81 SC Oxygen Sensor Relay
 

I have a question regarding the Oxygen Sensor Relay (under the passenger's seat) on my 81 SC. What are the indications that the relay is not working? My SC started suddenly misbehaving recently. On the morning in question, it fired up fine and all was normal. Halfway through my trip to work I noticed some slight hesitation when accelerating. Along with this hesitation, I discovered that my A/F meter was reading nothing… Now when I crank it up, it starts and idles fine but burps and spits when the accelerator is slightly depressed.

Years ago, I tried replacing this relay with a regular one at an automotive shop and discovered first-hand that all relays are not created equal. I promptly reinstalled the original relay. As my memory serves me, my car behaved almost the same back then with the wrong relay as it is now with the right (but old) relay. Is this a sign that my real Bosch relay is no lower operating properly?

Any help will be appreciated as I do not want to start randomly buying parts without knowing if this is a possible culprit.

I found that replacing the relay with something from the store made me question the quality. I had an 83 that I thought the warm up regulator was going bad, after replacing it still was bad, a friend showed me the error of my ways and replaced the relay from the store, worked long enough to make me think it was working aqnd went south again. The original relay is VW marked, went to VW and they couldnt find it so I ordered new from dealer.
Relatively inexpensive, problem solved
If you still have problems, start at the fuse board checking the system.
Bruce

Daryl,

Do yourself a favor and learn how to hook up a dwell meter to the lambda test port. The Bosch CIS lambda will talk to you, all you have to do is listen. It will tell you immediately if the system is working , and give you a proxy for the mixture, allowing you to make intelligent adjustments. All you need to know is available by searching this site.

I have had the relay go bad and car was under no way able to drive , it would start rough but you could not drive. I found the relay was bad and went to my local Napa for a replacement. The Napa relay worked like a champ and I did not think much of it till trying to diagnose a small cold start issue. I have all components of my CIS working and within spec. I was chasing a small problem to make perfect and I thought maybe the Napa relay could be the issue. I ordered the stock relay and found it was 100% the same as the Napa as far as every CIS test that could be run.

just unplug the relay and see if the idle gets all wierd. if nothing changes, then it's not working. it gets power from the domelight fuse, so if the domelights work, no need to check the fuse. you can also pull the fuse to check.

A quick follow up question... I ordered a new Oxygen Sensor Relay from our host and installed it this morning. Replacing this component certainly corrected the issue but oddly the car seemed to run much better than before the misbehaving started. I was under the impression that the relay's operation consists of either on or off (continuity or no continuity). Is it possible for a relay's performance to degrade while still operating properly?

It is possible that not having driven the car for three weeks could have made it seem more responsive, quicker revving, and stronger. However, the car was truly a much more enhanced tiger and the change was too dramatic for me to actually believe that this 'forgetting' theory is accurate.

No, I think it is your imagination. Now that you think you have fixed the problem, my advice would be to actually test the system and see if it is functioning correctly. Fifteen minutes with a dwell meter will give better results than speculative theories.

I have experienced first-hand, on more than one occasion, what you experienced. Relay replacement can feel like you've given a car 30 hp + a smooth pill. When the relay fails the car will cold-start poorly, and run badly through its warm up cycle. When the car reaches full temp it can "feel" almost normal, but after a cool down the same running issues occur. Glad it's fixed!

Just wanted to add to this discussion for others in the future.

Yesterday I had a strange cold start issue. It was running really lean, rough and the idle was low. Not driveable.

I pulled my air filter and lifted up on the sensor plate. Strangely the car recovered and immediately acted normal. I just figured that my sensor plate was getting sticky and wasn't able to lift enough to richen the mixture during the cold start.

So I drive off and everything is perfectly normal. About 20 minutes later (in a SHADY part of town) my idle dropped like a rock at a stoplight. I limped off of the road and into a parking lot. The car was again running VERY lean. Spitting, popping and not driveable.

After talking to a local Pelican on the phone I swapped my 02 sensor relay (always carry a spare). Car ran perfectly after that. I drove it at least 60 miles today and it was flawless - including the cold start.

Now for my question ... how do I remove the orginal relay from under the seat? I am not familiar with how it is attached to the bracket - don't see any way to remove it. Tips anyone?

mca,

Just pull it off like any other relay, it may be stiff so give it tug.

