Aloha!

Got a P0031 code on the Engine and Cruise Control systems. I changed the B1S1 O2 sensor which was verified defective through a multimeter. The new one tested well on the multimeter and seemed to be working until the lights returned a few days later. I checked underneath and saw that I didn’t plug it in good so I plugged it in, and, again, it was good for a few days until the lights returned, I figured it was loose again but it’s plugged in and giving readings on my scan tool.

Any suggestions on my next steps? Currently, the lights are off since I cleared the codes but it’s sure to return for a third time.

Ii don’t think it’s the wiring since the lights only seem to return a few days later. ’m thinking I could test the ECU, but would like some advice on how to test he ECU or something else thst you all can think of. Also, it’s a few days later but it could also be after driving about 5-8 miles rather than the days itself.

thanks in advance!

 

Was it an OEM part you used to replace the sensor ? Or a generic ? New part or used ? The way your fault is reacting makes me think that your ECU is thinking the replacement part meets requirements to begin with but with a longer term testing/sampling cycle over a few more miles, it fails.

 

I used

Denso 234-4167

These were for my downstream sensors.on both sides. Worked out fine after my indy mechanic cleared the codes

 

Yes, I purchased a Denso replacement from Autozone.

 

Hello,

Just to be absolutely clear, are you sure it was the same exact code?

For the sheer thrill of it, you can try to Backprobe the Heater Terminals on the Car's Pigtail (not on the Sensor) and check the Resistance of the Sensor through said Backprobes, the point is to make sure that the Car's Wiring does indeed have Contact with the Sensor. Below is a video on how to do it correctly, just in case. You can then try hooking up a Test Light right to those Backprobes to see if the ECU is even attempting to power the Heater Element at all. Do now use a Multimeter for this test, it doesn't create any Load on the Circuit, there is a good chance it will trick you.


AutoZone should be a good option, even if quite overpriced usually. Here is a good place for Aftermarket parts.

Hope this helps and best of luck!

 

Thanks for the reply.

Yes, P0031 popped up every time. Unfortunately, I don't think I'm able to back probe the pigtail opposite the sensor due to its location (B1S1). Undoing the connectors is hard enough given the lack of space unless I were to remove the steering rack, which I just replaced a few months before the current issue. The timing would've been perfect had the code showed beforehand. I guess I could try to back probe on the sensor side which should respond the same as long as it isn't a wiring issue.

 

Well, that's just about the whole point of this test..

Unfortunately I don't have the Wiring Diagram for those cars, but I do have one for the GS430, which shows that one of the Heater Element Terminals is connected to the B+ Terminal in the OBD1 Diagnostics Connector, and the other to Pin 9 on the ECU, the Pinout of the Connector is shown below. Get a Multimeter and make sure that you do see the Heater Element Resistance between those wires.

Only if you see the Resistance, and preferably verify that it is, in fact, the Sensor's Resistance by Disconnecting it, Backprobe the Pin 9 on the ECU and ensure that the Test Light would turn On when the Engine is Started.



Hope this helps and best of luck!

 

Thanks, I'll give that a try. I appreciate your help.

 

I appreciate all the help. I was able to finally find a way to retrieve the connector harness behind the engine with enough room to see that one wire was pulled through separating the connection at the connector. With the mystery solved, any ideas on the best way to approach this? I'm thinking I'll just buy a new pigtail directly from Lexus and use Posi-lock connectors.

 

Here is a thread on Wiring Repair, it contains Part Numbers for just about any Connector and Terminal used by Toyota, and the process on De-Pinning the Connector. That thread also describes the process and the tools required for a Splice Joint, as well as the process of replacing just the Terminals if your Wire broke right at the Seal of the Connector, making the repair virtually undetectable if done right. Seeing the cost of those crimps, make sure to get plenty of spares such that you would have something to train on before attacking your actual Harness.

While at it, check if any other wire is damaged in any way, a lot of times you will see the Insulation getting torn right at the root of the Seal in those connectors, just like it's shown in the thread linked earlier. If that's the case, I would strongly suggest to get extra Terminals and Seals, and Re-Crimp all 4 Terminals, such that the Insulation is intact again.

You can, but it does tend to be expensive. The thread linked earlier also contains links to places that have the same exact connectors, made by the same companies as the OEM, just considerably cheaper than the Dealership will charge you.

Don't even think about it, those are just one step above simply twisting the wires together. I usually don't like being too critical of something, but in this case, those Posi-Lock Connectors are a complete junk in general, and especially so for the High Power Wiring on the Exterior of a Car. Crimp Terminals described in the thread above are just about free in comparison and are just as easy to use if you get the hang of it, but the resulting joint will keep being durable for years to come.

Hope this helps and best of luck!

 

Thanks for being such a big help!

 

I also remember that in the past, some of the units used to check the cars diagnostic system, also triggered a check engine light. I had a mechanic awhile back & his unit would always set my code off. This may not be your issue, but just something else to consider

 

Yes, my scanner does set off my system when I use it with the vehicle running. A simple zero point calibration and code reset fixes the issue. Thanks!

 

My issue has been fixed!

For anyone else looking to replace the B1S1 oxygen / O2 sensor, if I were to do it again, I'd remove the sensor from the car, and pull it out from behind the engine, following the path of the O2 wiring. This means you have to leave the connectors connected, and dismount the O2 connectors from the body clip. After you pull it out from behind the engine, you can then separate the connectors to remove the old O2 sensor, connect the new O2 sensor wiring and reroute the sensor the same way you removed it. To remember the correct routing, which isn't difficult even if you don't take this step, I sent a plastic wire worm tool from underneath the car and behind the engine. I hope this helps!