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Does my Toyota dealership know what they are doing? Re: Oxygen sensor and check engine light


I am having a problem with my '97 Lexus ES 300 (with 148000 miles) oxygen sensors/(as indicated by my check engine light staying on).
It started when I changed the spark plugs and soon after driving off the (Toyota) dealership my check engine light came on. I immediately went back and was told that my front two sensors have gone bad – was also told that this could happen due to the new spark plugs.
I got the front sensors from Advanced Auto Parts (Bosch Premium Oxygen Sensor) since the Lexus/Toyota ones were significantly more expensive. My Toyota dealership said that putting in the Bosch should work fine.
After, however, installing the two (left and right bank) on May 14th, the check engine light came on again. This time the Toyota dealership said that (based on the diagnostics run by them) the front sensors are not working (the ones that I changed) and they also noted this: “Exhaust Gas Recirculation Insufficient Detected”.
Now, their suggestion is that I ought to replace the Bosch sensors with Toyota/Lexus original sensors and that ought to work.
Am I missing something here or is the Toyota dealership groping in the dark in terms of what is wrong? Can I drive my car extensively with the faulty sensors?
Sorry for the rather extended script…any and all response/s will be tremendously appreciated.
Thanks and regards.

Sensors monitor the cars exhaust. Sensors go bad. But a check engine light could be the sensors doing their job and pointing out a more deep seated problem. Since you just replaced the sensors there could be another problem causing the sensors to register. I think you need to dig deeper into this rather than just toss in a new batch of Toyota brand sensors.

Thanks UT…do you have any suggestions/recommendations as to what else I should look at? The Toyota place is quite happy simply running the diagnostics and when I asked them this same point that you have raised, they mentioned that Toyota/Lexus sensors should take care of this.

I’d suggest an independent shop in your locale that specializes in Toyota and Japanese cars. So many things can throw a check engine light, a cracked or leaking vacuum hose, bad exhaust or intake gasket, etc. If you hadn’t replaced the sensors already the dealer action plan might be OK, but it seems they are taking the 1st step in the process all over again. So, you pay a few hundred for their new sensors and what if the light comes on again in a few days or a month? If the dealer will guarantee this will fix problem and if light comes back on they fix it for free, then let them replace the sensors with Toyota brand. If they balk on a guarantee, then I’d try another shop.

It’s possible when the plugs were changed, a hose somewhere was knocked loose and/or connected improperly. New plugs wouldn’t or shouldn’t make a motor throw a code. But a faulty job by the mechanic could cause a code.

Service writers, the gate guards to the service department, seldom have any technical knowledge…

Please post the actual codes being stored…The EGR code is a separate issue…Cars don’t wear out one part at a time. They are cleverly designed so the whole thing wears out as a unit, multiple failures occurring over a short time-span is exactly what the designers were hoping for…

Uncle Turbo is giving you sound advise…

Thank you Caddyman and UT

I am attaching (as a word document) what I received from the dealership.

In order for the shop to ensure that the work they do is profitable they must be free to jump in and test, replace, re-test and replace at will with you responsible for the total of parts and labor. The shop cannot be caught in a situation where they are responsible for anything that cannot be billed even if it is a mistake. Dealership shops are under a great deal of pressure from both ends and more often than not the customer pays the tab. Good luck.

Common Problems That Trigger the P0130 and P0136 Code

Defective Oxygen Sensor/Air Fuel Ratio Sensor
Defective Oxygen Sensor/Air Fuel Ratio Sensor Heater circuit
Exhaust System Leak
Intake Air System leak (including vacuum leaks)
Low Fuel Pressure
Defective Engine Coolant Temperature Sensor
Defective sensor wiring and/or circuit problem
PCM software needs to be updated
Defective PCM

Common Problems That Trigger the P0150 Code

Defective Oxygen Sensor
Faulty Oxygen Sensor wiring or connections
Defective operation of the Fuel System

Common Misdiagnoses

Oxygen Sensor Sensor is replaced when the problem is a lean-running fuel system
Oxygen Sensor is replaced when the problem is faulty Oxygen Sensor wiring or connections
Oxygen Sensor is replaced when the problem is a vacuum leak or defective Mass Air Flow Sensor

Common Problems That Trigger the P0153 Code

Defective Oxygen Sensor
Faulty Oxygen Sensor wiring or connections
Exhaust System Leak(s)

Common Misdiagnoses

Oxygen Sensor is replaced when the problem is faulty Oxygen Sensor wiring or connections
Oxygen Sensor is replaced when the problem is a vacuum leak or defective Mass Air Flow Sensor

Thank you so…so much Caddyman.

I surely am curious in terms of one of the common problems as indicated by you: “Faulty Oxygen Sensor wiring or connections”. I now remember that sometimes my check engine light would go off and then come on again. I will definitely go back and ask them to check the connections; hopefully, it works!

Appreciate your input.

Your Toyota dealer violated the first rule of troubleshooting a new problem right after maintenance, go back to what you just did.

They may have used the wrong plugs, disconnected a wire or vacuum line and did not put it back or broke a wire or wires or tore open a vacuum line. It could be coincidence that you got a CEL due to the O2 sensors, but the odds are against it.

Thank you Keith…the only problem is that now they are not willing to check it again unless I change the sensors. Asking around for a more reliable (and trustworthy) mechanic.