LA4Mead

I'm getting four codes from a new scanner I bought just for this purpose, and wondering if anyone can help me with advice to find the faulty sensor(s) to diagnose, clean or replace. Two of the codes are followed by a "P", and the scanner's documentation isn't clear. I think they are trying to say the code is "pending" but I don't know what they mean by that (either it is getting an error or it isn't?).
P0125
P1155
P1150 P (pending?)
P1155 P (pending?) (repeated as the fourth code)

Using a chart I'm very thankful I found in another thread on this forum, I found these descriptions:
P0125 closed loop fuel ctrl insufficient coolant temp
P1155 a/f ratio sensor htr circuit malf bank 1 sensor 1
P1150 P (pending? huh?) a/f ratio sensor circuit/performance malf. bank 2 sensor 1

My car is a '99 RX300 (5/98) 2WD, mileage is +/- 130,000miles now. After some maintenence around 120,000 miles (timing belts, plugs, etc) got CEL and was told by a Toyota dealer "needs a new MAFS", I removed the original MAFS and carefully sprayed it with CRC MAFS cleaner and the other loop on the MAFS (is that an air temp. sensor?). I replaced the cleaned (original sensor) and had no CEL error for many months. Could these codes be from the same problem (completely different symptoms) and it's time to replace MAFS and that's all it needs? Hey, if that's whats wrong, the car deserves a new one.

Any ideas/advice which sensors I need to check or what might be wrong? The car runs fine, but I get a CEL trigger (The CEL stays on at restart, an error lights the "Trak Off" lamp) consistently after the engine temp guage indicates full normal operating temperature. The Trak Off light does not stay on after restart until full operating temp and something triggers the error, but the CEL stays on. Gosh those lights are annoying on a dark road. And it would be nice to have the "trac" stay on all the time in case of more rain.

Thanks!

carguy07

My money says Bank 2 Sensor 1. Ignore the P0125. P1150 & P1155 are both Bank 2 Sensor 1. This is the air fuel sensor in the front by the radiator.

https://www.clublexus.com/forums/rx-...el-sensor.html

http://www.amazon.com/gp/product/B000C5YCZ2

bearbrew

I'm with carguy07 on this one. With the mileage you have you can consider yourself lucky. The sensors on my 2000 RX300 gave up around 68,000 miles. I am sure some of that has to do with the fact it's the wife's ride and it does see quite a lot of short drives to the store and back. Not getting to full operating temperature may have something to do with the sensors going bad.
The best source for the sensors has been Amazon.com with a price around $125.00 shipped and sometimes less.
The Denso brand is the one you want which is a direct replacement and the P/N is 234-9009. The other aftermarket ones seem to create problems as they may have different electrical values.
The hardest part of changing the sensors seems to be unplugging the electrical connector. Keep after it and it will come apart.

LA4Mead

Thanks both for the info. I just want to verify a couple things. If I understand you correctly:

1. Should I disregard code #1, P0125 (Closed loop fuel ctrl insufficient coolant temp) ?

2. Code 2: P1155 (A/F ratio sensor htr circuit malf bank 1 sensor 1) Is it correct that I assume it's not really bank 1 like the lookup says, but really bank 2? Is bank 2 the front sensor in the manifold right up front (the easiest to access) behind the radiator?

3. Codes 3 & 4 (p for pending? what's up with that?) Those are for bank 1 and bank 2. I should also ignore these?

4. Are the codes for bank 1 and (pending?) for bank 2 A/F ratio sensor what I would recognize on other cars (Ford) as manifold 02 oxygen sensors, but their correct name is A/F ratio sensor?

5. (sorry so many questions) I don't have $ to throw away right now, but if it's time, should I just order both (?bank 1 and bank 2?) front and rear manifold A/F sensors? And are they both the same part # or different like on Fords?

I really appreciate the input. Thanks folks.

carguy07

1) Yep, disregard.

2) P1150 & P1155 are both codes for bank 2 sensor 1, the air fuel sensor in the exhaust manifold by the radiator.

3) The pending codes are readable before the check engine light comes on. More of a warning of an impending problem. No big deal, they are pointing to the same sensor.

4) Yes, would be called an oxygen sensor on most cars, more of a play on words. Think really good oxygen sensor and now it's an air fuel sensor.

5) Same part for both banks. While under warranty, my dealer replaced both of them at the same time even though it was only showing a code for one. I just had one fail on my car recently a second time (not under warranty anymore) and since it is $100 part, I just replaced the bad one and the car seems to be just fine. If the other one acts up I can always pop a new one in there too.


There seems to be some confusion when looking up the codes. Not sure if they can mean different things on different makes. But the factory manual says both of those codes are bank 2 sensor 1.

LA4Mead

Great!

First I'm going to CRC spray clean into the intake manifolds and clean out the system (don't want to do that with new sensor(s)), clear the codes, and order & replace the front A/F sensor.

Then I'll post what happens. Hopefully all will be AOK.

P.S. I think I can use the same 7/8" oxygen sensor socket (slotted for the sensor lead) that I use for the Fords. It seems to be the right size even tho it's not metric. I'll first try breaking it free with a metric open end wrench (is it 22mm?)

Does this sound like what others have done? Is it 22mm?

