'99 V6 1MZFE Oxygen sensors show voltage when disconnected

[uconnkoala]

'99 V6 1MZFE

I have been troubleshooting P1133 and P1135 on my car, which leads me to the oxygen (air/fuel) sensors.

In order to isolate what was wrong (I don't believe the OBD-II codes), I disconnected the 2 sensors on my exhaust mainfold before the cat.

However, when I hook my OBD-II scanner to read the voltages of the disconnected sensors, they still appear to be working:

B1S1: .66V (does not change)
B1S2: 0V-.85V (seems to vary with RPM)
B2S1: .66V (does not change)

My question is....WTF ???

Why is there a voltage reading with the sensors disconnected ?


This also leads me to believe the problem might not be with the sensors themselves.

Anybody seen things like this before ?

[BadChicken]

never actually took the time to look at it I guess. If I was you I would just replace Bank 1 Sensor 1 and be done with it. From what i've seen working for a dealership for the past 2 years, Toyota doesn't have to many wiring issues. Its usually the sensors themselves that are at fault.

[ASG14]

I just had to replace the O2 in my rear bank on my '96 with 92k miles. Fixed the CEL. And better mpg.

[uconnkoala]

Its entirely possible I'm an idiot

Details to follow.....

[uconnkoala]

I guess I'm only half an idiot

The B1S1 and B2S1 sensors constantly read .66V, so the computer didn't pick up on the fact they were busted, because .66V is a valid voltage for an air/fuel sensor.

The Haynes manual is wrong about the voltage range of the California air/fuel sensor, and the engine models it applies to. Always check under the hood (wire colors and stickers) before believing the generic manual. My Camry is a V6 '99 with Automatic Transmission. By the Haynes book, it says I will have Federal Emissions (so I'd have to use an oxygen sensor), but under the engine it says California emissions (which means an air/fuel sensor).

So I replaced the B2S1 sensor, and now I get a voltage range while driving.

Next job - replace the B1S1 sensor (next to the firewall)

I was able to reach B1S1 with my arms after taking off the intake plenum, but I'll let you know if I have to climb under the car to get a wrench on it.

I think the air/fuel sensors have been bad for a while, but no codes had been set until now.

I guess its a good idea to check for voltage ranges, and not just the fact the sensors are throwing a signal.

[uconnkoala]

Replacing with parts:

Denso 234-9007
Denso 234-9009

[BadChicken]

the rear bank o2 sensor isn't that bad, but I guess I'm use to using a lift to get under the car too. Little hands help alot, good luck

[BadChicken]

the rear bank o2 sensor isn't that bad, but I guess I'm use to using a lift to get under the car too. Little hands help alot, good luck

[ASG14]

Well, it;s a bitch to get to the rear bank O2 while it;s on the ground, haha. I picked up and O2 sensor socket (yes, there is actually a SPECIAL socket, haha), and hooked it to a 2ft breaker bar. Took a while, but I got it.

I got the sensor from the dealer.

[BigPete]

Originally Posted by ASG14

Well, it;s a bitch to get to the rear bank O2 while it;s on the ground, haha. I picked up and O2 sensor socket (yes, there is actually a SPECIAL socket, haha), and hooked it to a 2ft breaker bar. Took a while, but I got it.

I got the sensor from the dealer.

I had to do the same thing a few years back. Getting my arm up into where the rear sensor is was a real pain, especially when the exhaust was still warm. That socket adapter for 02 sensors really help.

FYI, it you just happen to strip the threads on the manifold trying to get the sensor out, you can always rethread it with a spark plug tap/dye.

[uconnkoala]

I ended up using a 22mm wrench that was about as big as my arm

Seemed to work OK