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98 Corollah LE
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Discussion Starter · #1 ·
I keep getting a P0125 trouble code in my 98 LE... The car is driving fine but the √EL keeps coming on after I clear it . Yesterday I got P0125, P0130 & P0133, but today it's just the 125. The bank 1 02 sensor is about 4 mos old, and is a cheapy. I hate friggen working on cars in the cold. Anyone have anything better to say than it's prolly the 02 sensor b4 I go and freeze my balls off? Saying it could be the computer is not allowed. :crying:
 

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05 camry 07 tacoma
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Well, besides sensor itself, consider the wiring/connector.
Existing sensor came with attached pigtail connector or is it a cut/splice?
Rockauto.com has the correct Denso sensor for around $50.00.

Can you read engine parameters- fuel trims etc? Engine starts/idles/runs ok?
 

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98 Corollah LE
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Discussion Starter · #3 ·
That's actually real good advice. I practically live on Rock Auto and never even thought to look for the 02 sensor there b/c I figured it would be $200.

The weird thing is the P0125 trouble code. Why does it say "insufficient coolant temp for closed loop fuel control". What does coolant temp have to do with this and could it be something besides the 02 sensor? Why doesn't it dispell the big mystery and just say what part is failing?
 

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05 camry 07 tacoma
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Ref meaning of P0125, check the www.obd-codes.com site discussions.
Toyota in particular uses this code to refer to the delay in time for the O2 sensor to come up to operating temp.
Could be the heater in the universal O2 sensor isn't up to OEM spec for the cold weather.
 

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98 Corollah LE
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Discussion Starter · #6 ·
Well, I'd believe that of a $20 replacement 02 sensor and Toyota. I will check the coolant level and nose around the engine today. I have not replaced the coolant or t-stat in years. In fact, I don't even know where the t-stat housing is. Is it burried on top somewhere? The top radiator hose simply vanishes as it goes over the engine, burried by wires and other such stuff.
 

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98 Corollah LE
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Discussion Starter · #8 ·
Oh man, the alternator has to come out to replace the t-stat... damn! I replaced the alternator last summer. Shoulda replaced the t-stat and ECT then. Who knew.

I will definitely keep this thread posted on what fixes it and what doesn't. Hopefully it will benefit someone with the same issue.
 

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1997 Corolla
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The weird thing is the P0125 trouble code. Why does it say "insufficient coolant temp for closed loop fuel control". What does coolant temp have to do with this and could it be something besides the 02 sensor? Why doesn't it dispell the big mystery and just say what part is failing?
It doesn't have anything to do with the coolant temperature really. Read your repair manual section on P0125. It explains that this code is related to the heating element built into the O2 sensor. The heating element gets the O2 sensor up to operating temperature faster so the computer can start using the feedback from the O2 sensor sooner.

Use your scan tool the read the coolant temperature while the engine is running. Does it go to 180F and stay around there? Then you don't have a problem with your thermostat.
 
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98 Corollah LE
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Discussion Starter · #10 ·
Yeah, I get it now. It just baffles me why they would lead you towards a coolant issue when the code just as easily coulda said the 02 heater wasn't working. I'm sure there's a logic to it.

So, should I assume the up stream 02 sensor is working, just not heating up fast enough, b/c I'm not getting any other codes, right?

If so, I'm putting a f'n piece of electrical tape over the √E light on the cluster until spring!:grin:
 

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I checked coolant temperature sensor with multimeter. And reading is fine according to data sheet. Eventhough i replaced it with a new sensor. During test drive, after reaching above 80°C temperature, it shows "Open loop due to system failure" in Fuel system Status and check engine, VSC and TRAC OFF lights on. And P0125 codes appears.
=> Coolant system is working fine, which means thermostat is also working fine

Interesting thing:
After getting the system failure, I stopped the car and turn off the engine. And i started the engine and did a test drive.
Now the system is on "closed loop, usingoxygen sensor feedback to determine fuel mix". Which means now everything is working fine.

Conclusion:
The failure error P0125 comes when i start driving with cold engine, stays in open loop system.
Already warmed engine works fine without error, means goes to closed loop system.

Anybody has any idea what could be the reason behind this.
Please help...
Thank you in Advance
 

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05 camry 07 tacoma
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Likely the code is being set because O2 sensor is not active enough from a cold start up.
Possibly sensor or sensor heater circuit at fault.
Reason behind this is for emissions standard compliance.
 

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Is it something wrong with my S1B1 sensor?
I checked the resistance of the heater coil in O2 sensor. It has some 6.7 ohm value when its cold (22°C). And it has more value when engine is on.
Rectangle Font Slope Parallel Pattern
 

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マズダスピード3
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Is it something wrong with my S1B1 sensor?
I checked the resistance of the heater coil in O2 sensor. It has some 6.7 ohm value when its cold (22°C). And it has more value when engine is on. View attachment 325436
Best way to test is to remove the sensor and apply heat while measuring with multimeter. It should reach 600F and fall quickly. If it falls slow, it's failing.
 

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2000 Corolla CE, 186k miles, AT
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Dr Z and others answered this and helped me on the same thing. It's probably the same O2 sensor issue, not allowing it to go into closed loop. First rule of fight club, don't buy cheaper parts. Otherwise, you'll just do the job twice.
 
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