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Sanity check my diagnosis please

posted May 20, 2016 05:32:55 by JosefMiller
2006 Toyota Tacoma with a 4.0L engine. Code in memory was P0158 B2 sensor 2 circuit high. I pulled up the PIDs for both rear o2s and they were 0.00v with the engine running. I then held the rpm at about 3000 and they began to show activity. I took a measurement on the power and ground on both of the rear o2s. I found 12v on both wires on each o2. I then went to the PCM and probed the control wire. It was a solid 12v (this is with a DSO) I cleared the code and tested again. Still no control. All powers and grounds on the computer tested and in spec. other test I did was ohm the heater and got 13.5 on both.

Am I missing anything? The only inputs for the heater I read about on Mitchell is engine running and battery 10.5v or more. I know it enters fail safe when a fault is detected so I cleared the code and had the same results. I also pulled the negative cable to clear the memory as well.

Recent repairs are power steering rack and timing cover gasket.
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7 replies
Inge_Jeppesen said May 20, 2016 15:10:50
Never mind the heater curcuit. This code is set when the pcm sees to high voltage on the o2 curcuit. I would monitor the pid closely from cold to warm. Did the dtc come back right away?
JosefMiller said May 20, 2016 21:44:18
They pid shows 0v until the exhaust gasses heat up the sensors. They they function as rear 02s would.

I can not look away from the heater circuit because there is no control on both banks to the heater.

I don't know why a heater code was set but that's where my issue is.

Also a p0606 code was set prior to this o2 code
JosefMiller said May 20, 2016 21:46:59
I know the computer will also enter fail safe and stop controlling the heaters when 02 faults occur. That's why I reset the memory and checked again. Still does not have control.

Yes the code is a hard fault
Inge_Jeppesen said May 20, 2016 22:25:11
P0158 is sensor curcuit high voltage b2 s2.

Are you sure the fault is with the heater curcuit?
JosefMiller said May 20, 2016 23:00:55
Yes the signal is fine with the sensor warmed up. When doing wiring checks on the heater as well that's when I found no heater control.
Tyler said May 22, 2016 00:49:08
Hey Josef! Any chance you could post some scan data with the O2's and A/F sensors? I know you mentioned that the sensor performs well warmed up, but I thought some data analysis might help.

It'd be really awesome if you could capture some data during a drive when the code resets. That way, we could ID exactly what the PCM isn't liking about the B2S2 performance.

I can say that I've heard of biased upstream A/F sensors causing this code, but haven't seen it personally. The A/F sensor becomes biased in such a way that it doesn't skew fuel trims, but does cause the downstream sensor to read too rich for too long, thus the code.

Any chance that there's a scan tool bidirectional function for the downstream heater? Just to prove that the PCM can still operate them. Toyota also has an excellent A/F and O2 sensor bidirectional test, which forces trims rich and lean without having to create vacuum leaks or use carb clean.
JosefMiller said May 24, 2016 18:40:38
I will post some scan data and look at those things Wednesday and post.

That's when I get the vehicle again.

Even if the drive was shut off because of the fault code. Wouldn't clearing it and starting the truck operate it for a little bit?
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