Used dielectric grease on O2 sensors -- Uh oh.

[mlnnc]

How can I thoroughly and successfully clean dielectric grease from the O2 connectors?

Thinking I was doing a good thing I used dielectric grease on my O2 connectors. Oops. I've confirmed what I now recall having heard before but always discounted -- that the O2s actually use the little bit of air that can make its way down the wires from the connectors, traveling between the copper and the insulation. Amazing, but so I now learn, true.

I tried cleaning the connectors with electrical contact cleaner. Repeatedly. Still no luck. The truck starts and runs seemingly well, but the UltraGauge shows short-term fuel trim of +25, indicating the ECM is getting no signal from the sensors and interprets it as a lean condition. But because the voltage is zero or near zero, the ECM gives up after a minute or two, shows STFT at 0.00, goes into open loop and throws the P0130 and P0150 codes.

So today I installed two new Bosch 15175 O2s and took the truck for a test drive. Success!

Or so I thought. The fuel trims looked normal on the mile and a half test drive, but when I left to meet a friend a half hour or so later they were back to +25, then 0.00 STFT, open loop, codes, SES light, yada, yada, yada. (BTW I know I could set up the UG to read O2 voltage directly, but I think the +25 STFT clearly tells the story).

I've again disconnected the connectors and sprayed liberally with contact cleaner. The new sensors were obviously clean when installed, but there must have been just enough grease still in or on the harness-side connector to contaminate the connectors on the new sensors.

I'll reconnect and drive the truck either later tonight or tomorrow and see what happens, but in the meantime does anyone have any other ideas to try? I REALLY don't want to have to replace the harness-side connectors.

 

[K-rover]

I was never able to get my harness side connector clean. I eventually just spliced a new connector. It wasnt that hard to do from the top of the engine. Good luck.

 

[ERover82]

that the O2s actually use the little bit of air that can make its way down the wires from the connectors, traveling between the copper and the insulation

wat ?

 

[fishEH]

Found this from Tom on LRF.

If the DII are zirconia sensors then no, do not use anything on them.
I was wondering about this myself and talked to an engineer at NTK, this is what he told me:
Titanium sensor - ok to use dielectric grease on the electrical connector
Zirconia sensor - uses reference oxygen pulled in through connector, so not ok to use dielectric grease

I don't know for sure, but I'm guessing the DII is Zirconia as that's the newer technology.

​​​​​​​

 

[mlnnc]

wat ?

Yeah, that's what I thought, but here's the statement.

"... but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It's hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air).
​

And here's the source. Second paragraph in the "How it Works" section.

http://www.autotap.com/techlibrary/understanding_oxygen_sensors.asp​

 

[mlnnc]

I was never able to get my harness side connector clean. I eventually just spliced a new connector. It wasnt that hard to do from the top of the engine. Good luck.

How did you do the splices? Solder and heat shrink or something else?

Accessing them to do that job looks like a real PITA to me. I suppose, however, that if I got the longest possible runs of wiring from the donor truck(s) it could make future swaps easier, at least a little bit.

 

[ERover82]

Chemtool and compressed air?

 

[mlnnc]

Chemtool and compressed air?

Huh? Mi no comprende. So ... soak them and then blow with compressed air. Hmm ... I do have an air compessor ...

 

[ERover82]

If there's grease in the connector then use a strong solvent like chemtool (wear gloves), and compressed air to blow it through the connector and cable, from both ends if possible.

 

[K-rover]

How did you do the splices? Solder and heat shrink or something else?

Accessing them to do that job looks like a real PITA to me. I suppose, however, that if I got the longest possible runs of wiring from the donor truck(s) it could make future swaps easier, at least a little bit.

I removed the clip holding the connector, then followed the wiring up to behind the intake up by the coil packs. Then pulled the connector up and did crimp splices with heat shrink over that then put some of that split loom over all that.

 

[mlnnc]

How do I test continuity from the O2 sensor connectors to the ECM? I know how to test continuity when I can connect the leads from my multimeter to both ends of the circuit to be tested but the leads are not long enough to reach from the connectors in the engine bay to the ECM behind the passenger-side kick panel.

OR

Do I just need to buy a pair of extra-long test leads?

I'm asking because I'm becoming convinced the problem is not grease in the connectors. I'm beginning to believe it may be a problem with the ECM because, as I said in my original post, the system worked fine after I installed two new O2 a few days ago, and then failed when I drove the truck again later that hour. I've since carefully cleaned the connectors at least twice (although not yet with Chemtool) and had no luck. It makes little sense to me that the system would work fine once with new sensors and would then fail on both sides at the same time.

Thoughts?

