02 Sensor Heating Problem

[Don Plumley]

Hi,

On my 993 I have OBD Codes P1117 and P1121: O2 sensor heating not working after the cat on both banks. These sensors were disconnected for cat bypass pipes and hung open under the engine. They were fairly black, unlike the sensors in the cat pipes that were grey.

I've reinstalled the cat and reinstalled the sensors. Atfter 23 miles the CEL comes on. I've reset it twice, and today I read the codes. Could it be that by being in the open for so long, the sensors are broken? Is there anything else I should look at?

Thanks, and Happy Porsche New Year!

Don

(I posted this on Rennlist, but more Pelicans seem to be online now)

[RickM]

Don,

Did the code come up after they were disconnected? If so, were they exposed to the elements...water and dirt?

To add:


* DO NOTdrop or use an oxygen sensor that has been dropped as this may have caused shock damage to the ceramic element

* DO NOT use any compounds on or around the sensor unless labeled as oxygen sensor friendly products

* DO NOT use impact wrench or conventional socket type wrench to install sensor

* DO NOT allow sensor or lead wire to touch exhaust manifold or any other hot component

* DO NOT expose this product to water, oil, windshield cleaner, anti-corrosion oil, grease, terminal cleaner, etc.

* DO NOT use leaded fuels, silicone or metal based additives

* DO NOT store under high humidity conditions

[ischmitz]

Hm, if they were exposed to the elements when driving around I think they are toast.....

[Don Plumley]

They were hanging by the bypass pipes, tied up to a nearby support. They were open to the world, and as I mentioned, pretty grimey.

They reported the heater error while out in the open, as well as after back in the cat and 100 miles later.

One of the sensors had bits of ceramic coming out of it. Thought it was a pine needle, was a small toasted bit of ceramic. I presumed this indicated its demise, but thought they were more durable than that.

Now to find a pair of "slightly used" O2 sensors - any leads?

Thanks guys!

Don

[RickM]

Don, go with Bosch generics. You'll have to splice the connectors from your old ones with the Bosch supplied kit but you'll save quite a bit. I did this on all four sensors for a TT earlier this year and they're still working perfectly.


What year is your 993 ? C2? I'll bet the Bosch part number for the generic is 15738.

[ischmitz]

Did the same and it worked for me so far. While a "used" sensor might still work their aging mechanism is that they get slow due to continous poisoning of the active element. Their response times to O2 concentration changes lengthen until the DME's feedback loop eventually gets confused. That's when it starts to throw up the CEL and fault codes.

Ingo

[Don Plumley]

It's a 96. But a DE/TT car and I'm very likely to remove the cat and put the bypass pipes back on after I pass smog. So I'll disconnect the sensors and save them for each two year interval.

I agree with the generics. I seem to remember with older O2 sensors the wire was important and mucking with it was a recipe for disaster. But I'll either find someone who has just installed a bypass pipe in a no Smog state or get some cheap generics online.

Thanks again guys. Happy New Year (now off to Dinner!).

Don

[RickM]

Good deal...just keep the original sheaths and boxes to store the sensors in. Good luck. Oh and 15738 it is...for all four.

[Bill Verburg]

Originally posted by Don Plumley
It's a 96. But a DE/TT car and I'm very likely to remove the cat and put the bypass pipes back on after I pass smog. So I'll disconnect the sensors and save them for each two year interval.

I agree with the generics. I seem to remember with older O2 sensors the wire was important and mucking with it was a recipe for disaster. But I'll either find someone who has just installed a bypass pipe in a no Smog state or get some cheap generics online.

Thanks again guys. Happy New Year (now off to Dinner!).

Don

there was a thread where someone claimed that the wire was used to transport gas to the sensor for the reference signal.

This is nonsense!

If using a generic where the wires must be spliced just be sure to get a soild sealed joint.

The reference signal is generated by the difference in O conent between atmosphere and in the exhaust pipe. As Ingo said w/ age this signal degrades, in addition any exposure to silicone or silicone vapor(think innocuous stuff like vinyl dressing) will cause sensor failure in short order.

However the heating element is sealed and will only be crippled by cracked ceramic case or other mechanical internal separation of the wire.

If they were exposed to environmental insult beneath the car they are likely toast. The usual strategy is to get them into the engine compartment and shield them from mechanical and chemical(silicone) damage

[RickM]

Originally posted by Bill Verburg
[B]

If using a generic where the wires must be spliced just be sure to get a soild sealed joint.

/B]

The splice kit that comes with the sensor is very well designed. If the near fool proof instructions are followed the connection should be fine.

(...and I'm the type that usually opts for solder joints)

[Don Plumley]

It's all making sense now (assuming the sensors are failed and not the heater circuits).

After I source the Sensors, I'll have to come up with a clever way to protect them in the engine compartment. And it is making sense to go ahead and buy new sensors, put those into the pre-cat circuit since that provides fuel mixture input, and use the working ones for the post-cat.

Ingo / Bill / Rick - many thanks for your help on this one.