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"Service Engine Soon" light on a 2002 Mitsubishi Diamante


I have a 2002 Mitsubishi Diamante LS. Recently the “Service Engine Soon” light has come on and off several times and is now on all the time. AutoZone read the codes for me and told me that I have an oxygen sensor problem. I have 2 questions:

(1) Is there any way that a bad muffler can cause this code? I have a hole in the muffler that has gotten progressively worse about the same time that the light started flashing… it doesn’t seem logical to me that the muffler can cause it… but that’s why I am asking.

(2) assuming it is an oxygen sensor and not the muffler, how do I know which sensor is giving me the problem? Apparently there are 4 in this car… 2 in the manifold and 2 after the catalytic converter.

Thanks so much for any help you can offer!


You should get a code for the exact sensor not providing the signal the PCM is looking for. Not necessarily a bad sensor, but a sensor not providing a signal the PCM is looking for. It will say sensor 1 bank 1 or sensor 1 bank 2 or sensor 2 bank 1, etc. This will isolate the sensor. THe guys at autozone should know enough to give you that information. But wait a minute, maybe not. They do get training, but for many of them, it is all module training, and no hands on training. You might have a bad sensor after all, if you had someone experienced watching the cross counts in a “monitor” mode on the sensor, they can determine whether or not the sensor is bad. If it is totally dead, then yes, your sensor needs changing. This is why some mechanics get paid what they do, because they are more than parts changers. They have the ability to understand what’s going on with your engine, versus just reading a computer and changing parts that are suspect. While I’m on my soap box, let me share one more thing that grinds my gears: everytime I hear someone tell me they got their car fixed at the shop and paid $800, because the car computer and the ignition module went out, or the yada, and the yada (fill in your own parts) went out, I immediately suspect they threw parts at the problem until they found the root cause. Sometimes, but not often, one part can in fact, cause another to go out. But usually, it is a bad initial diagnosis, so the general rule is to say "yeah, the flux capacitor caused your widget-mabob to go out. Thank you for listening. (stepping down off soap box) That is all I have to say about that.

Can I assume that is a “Service Engine Soon” or is it really a CEL “Check Engine Light”?

Assuming a CEL then how about getting the actual code. It will be in the format [P1234]

How many miles on your car, has it been properly maintained as recommended in the owner’s manual?

Thanks for the responses. I am not sure what the difference is between a CEL and a “Service Engine Soon” light, but the light actually says “Service Engine Soon.”

The Actual code is P0155. The readouts did not give any information on sensor # or bank #.

There are about 70,000 miles on the car. I am the second owner and it has been properly maintained as far as I know.

I have a good mechanic that I trust, I just don’t have the $ right now to take it to him. I am trying to figure out whether I can keep driving for a while or whether I need to take it in ASAP. I’d rather not do more damage, but I am feeling the $ pinch.

Thanks very much for your thoughts!

Check out this link:

Note that it refers to an MIL which is a “malfunction indicator light” which will be the same as your SES and the same as a CEL (in this case).