The husband of a friend of my wife was over today for a BBQ and related to me a problem with his 238,000 mile 2000 Sienna. Now he almost zero knowledge on cars and I had to show him how to do an oil change on a BMW 538i. So this Sienna threw a P0171 code a week ago. First guy was a mobile mechanic who said it was the MAP sensor. Yeah, right. Yet he had the MAP sensor replaced. Runs Ok but of course a code shows up later after running and resetting. Brings in to Toyota Pro (independent) who tell him he has a problem with bank 2 sensor 1 now. They replaced the sensor and guess what. A day later a code is thrown again. Brings back to them and tell him he has another problem with, you guessed it, the MAP sensor. They did check his engine out for any vacuum leaks using smoke.
Getting good. So he buys another new MAP sensor and has another (third) mechanic install it. Once again a few days later the next new code is P0430 which he got because he borrowed a scan tool. Calls the same mobile mechanic says it is an air/fuel sensor. He gets that replaced. After driving 56 miles the fourth code is thrown. P0420 which he check with the scan tool. He then goes out and buys a new sensor for downstream now. It is installed. Code is erased but of course comes back. Goes to a muffler shop and they say he needs a new converter immediately. Maybe so but they did no testing to prove their diagnosis correct. Easy enough to check the output of the O2 sensors when hot and running at 2000 rpm. Also easy enough to check the inlet and oulet temperatures of the converters.
Now it is quite possible it could need a new converter since almost everything else was replaced by throwing stuff at the car. The engine itself is running fine except for the CEL. I do my own work and am not about to deal with this as I have 10 cars to deal with. Just irritates me that mechanics jump to all sorts of conclusions and I can't recommend a good mechanic. Being a doctor I have a procedure I have to follow when a condition is presented and I have other possibilities in the differential diagnosis unless the condition is blatantly obvious like you have a nail in your eye so no wonder it hurts. Anyway he is wondering who to go to next but he now knows almost as much as I do on the subject as he is right here. Most likely a new cat but at least someone who can prove their diagnosis. LOL, I told him to quiz mechanics now... that should be fun.
Getting good. So he buys another new MAP sensor and has another (third) mechanic install it. Once again a few days later the next new code is P0430 which he got because he borrowed a scan tool. Calls the same mobile mechanic says it is an air/fuel sensor. He gets that replaced. After driving 56 miles the fourth code is thrown. P0420 which he check with the scan tool. He then goes out and buys a new sensor for downstream now. It is installed. Code is erased but of course comes back. Goes to a muffler shop and they say he needs a new converter immediately. Maybe so but they did no testing to prove their diagnosis correct. Easy enough to check the output of the O2 sensors when hot and running at 2000 rpm. Also easy enough to check the inlet and oulet temperatures of the converters.
Now it is quite possible it could need a new converter since almost everything else was replaced by throwing stuff at the car. The engine itself is running fine except for the CEL. I do my own work and am not about to deal with this as I have 10 cars to deal with. Just irritates me that mechanics jump to all sorts of conclusions and I can't recommend a good mechanic. Being a doctor I have a procedure I have to follow when a condition is presented and I have other possibilities in the differential diagnosis unless the condition is blatantly obvious like you have a nail in your eye so no wonder it hurts. Anyway he is wondering who to go to next but he now knows almost as much as I do on the subject as he is right here. Most likely a new cat but at least someone who can prove their diagnosis. LOL, I told him to quiz mechanics now... that should be fun.