Thanks for your help. Sounds like this is going to be pretty easy.

noku

Actually P1155 is bank 1 sensor 1, yeah the one up against your fire wall (pita). You could try replacing bank 2 sensor first and see if all the codes clear. The P0125 is ECT engine coolant temperature sensor near engine end of top radiator hose. If this needs changing try NAPA"s, they charged me about $20 for a V-6 Camry ECT sensor (believe that they're exactly alike), Carquest wanted about $50 and O'Reilly's (Checkers) wanted over $130, no Autozone here. Wrap the threads w/ teflon tape but don't tie it down too much because much of it is made of copper and could snap. In this case less is better, only coolant would seep out if too loose. Check at normal operating temp.

It's 7/8" on the a/f sensors, I think almost exactly like 22mm (both would work).

noku

Forgot to add that sometimes the guys at the parts store think the ECT sensor is the one which controls your electric fans and located at the bottom of the radiator. Tell them it's NOT that one.

LA4Mead

I ‘m guessing it's the a/f sensor facing the firewall; I ordered one to replace that one first and see if it still gives a code for the (easy) one that faces the radiator toward the front. The codes I'm getting show that rear bank sensor has a heat circuit failure (bank 1 sensor 1).

The code for the bank 2 (front) sensor says perf malf... could it be it shows that code when comparing the two? I may still have to replace that one - is it a good idea to change both anyway (so they will provide a similar reading due to their "newness")?

I'm still open to suggestions. Thanks everyone... I'll post what I find out.

hypervish

If it were me, I'd just replace both, because eventually it's going to die, and the mpg gain will be a nice bonus.

But, then again why fix something that isn't broken.

noku

At over 130K, your sensors going to die sooner rather than later if still original. If you got the funds why not? You must have access to good gas as these sensors longevity seems to be extended by using premium fuel.

Also be aware that if the codes do not clear, it may be because of an exhaust leak somewhere in your system. Probably near the engine area (exhaust manifold, flex joint, associated gaskets or pipe). Read about this someplace but not sure where.

hypervish

I agree using higher octane has led to extended life of oxygen sensors, well at least in my case. I got 156k out of my sensor, using solely 93 octane till about 110k, and then I started used 91 occasionally.

LA4Mead

Well I'm not sure extra octane helps extend the life of the A/F sensors or not. More likely it's the formulation of the fuel. In So Cal, this varies from region to region and may include ethanol differences. I usually only use Chevron 87 or ARCO 87. I do clean the fuel injectors by dousing with the intake with CRC while running the engine part throttle (it's tricky to keep the engine running while you're doing this and bypassing the intake). I do that at least once per year. I also use Techron or other good quality alcohol-free cleaner in the fuel a few times per year, and I've been known to drive with a lead foot (not much dirty carbon accumulating in there). But I'm tip-toeing much more often now to maximize mpg which on the RX300 makes a big difference. I'm satisfied with how long the sensors lasted and the ease of replacing them DIY compared to the cost and hassle of a L or T dealer visit.

Now that it's done here's how it came out with the p0125, p1150, p1155 codes:

I first replaced bank 1 sensor 1, the a/f sensor in the rear manifold by the firewall, because it was throwing a code that included that sensor's heater (and it was a little more awkward, but not bad). With the new sensor installed, I cleared the memory using the scan tool. After the drive cycle, the CEL & TRAC Off came on again, and the scanner showed the same codes with a p0171 as well. So then I replaced the front sensor (a five minute chore). The codes have stayed clear even after a 330 mile trip. I bought the Denso 234-9009 sensors from Amazon, I think they were $105 each with free ground shipping (I got them pretty fast).

Before trying to remove the a/f sensors I carefully sprayed liquid wrench on the threads of the old sensor, carefully tapped with hammar on the handle of a screwdriver, point touching the threads, and went on to figure out the connector. Disconnecting was made extremely easy by photos on another thread on this forum. It was a cinch. I took more time to jack the car up on a stand (to replace the rear sensor accessed from underneath) than the actual work did.

I believe I averaged over 24 mpg on this recent trip, despite high winds and mountain roads. This is better mileage than I've been getting lately, and is about what I was getting when the car was new 13 years ago.

Thanks for the help from all who contributed. Car repairs on 13 year old cars should always be so easy.

carguy07

So since the factory manual says that those codes are for the front sensor and it sounds like it was the front sensor that fixed it, is there a pretty decent chance that the manual is correct? Not trying to be a smart a$$, because I honestly don't know the answer. That is what I was trying to get at earlier.

LA4Mead

Yes, it's very likely the look-up information is incorrect, and that yours was correct. I decided to tackle the one underneath the car first since I had information both ways. I'm glad you had a shop manual; I looked up the codes from various sources and they all said p1155 was the bank 1 sensor (heater circuit) failure, when your information said it was bank 2 (front). The information you found is likely the right one since the error codes came back when I replaced the bank 1 sensor but went away after replacing both. I'm not motivated to put the old one back in bank 1 to see if it's OK because it's already lead a long life. I did wonder that it was highly unlikely both went bad at the same time, unless it was bad fuel, but the car ran fine the whole time.

The only other explaination I can conclude is that the new bank 1 sensor in combination with an old sensor in bank 2 had resistance values so different, they needed to be replaced at the same time.

Thanks again for your help Carguy and everyone . All the posts were helpful.