I need to splice the pigtail connectors from my old O2 sensors onto the new O2 sensors since the new connectors have a different shape.

As the sensor is right behind the engine and will experience high temperatures, I want to know whether regular 60/40 solder will hold up.

4 Answers 4


It should hold up. It melts at around twice the temperature where water boils, which I don't think you'll ever experience in the engine bay (unless it's touching the exhaust). But the greasiness in the engine may make for a poor adhesion.

BTW: I am one of those people who would rather crimp than solder.

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    @Zaid ... ensure you utilize heat shrink to seal it up and you shouldn't have a problem. You would have to have a constant temperature of just over 400 degF for it to melt. It would have to be touching the exhaust directly to achieve that temperature, then with the addition of the heat shrink there should be no issues at all. Feb 9, 2015 at 11:14
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    @Paulster2, if the heatshrink touched the exhaust it wouldn't last very long. I'd solder clean, freshly-stripped wires, cover them in heatshrink and strap them out of the way.
    – Chris H
    Feb 9, 2015 at 11:23
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    @ChrisH ... You are right ... I was just assuming this would be done in the first place. You'd never leave any wires to touch the exhaust, whether soldered, O2 wires, or what have you. Just not good wrenching practice. Feb 9, 2015 at 11:27
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    @Paulster2, exactly, though I tend to state these things explicitly on the assumption of a naive reader. And not just the exhaust, always strap up the wires IMO.
    – Chris H
    Feb 9, 2015 at 11:29
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    In addition to heat shrink, I recommend wrapping the repair in the split corrugated plastic tube that is often used for wiring. It serves two purposes, and with a soldering job you need both. א) it protects from the highest heat. ב) It keeps the repair warm after the engine has been shut down. Thus, if the engine is restarted in a few minutes it prevents thermal cycling the joint, which weakens it. Better to stay a little warm then warm, cool, warm, cool.
    – dotancohen
    Feb 9, 2015 at 14:36

Solder (60/40) or any other lead-based sort has little mechanical strength. And it decreases as heat goes up. Furthermore, some of the wires used in various places don't work very well with field soldering (such as Litz wire). On the other hand many of them don't work well with mechanical fastening, ie, crimping. Depending on the wires you're working with, I'd prefer to crimp, solder, and maybe even use a heat resistant wire nut on top of it all. And I would be certain to strain relief the join, so vibration won't cause a mechanical stress or strain and pull the joint apart.

Sometimes it makes sense to (more or less) braze a connection in the case of something whose environment is quite hot (ie, near exhaust manifolds).

But you haven't said which sort of engine you have -- I'm merely assuming it's some sort of gasoline automotive engine.

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    Mechanical strength shouldn't be much of a concern here as the wires will not flex significantly during operation.
    – Zaid
    Feb 9, 2015 at 18:22
  • Non gasoline engines don't have O2 sensors, I think, since the O2 sensors are for detecting the mixture of gas and oxygen.
    – TylerH
    Feb 9, 2015 at 22:01
  • @TylerH ... O2 sensors only check oxygen content. Some of the newer diesel engines utilize an O2 sensor, so not strictly for gasoline use anymore, either. Feb 10, 2015 at 13:02

Yes it will be fine...if you correctly solder it. If you dont know how to solder then i would suggest a crimp.


Always crimp.

In fact, the O2 sensor relies on a small amount of air (O2) passing down the wires in between the gaps in the individual copper strands to allow proper operation of the electrochemical cell.

If you solder, flux may block off this path to the cell, and cause the O2 sensor to stop working. It will not be damaged, but will not operate correctly. Normal operation can be resumed by unblocking the gas path down the wire. (O2)

All kits will be provided with crimps for this reason.

Dead thread, I know, but this is important for future searchers.

  • An oxygen sensor works by converting the difference in oxygen levels between exhaust and ambient to a voltage. The voltage potential is carried by conductors which should have low resistance. Oxygen plays absolutely no part in the quality of the voltage signal on these wires. Gas does not travel on wires. This is absolutely not a valid answer.
    – SteveRacer
    Jul 27, 2016 at 7:39
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    @SteveRacer Don't be so hasty on that. Zirconia sensors do receive an external oxygen reference through the wiring and in theory it's possible to obstruct it. At least that's what I learned, do correct me if I'm wrong. And soldering might be a bad idea anyways because of the galvanic effect affecting the voltage output. Jul 27, 2016 at 7:46
  • I'll retract my comment. I am not advocating soldering O2 connections, but I believe the reason is changing the resistance on the wiring on a very sensitive signal, not a bit of flux blocking oxygen permeation in the harness at one particular point. Oxygen doesn't flow through conductors. It might flow around an in between them, but one solder connection doesn't clog the pipe. The wiring I've seen defies soldering in most cases anyway.
    – SteveRacer
    Jul 27, 2016 at 8:11
  • It seems I'm just plain wrong. Older sensors have a port; newer sensors advocate not even using dielectric grease on the connector because it might interfere with reference flow.
    – SteveRacer
    Jul 27, 2016 at 8:22

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