Heater circuit intentional shut down on Toyota

Looking for info if anybody on here is familiar with Toyota
2003 Sequoia 4.7

P0037
Tests done; heater circuit voltage drop test done checked good KOEO voltage and KOER voltage
Sensor ground to ground test 20 mv
Sensor signal test touching battery positive with my finger I can see the computer react on my scan tool

Everything to me tested good on the wiring side so I replaced the sensor code came back a few drive cycles later
What did I miss ?
What are the parameters for this code?
Is the computer intentionally shuting down the heater?
Ps after the fact I noticed the connector does not click at all when the connection is made

Any thoughts are appreciated
Thanks in advance

Do you have 12v on the heater power wire? You did a check of the 02 sensor signal wire but not the 12v to the heater. If no 12v check fuse and wiring.

Yes sir I checked the heater circuit voltage KOEO Cycled the key Cycled the key then checked it again with the KOER both times I had battery voltage (I was using a load pro because I was having trouble getting a good back probe)

Service info says this code sets if the heater current is less than .2A or more than 2A.

It wouldn't surprise me if the computer was intentionally shutting the heater down in the presence of a current heater code, but that doesn't explain why the code came back. Were you ever able to get the connector to latch in correctly?

P0037 is for the B1S2 O2 sensor. No offense meant here, but did you replace the downstream sensor on the drivers side?

Yes sir I replaced the down stream on the drivers side. I back probed it this morning on the sensor side of the connector, 2 black wires had no voltage I cleared the code and cranked the car. 13.87 v immediately shows up, I looked at the live data for this pid at the same time. The data voltage stays at .095 mv but if I snap the throttle I can drive the sensor rich to.800 mv then it goes back to .095 mv. I'm concerned about my cat being bad.

mullins7 wrote: Yes sir I replaced the down stream on the drivers side.

Sorry, had to ask. :blush:

I back probed it this morning on the sensor side of the connector, 2 black wires had no voltage I cleared the code and cranked the car. 13.87 v immediately shows up

Are you sure that's a function of the code clear? Because I see that the heater power comes from the EFI 2 fuse. It's possible that fuse is only powered with the engine cranking or running. Given that the same fuse powers all the other O2 heaters, EVAP solenoids and the MAF, I really doubt that it's the power side of the circuit that's being taken away.

This is a shot of the OE diagram, for reference:



We know that there's voltage at the heater, so now we need to know about ground. Backprobe the white/red wire, clear the code and check for voltage with the engine running. Or, connect a test light from B+ to the white/red and see if it shines after a code clear and startup.

I looked at the live data for this pid at the same time. The data voltage stays at .095 mv but if I snap the throttle I can drive the sensor rich to.800 mv then it goes back to .095 mv. I'm concerned about my cat being bad.

Given that you were working with a cold engine, and that Toyota doesn't use any bias voltage on their O2's, that only suggests that the O2 sensor circuit is good. A failed catalytic converter won't cause this code.