ksmxlls

Hey CL,

I have been having this problem with all 4 of my o2 sensors not reading at all, About a couple weeks ago me and a friend that used to be a tech at toyota replaced the knock sensors in my 2001 Gs430. The sensors ended up being bad but they were completely out in the first place. This problem didn't stop the car from driving as long as I didn't push it hard. While doing the knock sensor job I have a second battery in the car for my system and the positive wire that I have running directly off the alternator to the battery touched the wall of my car (Ground) and it blew the alternator fuse in my car. I went and replaced the alternator with a sequoia alternator and put a new fuse in it. After the entire job was done I went to start the car up and It ran like complete crap So I put my scanner on it and I only got codes for the bad knock sensors but looking at the live data for my car it showed it was always in open loop and none of the oxygen sensors were reading at all. I figured the open loop fuel tri was because the oxygen sensors weren't reading.

So I started diagnosing the car as all of my ground wires were connected and and all of my connections inside the bay was connected as well, I replaced my downstream sensors as those are the easiest and they were still showing 0v. I checked all the fuses in the car and non of them were blown. I'm currently stuck on what to do now. has anyone gone through this problem before. Car has 278,000 miles btw and ran like a perfect lexus before we went to change the sensors.

Alphaman19

I'd use a multi-meter to at least check that there is at least continuity between thru the two ground connection on the o2 sensors.
Just unplug and see.

There are a few vids on youtube on how to diagnose them on a bench. Of course you'll need to take them (up stream ones) out but it's not that hard to do.

But my money is on the fact that you likely fried something with that stereo setup you had.

Good luck

ksmxlls

Yea that was my guess that I fried something with the system, Just trying to get some feed back on exactly what controls the oxygen sensors. Going to check it once the rain slows down. And thanks

eicca

Are you getting fuel trim readings?

I had a similar problem, all of my O2 sensors would flatline randomly but simultaneously, and it would run super rich. I replaced my EFI fuse and the problem went away, even though the old fuse seemed good. Not only did a new fuse fix my O2 sensors, but my transmission no longer has a slushy shift between 1 and 2. Nice and firm again.

As a very temporary test, bypass both the fuse and the EFI relay with some jumpers to ensure that proper electrical flow is getting to the ECU. Those engine computers will do very wonky things if the voltage gets even just a hair low.

Also check your coolant temperature sensor. If that goes, and the ECU doesn't know the engine is warm, it'll stay in open loop (I think).

ksmxlls

So I didn't realize that the connections for coil #7 got disconnected and I had to re pin them. Once I did that the car started reading the o2 sensors all of a sudden. it was kinda weird. I just have a lean issue now but I believe thats from not replacing the intake manifold gasket so I have one on order and when it gets here I'll just have to take the manifold off again to replace them.