here's something interesting that I learned today which fixed a bucking/surging, running extremely rich problem I have been having. Given that the prior poster is trying to figure out what's wrong with their van, this is one more thing you can check on the long list of things that you've already checked.

About a month ago, I realized my O2 sensor wasn't conected. I bought a new one, installed it myself. here's the rub: I striped the green wire coming out of the FI multipin connector. I didn't realize that this wire was a shielded wire with an inside core, then insulation, an outside wire, then the outside green wire. It's just like coax cable. When I striped it, I mistakenly braided the inside wire with the outter shielding wire and then spliced both to the new O2 sensor. This eventually caused all these recent problems I've been having, namely running way too rich and bucking/surging. Today, I learned that the outter wire shielding is a ground connection and this shouldn't be braided with the inner core. I peeled the outter shielding wire back, and viola = van runs great again. I find it amazing that only a couple strands of copper improperly connceted or shorting out can cause such dramatic running problems.

I hope this helps someone else somewhere. good luck

ej
 

dfresh

New member
O2 Sensor Problem

I am new to this board and am looking at buying my first Westy. I appologize if I break any of the guidlines Cappy, but I'm in a bit of a time crunch.

I'm looking at a 1988 full camper westy with about 165,000 miles and the engine was recently rebuilt. The add says that the engine floods with the O2 sensor connected but runs fine without it. I sent an email asking them to describe the problem further and if it had a the AFM harness installed and received this reply:

"When the o2 sensor is hooked up, the symptoms aren't obvious at first. It starts right up, idles, and does not die while running at idle. The first time we ran it we went 200 miles without a problem, running strong and well, and suddenly we lost power, observed black smoke from the exhaust, and the engine flooded. It would not restart. It went to the shop. the ECU unit was replaced. We ran it and the same problem occurred again. We disconnected the o2 sensor and the problem went away. We replaced the o2 sensor with one from Gowesty and the problem still happened again while connected, disappeared when disconnected. And no, an after market air flow harness, to my knowledge, has not been installed. "

2 questions:

1) any ideas on the problem? I know I've probably not provided nearly enough information to narrow it down.

2) How much damage could I do if I drove it about 1,000 miles without the O2 sensor connected?

I'm already ordered a copy of the Bentley manual but will not receive it in time. I'm going on a road trip to inspect the Westy this week, my main focus will be what kind of shape the body is in. I figure that engine problems can always be fixed(and I guess I will be learning a lot about fixing them)

Thanks for any help and again, I appologize if I screwed up on any of the guidelines. AWESOME SITE!

Thanks,

Doug
 
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Capt. Mike

Moderator
Those symptoms are very similar to the Vanagon Syndrome (own topic). The harness fix cures a multitude of problems beyond what the original tech bulletin described. Understand, the O² sensor has the effect of trying to correct the fuel-air mixture bercause it detects something amiss upstream. O² sensors are very generic and reliable; if yours has been replaced, then the problem is not likely to be the O² sensor, but an upstream problem. If the AFM sends a bad signal because it doesn't have the upgrade harness, then the ECU goes wacky and the O² sensor then detects the bad mixture and tries to send signals to correct. Each by itself is working, but if the the signal between AFM & ECU becomes unstable (what the harness corrects), it could do what you describe.

EVERY Digifant Westy should have the FACTORY AFM harness update -- period. If you drive without the O² sensor, it is supposed to default to an emergency setting that will not harm the engine, however that is not a long-term solution. It's only meant to get you home.
 
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MillBayJohn

New member
Engine Idle Fluctuates after engine warm-up

The 0² sensor detects variations in exhaust gas content and sends a correction signal to the FI control box, which then adjusts mixture. This is done on a continuing basis. Thus it is normal for an FI engine to "hunt" at idle -- change RPMs slighly up & down as the system constantly adjusts. This is a sign of a working controller & O² sensor.

However it should not hunt excessively; maybe 50 RPM or so. If it's swinging several hundred RPM, you have other more serious problem. Likewise if it changes idle RPM a large amount after warming up.

