Engine light keeps coming back

The engine oil light of my Toyota Siena CE 1998 keeps coming back. After the garage replaced oxygen sensors and the catalytic converter, it came back. They replaced again the oxygen sensors, adjusted the distance of the catalytic converter, it came back. I took it to a Toyota dealer who diagnosed that the problem came from the catalytic converter. The garage said the new catalytic converter, a genuine Toyota part, is defective and replaced it again. Three weeks later the light comes back.

I informed the garage that the seat-belt light on the display panel has been on for years despite the fact that we all wear the seat belt the moment we get into the car. They do not think the display panel or wiring affects the engine light. So after almost a year, the engine light keeps coming back.

The garage has always been courteous. They honored the warranty and does not charge me more. I feel bad for them too and don?t know what else I could do. Any advice?


The engine oil light has nothing to do with O2 sensors, catalytic converters, and whatnot. I also do not understand the part about “adjusting the distance of the catalytic converter”. What in the world is that?
There has to be some misinterpretation of what has been said.

To be honest, I think you have a garage with no clue and they’re throwing parts at a problem. It’s also possible they’re NOT replacing things multiple times and simply BSing you.

My suggestion at this point, considering lack of details, is that you drop by a local AutoZone, Checkers, Advance Auto, etc. and have them scan the car. They will do this for you free and it only takes a few minutes. Post any results back here for discussion. And do not expect the counter help there to actually diagnose the problem; that is not their job nor should they attempt to do so.

find another mechanic. the one you are using sounds like they are exceeding their scope of mechanical knowledge.

If that light really is a oil light, then run from those mechanics that have been taking your money, you know more about it than they do.

On the other hand if it is a CEL (Check Engine Light) That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

 Those mechanics still don't know what they are doing however.  All the light can do is to point to an area that is showing something unexpected or out of the norm.  They then need to figure out what is causing that signal.

C’mon guys, the OP clearly means check engine light, not engine oil light. A common mistake. Everyone try again.

Thanks for your advice, gentlemen (or ladies, too).

First, by “engine light” I mean the “Malfunction Indicator Lamp” (the exact word in the manual) my apology if the terms are not interchangeable (I’ve been communicating with the garage under this term for a while and has not been corrected).

I took the car to Advance Auto for a scan yesterday following your advice. The result is “catalytic efficiency below threshold, Bank 1”. I was told that the front oxygen sensor was defect or installed inproperly. The code was reset (P0420). The lamp was off briefly, but lights up again this morning.

The people in the garage are young but have been willing to follow-up without charging me more (after I spent about $2000 on replacing the OS and pipes). If I go elsewhere now I’ll have to pay again.


Why is it that when the oxygen sensor does what it is supposed to do and identifies a problem, people want to replace it instead of looking for and correcting the real problem? There’s a troubleshooting procedure that should lead to the real problem, use it.

One area to check for this problem is a defective thermostat. If the thermostat is stuck partially open, the engine never gets up to full operating temperature. When this happens, the catalytic converter doesn’t come up to full operating temperature and this causes the cat to operate inefficiantly.



I got the car scanned and the code set. But the light came back the next day.

I gave the garage your suggestions. They said they’ve worked on all of these problems already. While promising to go over the list again, they don;t seem to be optimistic in finding new solutions. What happens to the car if I keep driving it with the engine light on? Someone says nothing would happen, the car won’t be damaged. If that is the case, why does the manufacturer’s manuel tell owners to bring the car to the dealer when the light is on?


You have two oxygen sensors pre converter, one upstream and one downstream. The upstream one measures the oxygen output from the engine. The downstream one measures the oxygen again and, if it sees no change or an out-of-range signal, trips a fault code in the computer. The code when downloaded indicates an improperly operating cat converter…however if the downstream oxygen sensor is bad it can actually be a bad downstream O2 sensor.

Which oxygen sensor was changed, the upstream or the downstream?

I was told both were changed.