I’m eating crow today.
A couple pages back I spoke about my friend’s super clean FJ that had thrown a bank 2 lean code and a A/F sensor slow switching code. The dealership said they found transmission fluid in the harness at all the O2 sensors and at the ECM. They wanted over 5k to fix it but they never mentioned how they would prevent this from happening again. My friend and I were pretty suspicious with their diagnosis so he told them to just put it back together and picked it up. We cleaned the MAF, since the first and only check engine light was caused by them leaving the air filter lid and air filter completely off. I also pulled apart a couple transmission connectors and rear O2 sensor connectors but they were completely dry.
That FJ was running perfect until last week when the CEL came back on. The FJ was running smooth but the gas mileage had really gone down. He brought it to my house for me to look at and finally this week I had a chance to check it out. Hooked it up to TIS and found a p0171 bank 2 lean code like before. I also noticed the #2 long fuel trim was in the 30s. Thinking along the lines of the MAF still dirty, I cleaned it but that didn’t help. I swapped the MAF with the one from my 4th gen, that wasn’t it either. I finally pulled the bank 2 A/F sensor and much to my surprise, there was a little bit of oil in the connector. I pulled the other A/F sensor and found oil in that connector as well. I swapped the sensors from side to side and took it for a test drive. The lean code followed the sensor but it also triggered a A/F sensor heater circuit open code. I pulled that sensor and checked for continuity across the heater circuit and found it open. I swapped in a A/F sensor from my 4th gen and the FJ runs great with no codes. Cool, a new A/F sensor will fix the codes (hopefully) but where is the oil coming from?
I pulled apart the transmission control connector and found the source of the oil. This connector has a bunch of oil in it, definitely transmission fluid. So, it appears the dealership was, partially, right. I haven’t checked the ECM yet, hoping to tomorrow, and I still need to check if the transmission vent is actually plugged. I’m doubting that the vent is actually plugged since this FJ is pretty clean and pampered. My friend needs the FJ back so I’m installing a new sensor and hoping for the best. In the meantime I’ll research what is needed to correct the problem. For the hell of it, I popped off the trans control connector on my 4th gen and unfortunately found a little bit of oil in there as well. It doesn’t seem to be near as bad as my friend’s FJ but it’ll probably get there over time. Now to prove that no good deed goes unpunished, I went to re-install the A/F sensor back into my 4th gen but I noticed there was a little oil inside the connector so I sprayed it out with electrical contact cleaner and blew it out with compressed air. Now I’m getting an A/F sensor heater circuit open code on my 4th gen. Pulled the sensor and sure enough, the heater circuit is open. So either moving the sensors around (I was pretty careful with them) messed them up or the contact cleaner in the connector somehow fried the sensor. Either way, looks like I’ll need one as well.
So now, I’m a believer in this problem. With all the FJs, Tacomas and 4runners out there, I can’t believe we don’t hear of this problem more. So does anyone know what I need to fix both the FJ and my 4runner? I’m thinking the FJ will need the transmission connector and wiring harness at least. My 4runner will probably just need the connector on the transmission. Here’s some pictures.