Quote:
Originally Posted by wazzz
I'm curious to read the explanation for this. I've read some weird theories about the reference air being measured through the wire strands hence needing to be not soldered but crimped to preserve wire strands. 
But I've also read that this is kind of urban legend. And the O2 sensor wire is soldered inside the ECU anyway.
So, BS or real technical justification? |
Chat GPT gives a perfect answer and it’s English is far better than mine :-) :
Question:
Why should the wires of an ox sensor of a car being crimped and not being soldered? Something to do with reference air throughout the wire?
Answer:
Yes, the reason is not about normal electrical conductivity, but about the oxygen sensor’s design and how it “breathes.”
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🔑 Key points
1. Most zirconia O₂ sensors need a reference to outside air.
• A narrowband or wideband oxygen sensor compares the oxygen in the exhaust with oxygen from outside air.
• Many sensors draw that reference air through the wire insulation and the crimped terminals, not through a visible vent hole.
2. The wire and terminal are designed to be slightly gas-permeable.
• The sensor’s lead wires are usually special “porous” or “vented” insulation.
• The factory crimp connection keeps electrical contact but still allows a small path for air diffusion.
3. Solder blocks the air path and can damage the sensor.
• When you solder, molten solder wicks up the strands and seals the conductor, stopping air flow.
• Heat from soldering can also damage the wire’s gas-permeable insulation and wick flux or solder inside, ruining the tiny vent path.
4. Crimping avoids heat and keeps the designed micro-vent.
• Proper OEM-style crimp terminals keep the mechanical and electrical connection while leaving the tiny air diffusion path intact.
• That’s why all sensor makers (Bosch, Denso, NTK, etc.) say: don’t solder O₂ sensor wires.
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🚗 Bottom line
• Crimp = good → keeps the oxygen sensor’s reference air path and proper electrical connection.
• Solder = bad → can seal the vent path, overheat or contaminate the sensor lead, and cause inaccurate readings or premature failure.
If you must repair an O₂ sensor harness, use proper crimp butt connectors or OEM pigtails (sometimes with heat-shrink that still lets the wire breathe).