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Cel Codes P0125, P1150, And P1155


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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?).



P1150 P (pending?)

P1155 P (pending?) (repeated same as #2, but as the fourth code with a P after it.)

Using a chart I'm very thankful I found in another forum, I found these general 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 an early '99 RX300 (5/98) 2WD, mileage is +/- 130,000miles now. After some maintenance around 120,000 miles (timing belts, plugs, etc) got CEL and was told by a Toyota dealer "needs a new MAFS". I read other owners had cleaned it and reused it (and had done this before). So I removed my 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.


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  • 7 months later...

P0125 Insufficient Coolant Temp. for Closed Loop Fuel Control. I've read a lot of forums about people saying this is a coolant temp sensor or thermostat, but TIS (Toyota Information System) says that is has to do with an A/F (air/fuel ratio) sensor. Here is the condition and trouble area directly from TIS. (I've worked for Toyota and Lexus for a few years and have access to to TIS);

DTC Detecting Condition; P0125 After the engine is warmed up, A/F sensor output* does not change when conditions (a), (B), and © continue for at least 1.5 min.

*: The output value changes at the inside of the ECM only.

(a) Engine speed: 1,500 rpm or more

(B) Vehicle speed: 40 ∼ 100 km/h (25 ∼ 62 mph)

© Throttle valve does not fully close

Trouble Area;

Open or short in A/F sensor circuit (bank 1, 2 sensor 1)

A/F sensor (bank 1, 2 sensor 1)


DTC P1155 A/F Sensor Heater Circuit Malfunction (Bank 2 Sensor 1) (the front of the motor, upstream sensor)

If you open the hood and look straight down at the exhaust manifold, that's the sensor that's faulty.

DTC Detecting Condition;

Heater current of 0.25 A or less when the heater operates (2 trip detection logic)

Trouble Area;

Open or in heater circuit of A/F sensor

(bank 1, 2 sensor 1)

A/F sensor (bank 1, 2 sensor 1) heater


DTC P1150 A/F Sensor Circuit Range/Performance

Malfunction (Bank 2 Sensor 1)


Refer to DTC P0125 (Insufficient Coolant Temp. for Closed Loop Fuel Control)

Open or short in A/F sensor (bank 1, 2 sensor 1) circuit

A/F sensor (bank 1, 2 sensor 1)


You may as well replace both A/F sensors because if the one on the front of the car is faulty then the other one towards the rear of the car is probably right behind it. We replaced our b2s1 a/f sensor, then the motor went t*ts up and I had to replace/rebuild another motor. The vehicle was down for quite a few months while I did this. I just got it running a couple months ago now we have a P0125 and P01135 codes, now we have to replace the rearward a/f sensor (which is bank 1 sensor 1). The sensor on the front of the car, top of the motor is bank 2 sensor 1

Hope this helps.

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  • 2 years later...

He is trying to tell you that you probably have a bad Air/fuel sensor....pursue that first, than reset the codes and see what happens. The car is not junk, just having a problem...though when it has problems we all feel like it is junk....Follow the code for the first bad sensor,(air/fuel). There is a heater going both sensors which is wire in series, so if one is bad both will register a bad heater voltage unless you check them individually.

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Code - P0171, P0125, P0330, P1150, P1155. I am certain one problem triggers multiple codes. I have cleaned the MAF with CRC maf cleaner. New air filter, thoroughly disassembled and cleaned intake throttle body, IACV, throttle position sensor, checked all hoses for damage, cleaned with electrical cleaner all connectors, cleaned and swapped the speed sensors in transmission.. I will run ohm check on the air fuel ratio sensors.

Can a faulty PCV cause these codes?

Car has 254,000 miles. All maintenance performed per mfg. recommendations. Love the car just tired of chasing codes.

Transmission periodically not shifting into overdrive is what started this challenge.

This forum is the best in the industry as I have two other makes of vehicles. Their forums are lacking.

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