1997 Lexus LX450 P0125 Code

LEXUS
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RMUNSCH
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I'm working on a '97 Lexus LX450. I just replaced the engine after it failed the head gasket. Now it's showing a diagnostic code of "P0125...closed loop fuel system...insufficient coolant temp." I have replaced the thermostat & cancelled the code but after about two or three miles, the check engine light comes back on. Thanks, Ray
Jan 7, 2007 at 6:48 AM
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SERVICE WRITER
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Indicates the ECT or CHT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting the engine.

possible causes:
Insufficient warm up time
Low engine coolant level
Leaking or stuck open thermostat
Malfunctioning ECT sensor
Malfunctioning CHT sensor
Jan 7, 2007 at 11:31 AM
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SERVICE WRITER
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Ray,
Getting infomation is such a PITA, and conflicting too. At work I checked alldata and according to that it points to your front oxygen sensor. I'm more inclined to go by this than my previous post.

I'm a service writer . what can I tell you?
Jan 8, 2007 at 10:14 AM
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CARUNDELL
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[quote:27fa637540="rmunsch"]I'm working on a '97 Lexus LX450. I just replaced the engine after it failed the head gasket. Now it's showing a diagnostic code of "P0125...closed loop fuel system...insufficient coolant temp." I have replaced the thermostat & cancelled the code but after about two or three miles, the check engine light comes back on. Thanks, Ray[/quote:27fa637540]

Hey, Yeah one of toyota/lexus shining moments......code desciption points you in the wrong direction ....... O2 is the cause, and was damaged by coolant when the head gasket failed.

Chris
Jan 14, 2007 at 9:14 PM
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Suggested Repair

Test and likely replace the front oxygen sensor, which may have been damaged by coolant when the head gasket failed. Also confirm coolant level and that the new thermostat is closing and allowing the engine to warm up.

Conversation Summary

After an engine replacement for a failed head gasket, a 1997 Lexus LX450 sets P0125 (insufficient coolant temperature for closed loop) within a few miles even after a thermostat replacement and code clear. Initial guidance listed warm-up time, coolant level, thermostat, and coolant-temperature sensors. Later replies said the code description can be misleading on this Toyota/Lexus and pointed to a front oxygen sensor damaged by coolant from the head-gasket failure.

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