Hello, I had a question regarding the o2 sensor harness. specifically the driver side upstream sensor harness side. What is involved in say replacing that harness? Reason im asking, a few weeks ago i ripped the connector off on the harness side by mistake as the connector was melted and i pulled a little too hard pulling the o2 sensor side connector and the harness side connector too. So i took a replacement connector off a junkyard ls430 and used solder wraps to repair it as its in a tight spot between the firewall and engine. but im still getting a p0031 engine light code. i want to rule out the repair job but i did take it to a mechanic and he states the connector is reading and is saying 20 ohms for the heater resistance is being shown and recommends the sensor to be replaced, i took the sensor off and tested it myself at the plug on the sensor and its showing 17.5 along with 3 other sensors i checked at the auto part store. all denso 234-4138. but back to the main issue, what is involved with replacing that harness? i tried fishing around with my hand behind the engine along the harness and it snakes around everywhere and i feel its the entire engine harness that needs to be replaced. is that true or is there a section i can replace only? i sadly cant throw money at it right now as im in college and its my only car so it cant be down for too long, it originally was being replaced cause of a p0031 code and being it has nearly 190k miles it is worn out most likely and i changed many of them before.

ps: sorry if this is a duplicate post, my internet went out as i was typing my original thread and i dont think it went through as i dont see the thread. plus missing alot more info.

 

I don't think there is a separate, removable section of harness for the O2 sensors. Could be wrong. See here (don't buy from this site, reference only)
https://www.lexuspartsnow.com/parts-...ing_clamp.html

That's a very specific code I'd say you still have a connection problem. I don't have any experience with your LS someone with more knowledge can tell you were exactly the heater circuit goes and how it gets power that way you can test wiring from power source to the sensor.

 

my main concern is and i heard it a few times now that the solder is messing with the resistance. but i dont know if i can also take the mechanics word for it either, i wish i had my own scan tool to find out what its actually reading and doing. but he said it was working and reading values. i would also assume its reading values as my mpg hasnt sunk at all and actually is getting slightly better mpg than when i had the original sensor in place and more peppy. if it was a complete failure i would assume it goes into a failsafe mode and lets the engine run rich but doesnt seem to be doing that here. funny thing is when i was testing the sensor resistance values. the denso ones all had 17.5 for their resistance all 3 of them. both replacements from rock auto and a sensor from the auto part store. but when i tested the bosch one it came back as 11 ohms of resistance between the heating element. and i did find a service manual but i dont know how reliable it is, it stated the resistance for the heating element is 11-16 ohms of resistance. so i dont know at this point and wish i could just replace the harness entirely. this is why i never mess with electric things and only focus on mechanical stuff lol.

 

Bosch sensors are no bueno in a Lexus. 11-16 ohms is a wide range I don't like seeing that they should all be the same within an ohm or 2 assuming room temperature. Solder is not an issue at all. Need a wiring diagram so you can test right at the power source.

 

oh i know thats why i originally went with denso, i always use oem sensors in cars. and yeah gonna probably need help testing tbh cause i was never good at it lol only mechanical stuff.

 

Heater circuit probably goes right to the ECU. This is an example, not your car just an example!

 

not gonna lie i have no idea how to read wiring diagrams... that is a main issue for me lol.