wtdt

Switched to regular octane gasoline about a year ago, about 6 months later one sensor failed now a second (both in front of the cat). Car is a 1999 LX470 with only 70,000 miles on it-- is the gasoline the cause, manual says regular can be used, gas cap says premium only -- is the low octane the culprit or just the age even though the miles are so low? Thanks for the help.

2003lx470

It can't be the gas....... ? age. I use regular on lx470.

wtdt

Age? What are you asking, sorry I don't follow?

2003lx470

? age= probably age of the truck. I don't think it has any thing thing to do with your gas switch.

osomoso

Doubt it would be the difference in octane levels. Sounds about the right time for new
o2 sensors. Did mine at around 80k.

osomoso

Funny thing, I've been a member here for five years and just hit 200 posts. Sorry, off topic;-)

Gregz_IS

Odds of two parts failing in the exact same way at the same time is pretty much the same odds as winning the powerball lottery.

You didnt list whether the codes were related to system lean or rich... or if the codes were related to O2 sensor heater circuit failures.

I'm betting that the O2 sensors are just fine. They are reporting a mixture related problem.

If the codes are both either lean or rich codes it is something that effects total fuel mixture (whole engine) ... vacuum leaks, MAF, fuel pressure ..etc.

Way too many possibilities... but throwing new sensors on this vehicle without diagnosing the actual problem will just be wasting $$$.

Get the vehicle diagnosed properly... spend some $$ on a proper diagnosis then you wont be throwing $$$ down a hole.


just my advise.






oh ......and I'm not just another internet wannabe mechanic

ASE Master Technician since 1982
ASE L-1 certified since 1994
Automotive Instructor 20+ years

2003lx470

Way too many possibilities... but throwing new sensors on this vehicle without diagnosing the actual problem will just be wasting $$$.

Get the vehicle diagnosed properly... spend some $$ on a proper diagnosis then you wont be throwing $$$ down a hole.

--------------------------
This is VERY TRUE.

Last month I had to replace O2 Sensors on my toyota. I took the car to my trusted mechanic. He said my bank-2 O2 sensor was bad.....replaced it with a new one. Engine light kept coming back. Then I had to replace the bank-1 O2 sensor. O2 sensors are expensive. Make sure you find the bad sensor and replace only that one.

wtdt

The P135 and P155 codes both read identical, like this...
heater system malfunction
probable cause:
open or short circuit condition
poor electrical connection
faulty a/f sensor
faulty HO2511
Sorry, probably stated it wrong before but sensors failed about 6 months apart, not at the same time, P135 first then P155 with both in front of the cat -- hope you can give me more advice having this info.

And thanks everyone sounds like good advice -- however, when I first searched this site found many entries for other lexus models where people were saying they had switched to regular and were having mutiple 02 sensor failures and the comments that came back seemed to be in agreement that the sensors were "too sensitive" and were damaged by the regular gas??? Didn't look at the credentials of the people who came to that conclusion so maybe it was just conjecture on their part?

Gregz_IS

Both codes are heater circuit malfunction codes.

Inside the O2 sensor is a ceramic heating element that heats the sensor to approx. 800 degrees F. within a few seconds. This helps the computer to be able to put the system into closed loop fuel control quickly after startup. It maintains the temperature of the sensing element during prolonged idle so fuel control can be kept within proper limits.

Without the sensors operating properly the system takes longer to achieve closed loop and can fall out of fuel control during proloned idle.

Diagnosing heater circuit problems usually requires verifying proper voltage and ground on the heater circuit then measuring the heaters internal resistance. If the heater in the sensor is found to be faulty then replacement is necessary.

After replacement proper operation of fuel control should be verified by monitoring fuel trims and verifying the heaters pass the OBD II O2 sensor heater circuit monitor and readiness status trips to "ready" with no current or pending heater circuit codes.

Be aware that when certain codes are present in the computer there are other system tests that cannot be run. After the fault is repaired and the system is able to run the test routines that were previously blocked there may be other faults that now come to light.

When a system fault involving fuel control (O2 sensor faults) occurs it may cause damage to the catalytic converter if allowed to operate with the fault for a prolonged period of time since proper fuel control may not be possible with the fault occuring.

This is one reason to get system faults repaired when they occur instead of hoping they will just go away.


On a side note.... the octane of the fuel has no effect on the O2 sensor. It is just another myth passed around on the net. Just file it with the other internet myths about gasoline.... like 93 octane burns hotter than 87 octane (myth) and using aviation fuel gives way more power (old myth).

With some dedicated research most of these myths are easily debunked. But gaining true knowlege takes work and understanding of the science of thermodynamics and combustion but good information is hard to find among the trash spread on the net.


Hope this helps. Good luck.

wtdt

Thank you so much... just hope I haven't waited too long and damaged the cat -- will take your info to my mechanic and hope he can do what needs to be done -- can't afford Lexus service these days.

wtdt

Took the LX470 to an auto electric specialty shop today, their first opinion was that it was too early for two sensors to fail, so they tested it on a mentor unit, came up with the same codes, then they ran all the diagnostic tests and the specs all came up perfect showing that all the ratio's were right where they should be and that the sensors were operating perfectly and nothing was wrong with the sensors -- suggested I should take the car for a long drive on the highway 45 minutes or more and see if the check engine light comes back on after they reset it (no charge for about 30 mintues of work by the way). Did that, then parked the car, came back out an hour later drove a couple hundred feet and the check engine light came back on -- they said to come back and they would pull the two O2 sensors and check them if that happened and test them out of the car -- their opinion was if the check engine light did come back on it was probably just the age of the car and they might have to be changed after all -- these guys are obviously honest, but just wondering if you have any other suggestions that might guide them? Thanks again.