It is mounted to a bracket. Can't just pull it off.

the one attached to the bracket is a enrichment module for very cold days,(82-83 only. the 02 relay is usually just loose next to the ecm

The relay on the bracket is the one I replaced. Had same part number as the o2 sensor relay : 821-951-253.

I don't have any other relay under the seat.

its not really a relay, but kind of looks like one. its an 82-83 only fuel enrichment gizmo that works of the secondary temp switch by the oil press switch/breather area. it is attached directly to the ecm, or is supposed to be.

After further investigation I discovered that the original relay has a clip on it. It slips over a bracket next to the ECU. Initially I thought that it was permanently attached to the bracket.

http://forums.pelicanparts.com/uploa...1268000457.jpg

http://forums.pelicanparts.com/uploa...1268000472.jpg


I also firmly believe that these relays don't always fail suddenly. In my case, the relay failed over a period of weeks (and possibly months). How can this be? Intermittent connection failure?

I am also convinced that my car gained some serious boost with the new relay. Call me crazy but I rebuilt this engine 9k miles ago and I know it well. I have never felt it pull so hard through the entire rpm range. It was actually kind of scary today.

poor contacts = voltage loss. end result is the freq valve works, but poorly.

Hi, resuming this old thread cause I have the same issues of popping and spitting on my SC, plus, I noticed I have some malfunctioning on my dome light, thus hope I got to the point. I just don't understand where this relay is to be found. Can you guys help? Will take the dome light apart and clean the contacts in the meantime...

Thanks!

SC with lambda........
 

Marco,

What year is your SC? This relay (OXS) is for late SC's with lambda. The early SC's ('78-'79) don't have this relay and no OXS. Keep us posted.

Tony

Mine is 1982, and I have the lambda system. I'm checking underneath the right seat and see if I find this one relay. As far as I understood, all I can do in order to test it is unplug it when the engine is idleing and see if runs badly.

John Walker once said "hook the jumper to power with key on only, if you have to drive it until you get a decent relay". Can you maybe explain what this means, just in case I (hopefully!) find out the relay is the problem? I just bought my SC last week and I really look damn forward to have it run smoothly ;-) I guess I'll check the O2 sensor too: is it correct to get a volmeter and attach the red cable to the sensor's wire and the black cable to ground and see if the voltage fluctuates between ~0.2 and 0.8 V?

BTW, I saw the famous dome light smoking the other day, thus I assume there's really something not working around there, let me go and check...

Thanks a lot!

O my Gosh, the stupid relay... just touched #30 with #87 and #87b and the freq. valve started buzzing. Idleing jumped higher in revs and engine runs amazingly, something I didn't have the chance to know in my first P week :-)

Will be connecting the wires to power with key on only till I get a new relay.

Thanks to everybody!

Quite hard to find the relay here in Italy, guess I should buy it from the US. But, I opened up the relay and it doesn't seem to be defective, maybe only one of the pins has lost continuity with the coil, thus I resoldered it. Plugged the relay in with no shell, but it's not clicking. If I make it click by hand the frequency valve will start working and the car will run nicely. I don't know how it works, but if the O2 sensor is supposed to make it click, then is possibly the O2 sensor the defective part?

Do you guys maybe have a wiring of the sensor, so that I can check everything else is ok?

Thanks again
http://forums.pelicanparts.com/uploa...1333542844.jpg

I don't know how it works, but if the O2 sensor is supposed to make it click, then is possibly the O2 sensor the defective part?


No, the relay powers the ECU, it does not know about the O2 sensor condition. The ECU pulses the FV at one of the default duty cycles to regulate the lower chamber pressure in the FD. If the ECU is not powered, the FV doesn't pulse, and the mixture is way too lean everywhere and the engine runs poorly. No amount of bodging the mixture screw can correct the mixture across the range. Once the engine warms up, if and only if the O2 sensor is sending a signal in range, the system goes into closed loop and dithers the mixture around stoich. If the sensor is unplugged or defective, the system ignores it and continues to pulse the FV at the default value. The system ignores the O2 sensor in a cold start , cold running and in throttle positions above 35%. It is irrelevant to WOT performance, but very significant to fuel consumption, emissions and engine life. My advice is to stop playing around with the relay and replace it before you damage the ECU. There may be a reason why it failed besides age. It is a Bosch part and should be available near you. There is a test port in the engine compartment and the lambda system will tell you what is going on while it is running. You only have to listen.

