Check Engine Light That Just Won't Go Away!

We have a '99 Lexus RX300 with 174,000 miles (the engine has 130,000). The check engine light has been on for 2 years. The first mechanic found it was an O2 sensor and said that we didn’t need to really do anything as long as the car was running good. So we didn’t. Apparently a new code appears when running a diagnostic for the evap. sensor or vapor canister…is that right??? We had the evap sensor fixed…or so we thought and than tried to have the vapor canister worked on but the mechanic said the light came on. Recently, the car has started lurching or losing power when it’s warmed up and when it’s accelerating. So, we took it to the Lexus dealership and 2 things were suggested 1) the vapor canister had been installed incorrectly and 2) sounds like the transmission is going. So I have 2 questions, I think, 1) What is going on with the check engine light? 2) Does this sound like the transmission is going? Oh and a third…What should we do???

Getting the check engine light to go away is easy - you can just have the bulb removed. But the check engine light isn’t your problem.

Since so much of your car’s operation depends on its computer the computer spends a bunch of its time checking up on different systems. It also requires certain info from other systems in order to do what it needs to do. When it detects problems it sets error codes and turns on the check engine light. This means that there is a problem and no good mechanic will tell you to ignore it.

At this point in time you have been ignoring it for so long (along with who knows what else) that helping you sort it all out by internet is probably impossible.

However, if you do want to give it a whirl then start by getting and reporting the exact error codes that are stored in the computer. They look like “P1234” - there are hundreds of these things, and normally multiple codes for the same systems. So referring to something like an O2 sensor or evap canister doesn’t help.

Is it possible that the lurching of the vehicle could be something other than the transmission than? I will check to see if we have the codes from all the work done. Thank you so much!

Yes, its completely possible that the lurching is an issue with how the engine is running. It may also be an issue of transmission control rather than internal to the transmission.

When you report back with the codes give as much info as you can on how/when you’ve done the basic maintenance - not oil changes - other stuff like spark plugs & wires, filters, transmission service.

Why was the engine replaced?

Ok, the code is P0446. We had a vapor canister installed but the function code reappeared, so the mechanic put back the old canister so that he wouldn’t have to charge us. This mechanic said the fuel pump tested ok on a cool engine. One thing I’m thinking is that we took it to the Lexus dealership after this mechanic and Lexus said the canister was installed incorrectly…I’m wondering if it was ever installed correctly?? Lexus had the same code, P0446 and they suggested replacing canister assym and vaccuum hose. Then they added the recommendation for a new transmission as well. We’ve had timing belt replaced, engine and transmission flushes, variable timing sensor replaced to name a few.

A couple more things I found…sparks plugs and valve assy, cam timi were replaced in 2006 because Lexus found that bank 2 vvt control valve was sticking (code P1354). The last trans flush that I can find records for was in 2008. I don’t know if we had one completed since that time. As far as the engine, it belonged to my father-in-law before us and I’m not sure why it was replaced.

Perhaps its time to get away from the dealer.

Is P0446 the only code you have right now? Its not going to make the car lurch or lose power. If they are telling you that you need a new transmission I assumed that you would end up with some transmission-related codes.

Have you actually checked the transmission fluid on your own? It should be at the proper level, a nice translucent red, and not smell burned.

The two things on the top of the list for lurching/power loss under acceleration are fuel pressure and exhaust blockage. It is certainly possible that its a transmission problem but I wonder what led to this conclusion.

You said your mechanic tested the fuel pressure static & cold. It ought to be checked hot and under load. Someone should also put a vacuum gauge on it to check for exhaust blockage - unless you have some more info about the transmission.

As much as you can’t drive around with the evap system throwing codes, there’s no point in putting money into that if you have much larger issues.

Thank you for all the advice! I took it to a new mechanic and the only code that is showing is the P0446…no code has appeared in reagards to a faulty transmission. I asked the mechanic to check the trans fluid before doing anything else as we don’t want to spend any money on the car if, in fact, the transmission is going out. I kind of had to pull teeth for him to do it, but he finally agreed.

Again, thank you!

P0446 is “Evaporative Emission Control System Vent Control Circuit Malfunction”.

Normally I’d agree with Cig that it would not cause lurching, but if the “malfunction” was of a nature that it prevented the gas tank from breathing in to replace the gas that’s being pumped out it could allow a vacuum to develop in the airspace in the tank sufficient to prevent the pump from being able to provide sufficient gas to keep the engine running smoth. That would cause lurching and chugging, and could feel ike a tranny problem.

Generally it’s a good idea to start by fixing whatever is causing the light, then see if the other symptoms are still apparent.

I’d tend to avoid any mechanic that told me to ignore a CEL because it was “only” the oxygen sensor. No good can come from that. Only bad. At this point i’d recommend finding a reputable local shop, telling him the whole story, and having him diagnose and fix eth cause of the CEL. If your other problems don’t then disappear, you’ll have lost nothing. But I’ll bet they will.

It did end up being the transmission. I took the advice of cigroller and asked them to check the possible transmission issue first and the fluid was in fact a little brown and burnt smelling. We ended up selling the car to this mechanic. He seemed to be honest, but I guess you never know.

Just for future reference, this transmission problem might have been avoidable if you had changed the trans fluid (and filter) every 30k miles/3 yrs. If you buy a used vehicle, unless you have documentary proof of this type of transmission service, you need to get on track with that type of servicing.

I have always followed this schedule with my transmissions, and I have never needed transmission repair, even on cars with mileage in the 170k category. On the other hand, we get regular posts in this forum from folks who had to replace/rebuild their transmissions any time after 90k miles, and it has always turned out that these transmissions were not serviced as I described.

Timely maintenance is invariably cheaper than the repairs that result from lax maintenance!