My 1985 Westy, 1.9 L idle fluctuates between 1000-1250 rhythmiclly after warm-up. My Mexican mechanic suggest I purchase an idle control valve....I not convinced after reading a number of posts that suggest that there may be a number of causes...not necessarily this valve. None of the posts I have read seem to fit my problem exactly. I included Capt Mike's reply here which suggest this gentleman could have a more serious problem....Could you give me some guidance please
 
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Capt. Mike

Moderator
The 1000-1250 idle is too high and too much of a spread for O² 'hunt', which indicates it has far more serious FI problems that are not likely to be the O² sensor.

Go to your Bentley §24.18-24.37. I'm confused as to what you are talking about -- there is no "idle control valve" in the Digijet system. There are two idle boost valves for P/S & A/C correction and there is a decel/idle SWITCH that controls the throttle valve for decel, acceleration and full throttle modes. Neither of these are O² sensor problems for this topic. Did you test the O² sensor §24.16 & 24.20? What other tests have your run and have you checked the items suggested in "idle problems" & "throttle valve" topics (Guideline #3)? Testing all of these are described in the Bentley; you don't replace parts until you've tested them to be sure that's what the problem is. Most items in the FI system can be tested with a volt-ohm meter. :cool: Is your mechanic perhaps using the wrong terms (language problem) or does he not understand the FI system and what those systems do?
 
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Hamfisted

New member
Hello out there.. I just signed up today and thought I would comiserate with the masses. I have a 1.9 '84 Westfalia, no problems (other than grossly underpowered) with a trip to Portland (about 1300 miles) and I love my Westfalia. SO.. more is better? Eh? I just bought a 1987 Syncro "AS-IS". The problem with it generally is that when I leave the house with the engine cold, it drives fine for about 4 minutes then the 'top end' performance chokes. I thought it might be the catalytic converter, I have already changed the gas filter.. it just does not operate properly (loss of power) when accelerating.. it goes 45 on the freeway with my foot all the way into it but just not right. I disconnected the O2 sensor and, well.. not bad. It seems to drive ok, but because it is new to me, I really can't properly judge. I have been looking at threads from +/- 5 years ago and am wondering if the GOWESTY HOTWIRE Solution is viable. I am prepared to replace the O2, the harness and the MAP if I have to, I am just wondering how to further whittle down the problem. Anybody with info on the DIGIFANT/HOTWIRE solution? You think it might be a bad O2 only?? The vehicle has been NON-OP for 5 years, and looked like TROLLS were living in it. I ripped out most of the carpet and hosed it out in the driveway.. freaking filthly filthy nasty dirty.

My name is Richard and I am a VWFFL (VW fan for life)
 

Capt. Mike

Moderator
Quit guessing and avoid unnecessary parts swapping. Do the diagnostics of the FI system in the Bentley (required to use site). Your symptoms are not 0² sensor. Cat converters can be checked easily and the fuel delivery system could also be suspect.
 

Hamfisted

New member
Why thank you Capt. Mike.

I have the Bentley. I have only now (today) finished the original tank of gas that I had put into it when I bought it. It took just a little of 18 gal. to fill when I got it home. I took it to a reputable shop, FRITZ&PETERS in Berkeley, they replaced the Catalytic Convertor. I have replaced the O2, purchased and installed a AFM harness ($190), new cap/rotor/plugs/wires and gas filter. Took it into the SMOG shop and it registered over 334ppm HC at idle (maximum is 150ppm). Now, a couple of things, first off.. the technician was unable to get the engine to stay under 1000rpm to run the test and he took liberties in turning what appears to be an adjustment screw in the manifold near the accellerator cable. That brought down the idle to about 987rpm for testing purposes. The second issue is/was that when I took it in for the test, the gas tank was down to the last gallon or so of fuel with the fuel jet cleaner (a can of KRAGEN or generic jet cleaner) that I forgot to thin out by topping off the tank with fresh fuel.

So.. I am now on page 24.51 and 24.47 wondering how to adjust the idle by alternating between the idle adjusting screw and the CO adjusting screw without having the equipment to monitor the CO content. I am supposing that I am going to have to bring it back to the shop to have the settings renewed. That friggin BENTLEY is a monster of a book.

Let you know what I find out.. California Emission Testing is designed to get all older vehicles off the road (seems that they think that purchasing an electric car is the solution) to make way for the HYDROGEN vehicles that the Govenor wants. In my personal estimation, this vehicle is running fine considering it has not been on the road for over 5 years.. but I am just now comming to the conclusion that the previous owner probably threw his hat in 5 years ago. What a pain.
 

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