Ive been trying to diagnose why i keep getting codes P0157 (low voltage bank 2 sensor 2), and P0137 (low voltage bank 1 sensor 2). These two are the usual ones, but i've also had P0158 (high voltage bank 2 sensor 2), and . The first time it happened, the car sat at an angle through a downpour. I went to start it and water came out of the tailpipes, then the code. Replaced that and it went away. It happened again on bank 2 and after i replaced that one, it went away. Was off for a good while but came back and i dont know why. I feel like its water related but cant get it to replicate; it started raining on my way home today. I erased the codes before driving, drove, it started raining, and no codes or CEL came on.

Things i have done so far:
- I have replaced both sensors (Denso). No twists in the wires.
- had an exhaust leak test done (only leak found was at junction between cat and exhaust)
- replaced gaskets
- Did CEL memory erase (some post showed disconnecting battery and pulling two fuses)
- Roof rack clean with lawnmower wire (i got the wire far down both holes but never saw it come out. My floor boards have never been wet though so i dont think its leaking into the cabin at all).
- Loosened and retightened exhaust bolts

YES i have read other posts. A LOT of other posts, but those are issues that others have had with aftermarket headers and extensions, which i don't have either of. Does have catback exhaust. Ive been erasing the codes with OBD2 reader, but it comes back. Its weird though, because when i erase the codes and drive the car, no codes. Its only when i shut it off, then restart, and about 3-4 miles later the CEL comes back on. I saw in a different threat that maybe its a wiring issue (looks like some aftermarket header setups had people hard wiring things into the ecu) but i looked at the ECU and dont see anything hardwired in (pic below) but i also dont know what im looking for. I also included pics from the code reader test

 

These are heated sensors. If the heater isn't working correctly, they'll fail every time. The ECM provides the power to the heater circuit to maintain a temperature range acceptable for the sensor to operate. If it were mine, I'd suspect the ECM first, but I'd check the wiring before assuming it is good. I worked on a GS F with a similar problem, and the root cause turned out to be the ECM, but we confirmed the wiring was good before swapping the ECMs.

As I understand it, ECMs for the IS F may be difficult to obtain, so troubleshoot the wiring first. Post up your model year and I can point you to the connectors and pins you need to check on the ECM.

 

Bro I've been waiting for you. It's an 08.

 

Here's the drawing with the wire colors. You should be able to isolate the wires you need to check with this information.

 

I dont know how you know all of this but the community is blessed to have you. Theres a lot I can do around a vehicle but electrical has never been one of them so this took me a bit to decypher. Basically, check pins 3 and 4 on connector A6, and pins 26, 27, 28 on connector E3. I cant make sense of the color diagram though.

As for actually checking the wires/pins, use a multimeter correct? Any special tips on how to do that?

 

I've been working with electronic systems for more than 53 years, and grew up around dirt track racing. I've learned a lot about how cars work over those years.

If you're not comfortable with electronics, enlist the aid of someone who is. Yes, you have the right idea, but you would be wise to have someone more familiar with this assisting you if you can make it happen.

 

You figure it out, and if so, what's the deal?

 

Dude, no.

Took it to Lexus. First hour was $237. Told the dude the problem wasn't the sensors and to check the connection at the ECU. He told me he preferred not to tell the tech that because if he did, the tech would be all over the place, the tech needed to go in order, and IF the tech asked THEN he would tell him everything I did up to that point. Got a call later with the service dude trying to walk me into/authorize another 2 hrs. I asked why, and he said the tech said he needed to remove the seats to check the connections. I spent a good 10 mins telling dude the seats didn't need to be removed and to pull the carpet back and he kept pushing back so I said screw it, put the car back together.

Took the car to a different place. Apparently I was missing two screws on the driverside connection from cat to x pipe. He told me that would fix the problem, I questioned him and asked how two screws missing from only one side would cause codes on both sides. He said let's try this then come back if it doesn't work. It didn't work. Went back, and he said to give him 2 days with the car so an electrician could check it. Dropped it off on a Fri morning, and sat morning got a call. Dude said to come pick it up cause they couldn't get it. I asked what they did and dude was kind of dodgy in his answers. I go in person and he said they hooked it up to a machine (which I told them not to do cause I already knew what the issue wasn't), said a random code would pop up that identified the car having an aftermarket exhaust, then said his electrician just didn't want to do it. He then recommended I go to this one specific area in town and look for a 70-80 yr old Korean, because they're good at diagnosing things like this.

 

That's a bummer! Good luck tracking it down and circle back when you figure it out.

 

Or make a road trip to Atlanta. We could probably have you fully diagnosed pretty quickly.

 

Update:
Took it to Toyota. They confirmed it is the ECU.

 

That doesn't say much. What did they check to determine this?

 

I don't know. But, I was explicit in telling them that I wanted them to check the pins related to the specific O2 sensors where the harness plugs into the ECU. I'll assume they started there because it wasn't long after I gave the directions that I got the call with the diagnosis.

 

OK. When I found a problem with a GS F, it was the heater circuit voltage that was missing at the output from the ECM. It is certainly possible the device responsible for heating inside the ECM failed. That's definitely what happened with the GS F.

 

Stupid question but did you check fuses as well? Few months ago on a rainy day I started getting downstream O2 errors and I knew right away what it was because I've been doing my own exhaust for past year or so and o2 sensor wires were getting quite a bit of rubbing and pinching every time I was working on it (because I didn't want to remove o2s every time I am making changes, which was fairly often).
The next day I cold started the car and while checking sensor readings I was wiggling wiring where it exits the sensor when suddnely engine came to a dead stop. This confirmed that the wires are messed up so I disconnected the sensors, restared the engine and took off since I was already late for work. Right away I noticed the car is running very very strange, connected the obd and my MAF reading was super low and other readings were messed up. I pulled up on the side of the road, and found that couple of fuse (s) have burned out. Can't remember which one(s) now but I think one was EFI2 since I assume car wouldn't even start without main EFI fuse. Replaced the fuse(s) and it was all fine again (except O2 codes of course since they are disconnected). Later raplaced O2s since I have spares and no issues. The wires on old ones were actually exposed so heater probably shorted when I wiggled the wiring. I don't think this is the case with issues you described but it might lead you onto something else too. I would at least hope fuses protected the ECU.


If it's indeed ECU related issue, it's probbaly worth sending it to some electrician experienced with PCBs and circuits such as ones in ECUs. I am sure you can find someone around you but if not, I can talk to my buddy I work with who is experienced with this kind of stuff. He has a youtube channel related to circuit board stuff and is also a Toyota guy. Here is a video of him replacing capacitors on my JZX110 MARK2 The only thing is, if he can do it, you would need to ship it to Japan. Alternatively, I could source you a good used ECU here in Japan for fraction of a cost of new one (you don't need anything other than ECU, paper clip and 30min to change it, no need for different lock / keys etc) but not sure how much the shipping would cost so it could offset a price quite a bit compared to what you can find used locally. Also note that JDM ECUs have 180kmh speed limit unless it's tuned out (which it isn't in 99% cases since everyone use piggyback devices such as HKS VAC) so you would need a option to solve that. I have spare ECU that I would let go for 300$ but it's tuned on a unknown setup and my car didn't like it too much so it probably wouldn't be of much help to you either. No issues when normally driving but not quite "there" when you punch it. It does have speed limiter tuned out though. Maybe can be used for spare components to replace in yours. Just throwing any possible options out there since price of a new one is quite a racket.