 

[KyleT]

Never heard of the air seep before or that website...

 

[helievacpilot]

Found this. See #2.

http://densoautoparts.com/oxygen-af-sensors/oxygen-sensors

Seems to me though that the "seeping" air would be from outside of the insulation, in-between the individual wires, or why would it need to be porous?

I've used dialectric grease on every O2 sensor I've ever replaced and never had an issue.

 

[mlnnc]

I've used dialectric grease on every O2 sensor I've ever replaced and never had an issue.

How do you use to apply dielectric grease to the O2 connectors? Do you apply it in the space between the outer shell and the inner, white plastic where the actual copper connectors are mounted, or do you apply it directly in the four connector cavities? Thanks.

 

[helievacpilot]

How do you use to apply dielectric grease to the O2 connectors? Do you apply it in the space between the outer shell and the inner, white plastic where the actual copper connectors are mounted, or do you apply it directly in the four connector cavities? Thanks.

Just put a small dab right over the cavities.

 

[number9]

Just put a small dab right over the cavities.

Good recommendation particularly for O2 sensors. Typically the small amount of DG dabbed over the socket cavities will coat both socket and pin enough when connected.

Usually OK to slather DG and fill connector housings on other circuits where moisture may be more common.

Would recommend using Dow Corning Electrical Insulating Compound, DC4 or DC5 as it's normally same price or less than others.
......

 

[mlnnc]

I had to step away from this problem for a couple days, partly for my mental health, but this morning I changed the Ultra Gauge setup to watch the O2 voltages directly and took the truck for a short drive. I did so because the P0130 and P0150 codes are for stoichiometric ratio out of range, not for no activity. No activity would be P0134 and P0154.

Sure enough, both sensors were showing output. Bank 2 was consistently low (0.00 to ~0.30 volts) and quickly triggered open loop, but surprisingly Bank 1 was switching normally. For the first 3 miles. It was weird to see the Bank 1 voltage drop after being just fine the first three miles.

I'm stumped, for now. I don't see how it can be a continuity problem in the harness; if it were that I'd think there'd be no voltage at all. And as I wrote in my post at the beginning of this thread everything was fine on the first test drive a week ago when I installed two brand new O2s. I have two more now on order but I'm concerned the same thing will happen again when I install them this weekend.

Further ideas welcomed. Thanks.

 

[mlnnc]

I'll spare y'all most of the gory details from the last two weeks but I think my truck's problem is solved. Mostly.

After installing a different pair of new sensors the problem persisted, although on Bank 2 only. I had bench tested both new sensors out of the boxes with a propane torch and both were switching normally. I bench tested the Bank 2 sensor again after the test drive and it failed the test. What could have caused an O2 to fail so quickly?

I stepped away from the truck again for a couple weeks, partly because I had other things going on but also because I was again stumped.

Yesterday I retested the failed sensor and to my surprise it tested fine so I reinstalled it and went driving. I had three trips yesterday and got no codes. STFTs were fine too, but I'd setup the UG to show O2 volts as well as fuel trims. I noticed that Bank 1 volts were switching normally but Bank 2 was switching more slowly. By that I mean it would read ~0.65 volts for 30 seconds or so and then drop low to ~0.20 volts for another 30 seconds. That continued back and forth all day, but Bank 2 STFT was switching normally.

So this morning I swapped the sensors side to side and took it for a drive. Just like yesterday Bank 1 volts were switching normally but Bank 2 was again slow. That left me scratching my head. Why would Bank 2 switch slowly if it isn't the sensor?

At this point I think I'll leave well enough alone for now and see what happens since it's not throwing codes and STFTs are good. The truck will be driven more later this week - stay tuned.

 

[mlnnc]

Okay, time to wrap up this thread.

I still don't know why or how a new sensor appeared to fail right away and then worked fine a few days later. Maybe the sensor was fine all the time and it was a matter of adaptive values adjusting over time. Who knows.

But the final matter of Bank 2 switching much more slowly than Bank 1 turned out to be "pilot error."

The truck gets driven only occasionally these days. Every time I drove it over the last four weeks it ran fine, fuel trims looked great, and there were no codes or pending codes, but Bank 2 O2 volts continued to switch more slowly than Bank 1.

Then when out for a drive yesterday I happened to look more closely at the Ultra Gauge. I finally noticed that in my hurry to set up the O2 voltage displays I'd set up the DOWNSTREAM O2 for Bank 2!

I corrected that error and I am happy to report that both sides are switching normally! All is well.

Moral of the story? Haste makes waste, I suppose. That and double-check your work, and make sure the tool being used to measure something is being used correctly.