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Help On Trouble Codes For 2000 Rx300


tomb57
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I need some guidance on what to do next. I had a PO125 code (insufficent coolant temp for closed loop system) and I replaced the thermostat. No more PO125. I reset the code and now after only 2 miles, I have a P1130, P1150 and shortly thereafter a PO171. Do I replace the AF (02?) sensor next or replace the MAF sensor (I've tried cleaning it) I should mention that the gas mileage is way down, and the truck seems to be surging. Thanks for any help, you can give me before I have to pay the big bucks to get it fixed.

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I don't have the exact answer to your question, but I must say, when I get a CEL, I ALWAYS cancel it out and run the car and see what comes up when the CEL comes on again (if it does!) If you have a scanner or device to cancel the CEL, do it a 2nd or even a 3rd time and record what the codes were each time. IF you chase codes, you're often gonna be replacing a lot of parts that didn't need replacing. It has an electronic brain, not a human brain and many times will send you on a wild goose chase. Do what I suggested and if you don't own a scanner, you should buy one, it will pay for itself. A good possibility you didn't need the thermostat. By the way, though a lot of people call 'em Oxygen sensors, they're not, they're A/F ratio sensors. The only O2 sensor is behind the CC under the drivers seat.

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I don't have the exact answer to your question, but I must say, when I get a CEL, I ALWAYS cancel it out and run the car and see what comes up when the CEL comes on again (if it does!) If you have a scanner or device to cancel the CEL, do it a 2nd or even a 3rd time and record what the codes were each time. IF you chase codes, you're often gonna be replacing a lot of parts that didn't need replacing. It has an electronic brain, not a human brain and many times will send you on a wild goose chase. Do what I suggested and if you don't own a scanner, you should buy one, it will pay for itself. A good possibility you didn't need the thermostat. By the way, though a lot of people call 'em Oxygen sensors, they're not, they're A/F ratio sensors. The only O2 sensor is behind the CC under the drivers seat.

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Thanks for for the info on the A/F sensor. I did clear codes and when the CEL came on I pulled over and checked the code. This only took about 2 miles, then after another mile or so, the PO171 came up. Also I was watching the O2 values (don't know what to expect) but very little voltage movement. By the way I was using an OBD2 scanner. Would getting a new MAF be worth it for $54.? Could that clear the 1130 and 1150 codes?

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Don't know what you mean when you say "very little voltage movement". Does your scanner "read" the running A/F ratio sensor operation? Unlike O2 sensors, A/F ratio sensors constantly "swing" to a much wider range of voltage in the normal course of operation. It may take a little digging, but this site has a ton of good information as well as good answers to your questions. Get to know the site and it will provide answers to a lot of the questions you may have without "throwing" parts at the problem. http://www.obd-codes.com/trouble_codes/lexus/

You have to "wander" the site because it has a lot of "tenacles" to it.

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Don't know what you mean when you say "very little voltage movement". Does your scanner "read" the running A/F ratio sensor operation? Unlike O2 sensors, A/F ratio sensors constantly "swing" to a much wider range of voltage in the normal course of operation. It may take a little digging, but this site has a ton of good information as well as good answers to your questions. Get to know the site and it will provide answers to a lot of the questions you may have without "throwing" parts at the problem. http://www.obd-codes.com/trouble_codes/lexus/

You have to "wander" the site because it has a lot of "tenacles" to it.

Having run the engine over a long period of time outside of closed loop mode may have caused a modification of the O2 sensors's metallic make-up. It may take 200-300 miles of closed loop driving to clear the sensors.

My basis for that statement:

Just after I purchased, new, our '01 AWD RX300, I had an incident that required semi-continuous engagement of TC (MUDDY dirt road), lots of front braking apllication and virtually FULL engine dethrottling. A short time later I got a CEL (& VSC) which would not remain cleared via resetting so I purchased a new O2 sensor. Before I took the time to install the new sensor the CEL cleared of itsself.

A few months ago I had a repeat of the same situation and ended up, again, with a CEL (& VSC).

My '01 is NOT DBW so the engine dethrottling is accomplished via EFI fuel starvation. That results, of course, in a very oxygen RICH exhaust flow. Apparently the RICH oxygen flow has some adverse effect on the sensing element of the O2 sensors.

So, just as before, after a driving 2-300 miles, the CEL cleared on/of its very own.

Anyone interested in buying a 10 year old, NEW, never used, O2 sensor..?

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I'm still having problems and bad gas mileage. Here's the latest glue. If I reset the CEL and drive the truck for one continous trip 20-30 miles or whatever, and it gets good mileage, no CEL comes on. If you stop and turn it off and then a while later start and go, the CEL comes on after a couple miles, and the MPG starts goung down. What's happening? Also, yes I may be interested in the Oxygen sens or for sale.

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