The Toyota Highlander and its phantom lean codes

With how many systems there are in a car nowadays and how much they rely upon the operation of the other systems around them, fixing check engine lights can be a real pain. Every car is different, every manufacturer does things differently and the electronics are always changing. Take this highlander for instance. Customer says "Ever since I jump started my tractor with my car this check engine light has been on. My cruise doesn't work so I would like to get it fixed." Thankfully this customer has been down this road before on this car and knows the cruise problem is related. They know I am a big Toyota fan with dozens of them at any given time being driven by my family or in my current collection. How hard can it be?

It has lean codes for both banks. That can be caused by any number of things from the air filter, the beginnings of oxygen sensor issues, exhaust leaks before the AFR sensor, fuel with too much ethanol in it, dirty mass air flow sensors, the list goes on and on. It is always good to see what the computer says about any code with the Freeze Frame data it stores as well as observing the sensor data as well as the Short/Long Term Fuel Trims. Hooking up the Top Don Diagnostic computer, in this case, did not tell us anything helpful. The air filter is clean, no exhaust leaks, no symptoms the customer noticed, nothing... From the freeze frame data to the current sensor readings everything is where it is supposed to be. I find it to be best practice when things like this happens to clear the light, drop some ethanol free fuel in the tank, and see what happens over the next week.

Three weeks later the customer stops by and says that the light is back on again. Again all the same things reported by the computer. There are no TSBs, no reflashes for the engine control module, none of the lesser common related issues. They have been filling up at different gas stations every time and have not noticed any issues in drivability. It is so hard to find problems when it seems like the computer itself doesn't even think there is a problem... Sometimes you just have to wait for things to get worse before they become easy to find. It goes on like this for some time with them stopping in once a month to get the light cleared. The problem doesn't really bother them, they live practically next door and they are always driving by when we are open.

I finally get some free time and start searching around on the internet to see what they say. Thankfully there are forums for every single kind of car and they are often filled with people whose sole care in this world is their own specific generation version of a specific car. All their problems and efforts are focused on one platform even if there is a lot of noise you have to sift through in order to find some real truth. I just so happen to stumble upon a thread related to the purge valves on this specific model. Apparently they have this known glitch where every so often they get stuck open and the only indication of a problem at all is that the car stores lean codes (instead of purge flow codes you would expect to see on any other vehicle). I spent some time going through other threads about lean codes and got a lot of people talking about much of what had already checked out.

I order a new OEM purge valve and asked my customer to stop down once it was delivered. I install the part, clear the DTCs and tell them to let me know if they still have a problem. They of course wondered what the cost was and I told them we would figure that out once we are sure this even solved the problem. It was, after all, just a hunch based of some information that might not be accurate that I found on the internet. 2 months later with no sign of the code coming back we could be relatively certain the problem was fixed and the bill was taken care of the next time they came in for regular service. Interesting enough for you?

(Still have to lookup the year again since its not in my brain anymore)