81 SC Oxygen Sensor Relay - Page 2

MarcoPau · 04-04-2012, 04:34 AM

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

psalt · 04-04-2012, 07:45 AM

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.

MarcoPau · 04-04-2012, 02:28 PM

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

psalt · 04-04-2012, 02:35 PM

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.

Peter Zimmermann · 03:00 PM

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?

MarcoPau · 04-04-2012, 03:19 PM

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

MarcoPau · 04-05-2012, 03:18 AM

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 Lamba relay questions 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!

MarcoPau · 04-17-2012, 12:03 AM

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

ipacketeer · ipacketeer's Garage

MarcoPau,

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

MarcoPau · 04-22-2012, 01:34 PM

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!

ipacketeer · ipacketeer's Garage

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

Cliff Beer · 06-12-2013, 01:07 PM

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.

john walker's workshop · 06-12-2013, 02:00 PM

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

Cliff Beer · 06-12-2013, 02:58 PM

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

john walker's workshop · 06-12-2013, 04:10 PM

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

Porchdog · 05:22 PM

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

Bauba01 · 08-31-2015, 01:55 PM

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.

Bauba01 · 08-31-2015, 02:48 PM

john walker's workshop · 08-31-2015, 05:10 PM

Ya think? That's the power wire.

Bauba01 · 09-01-2015, 01:36 PM

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?