ChrisMau

Hey everyone - I'm new here but having some CEL with my 1999 RX300 and thought the friendly people here could help.

First
Ran the codes
P0125
P1133
P1135

Then
Watched the the scan tool on a test drive.
It looks like it doesn't want to get out of open loop mode.
But after watching the engine temp rise on the scan tool from 70 deg to 180 deg and stabilize at 180 within 5-6 minutes it doesn't seem to be a problem with engine temp. Intake air stays accurate at about 70-80 degrees. Coolant is full and I just had the thermostat replaced a couple months ago.
p0125 is insufficient coolant warm up so maybe that's a false code???

following
I tested the Bank 2 sensor 1, A/F sensor (cuz it's so easy to get to and my kids are always needing something) The resistance not even registering. I went and got a new denso from NAPA for way too much money ($180). I brought my multimeter and tested it to be cautious. Resistance was in-spec at 1.2ohm.

and then
Reinstalled sensor at Bank 2 sensor 1. Cleared codes and test drove. Now I got the P125 again and the realtime Fuel system monitor says "Open loop mode due to acceleration or braking" or something like that. Dang

Next
I gotta check Bank 1 Sensor 1 and the I suppose the ECT.
Why would the ECT be giving me a P0125 when I can watch the temp rise as expected from the scan tool?
If Bank 2 sensor 1 what are the chances Bank 1 sensor 1 went bad?

I guess I'll test the other upstream sensor and maybe I'll clean the MAS just for grins.

Car doesn't run much worse but there is definitely some smelly exhaust.

carguy07

I think you just need to put the new sensor in Bank 1 and it will be fine. Ignore P0125, it's a false code.

artbuc

As posted, in this case p0125 is a companion code so you can ignore it. Why did you change Bank 2 when your codes are for Bank 1? You say you checked Bank 2 sensor resistance. Which circuit did you check, the heater circuit or the sensor circuit?

roseyyz

Hi, I've read few posts about this "disregard" p0125 code or ignore it etc... I recently changed MAF and knock sensors and so far is running fine (no knocking/pinging and finally overdrive )
I disconnected battery for a while etc and now only code is that infamous P0125!! so my question is.. what is it? I don't want to ignore it.. I just don't like having the check engine light 24/7 I would appreciate ANY information about this. Can it be the Engine Coolant temperature sensor?

salimshah

When you have multiple codes, the strategy is to focus on some and ignore some. Once all other codes are addressed then the final or remaining code needs to be investigated.

If all other codes are gone then P0125 must be repaired. So what does the temp gauge read? It can be the temp sensor or it can be the connector left off.

Salim

artbuc

Do a Google search. In 5 seconds you can read all you need to know about P0125. Any problem that prevents closed loop operation could throw P0125. It you get only P0125, you may have an issue with your ECT (easily checked with a VOM), thermostat or low coolant.

http://www.obd-codes.com/p0125

roseyyz

Thanks a lot for your help, I really appreciate it

ChrisMau

Thanks for the responses. I'm happy to report my problem is fixed by replacing both the O2 sensor located in the exhaust manifold (AT sensors)

I'm really glad I was able to fix this myself and easily saved $500 over dealer parts and labor.

Below are some key notes

The AT sensor MUST be DENSO don't mess around with other brands.
BUY It from Amazon and they go for ~$90 each. NAPA sells the part for $180, probably same price as a dealer.

22mm Wrench or offset sensor wrench is helpful for Bank 1 Sensor 1. I got a powerbuilt from Amazon for $10 when I ordered the sensors. Crescent wrench can be used for Bank 2 sensor 1.

Bank 2 Sensor 1 is easy breezy, it's right in the front and you need only a crescent wrench or 22mm wrench.

Bank 1 sensor 1 is kind of a pain to reach.
For the pigtail clip go up under the hood stand on a high step stool and reach through to the clip in in between the top engine parts. There is only room for a average sized forearm. I had to really jam my arm in. Then I reached around the engine parts with my left arm and was able to grab the cable and pull it loose while squeezing the clip. You might have better luck with an assistant underneath. In order to get the sensor unscrewed I raised the front of the vehicle and crept under and removed it the sensor. I didn't need any penetrating spray. Just uses some muscle.
To install I clipped the pigtail into it's harness from the top of the engine and then slowly lowered the sensor end down before creeping under to screw in. Don't lower your sensor before you clip it as you could drop it before it's clipped. You don't want to drop sensors.

Before you start threading the sensor put some anti-sieze on it. The DENSO brand comes with a tube, so no need to buy extra. Finally twist the sensor counterclockwise to offset the clock-wise twisting while your screw in as it's probably better not to twist up the pigtail when installing.

Finally I cleared the code with the "torque" OBD app and Bluetooth scanner tool. Also helpful in diagnosis was configuring a graph display for the O2 sensors. I could see no change in the readings when it was bad. I also could see the engine openloop closed loop engine status. I could see that after install and warm-up the O2 sensor was reading variance.

In both cases I tested the old sensors with an ohm meter and they registered Infinite resistance. The new sensors measure 0.8Ohm.I recommend testing the old sensor before opening/installing the new one. You can not return opened electronic parts. If it the part test okay it may be something another problem. Also it's smart to test the new sensors during installation just for sanities sake.

Good luck. I hope my notes help.