The moral of the story is: replace the relay?

May I ask you what ECU and FD mean?

I will try thru electronic parts dealers I suppose, before ordering from the US. Do you think I may have a good chance of finding the relay? Are those general electronic parts?

Thanks alot psalt

Yes,

Bring the relay to an auto parts store, after all, it was made in Germany, not the US.

ECU= Electronic Control Unit (under the passenger seat), FD= Fuel Distributor ( the thing the injectors are hooked up to).

Try searching and reading the posts on "CIS lambda" on this site.

Marco, check the picture - the relay might be available from VW using the number shown. (I have always bought this relay from a P-car dealer using the 821... number.) Have you repaired your interior light problem and verified fuse condition?

http://forums.pelicanparts.com/uploa...1268000472.jpg

Yes Peter, dome light is repaired and fuse is ok, I will try getting hold of the relay thru local stores then.......... are you PZ the German actor?!

Tschuess

I went thru general parts dealers but their relays didn't have the diode (or whatever that is) between #85 and #86, thus I stopped by VW and they gave me a 4 pin relay, which has same part code of our old ones.

As I read in this old post http://forums.pelicanparts.com/porsche-911-technical-forum/193109-lamba-relay-questions.html we could just jumper #87 and #87b on the plug and use the 4 pin relay. Can you confirm this?

These are the pictures of what I just bought. Thanks again!
http://forums.pelicanparts.com/uploa...1333624638.jpg
http://forums.pelicanparts.com/uploa...1333624652.jpg

Has anybody bought the Bosch relay from Pelican or other stores? I can't find the Bosch code here in Italy, on the internet it appears as PCG 951 253 00 M14 but that's not a Bosch code (they're supposed to be 10 digits according to Bosch dealer).

Thanks guys

MarcoPau,

I believe the Bosch Code you are looking for is 0 332 019 150 , hope this will help you to solve the problem.

If you confirm this Bosch part is properly working on our SC's, that's the part I found here too. I just couldn't be sure the relay is okay cause I never had a working original relay before and don't know how the car is supposed to behave.

If that's ok, I finally got hold of it at the price of 9 euro and now can go on with the works on my Porsche :-)

Thanks!

If rest of the CIS components in working order this relay will work on your car.

So, has anybody actually found where to order the correct relay 821951253 ??

I'm hoping somebody has found where the correct relay is available...not some substitute relay which may, or may not, work.

Thanks.

here are two relays that look the same but only the one on the right will work the O2 system. notice the two 87 terminals. the left one only contacts one terminal when activated, and the right one does both. bosch # 0332019150

http://forums.pelicanparts.com/uploa...1371074344.jpg

Thanks John, that's a good point. The "Bosch replacement" for the original that I bought a while back didn't work for that very reason (both 87's were not contacted).

One responsive comment, the diagram on the side of the original 821951253 shows both a resistor and a coil between 85 and 86. I'm not sure if the resistor is essential but it may be, right?

I did just get lucky and found an original 821951253 from an online supplier. It was almost a $100 bucks unfortunately, but it's the original VW/audi relay in the aluminum housing with the right numbers and diagram on it at least.

Thanks

without a resistor, 12V would fry that spool of super thin wire.

I just got one of these from our host. It shows the two 87 terminals connected like the relay on the right above, but also shows what I think is a diode between 85 and 86 as well as the coil.

Bosch part # 0-332-019-109

http://forums.pelicanparts.com/uploa...1441057947.jpg

So as I was hoping it looks like my relay is fried, not even sure how the dome lights were working.

I replaced the relay and also saw that the red wire in the harness had come undone, I notice the prong on my old relay that goes to this wire was missing. Should this wire be connected?

Thank you.

Ya think? That's the power wire.

That prong doesn't look like it was used for a while. Cleaned the harness out and found no connector so I added it to the wire, fed it into the harness and hooked it up.

Still having idle surge when I first start.

While down there I found this little guy. When I shake it I can hear loose parts moving around. Found out it's the Fuel Enrichment Control Unit Relay. I'm going to replace it but couldnt find much info on it. Could this be causing my idle surge?http://forums.pelicanparts.com/uploa...1441143410.jpg