So i was driving the 4runner (1994 SR5 4runner 3.0 v6) around the other day after she was sitting at for about a month not getting driven. And all the sudden my CEL came one, I pulled some codes and 21 came up - OXYGEN SENSOR SIGNAL/OXYGEN SENSOR HEATER SIGNAL. Has anyone else had this problem? Is it an easy fix or just easier to replace the 02 sensors and call it done?

 

Bump!! Anyone?

 

Check that the wires are intact first; not uncommon for them to touch the exhaust & burn through. But if you need to remove it, LUBE GENEROUSLY FOR DAYS with PB Blaster, then you'll probably end up cutting the nuts off with a Dremel, anyways~

Be sure not to damage the threads on the posts when you cut them off...

 

Disconnect the O2 sensor and check the O2 plug (engine side) heater wires (should be one black and one brown wire) for voltage when the engine is running. No voltage = wiring issue, possibly where the wires cross over the transmission. If you have voltage, the O2 sensor is likely bad.

 

Alright sweet thanks guys.

 

Quick question, when I go to check to see if there is voltage on the heather wires and there isn't, some one said earlier possibly over the tranny, would the wires be burnt though maby, would would be the fix for that? Find the wires and soder them together? Or krimp maby?

 

They may be rubbing on the trans and chaffed, and the heat from the trans also causes the jacketing to harden and crack which makes it easier to crack and chaffe. I'd slide some heat shrink on and solder before I'd crimp- unless it's a water-tight crimp.
With the V6, the crossover is another possible source of issue, like TNRabbit said.

 

Alright thanks for the info guys

 

So new update, i was able to disconnect the O2 sensor and i checked the voltage from the motor side and . . . . . . . . . . nothing. So i did what y'all said and i followed the wires going over the tranny and they weren't pinched anywhere or anything that i could tell. But The wires coming out of my EGR valve have come out of the connection and i just put the back in, but they might not be getting a good connection and i was wondering if this could be causing the CEL to come on and pull up that code?

 

Bumb with the new update, any new ideas?

 

start at the O2 sensor & check with a multimeter at each junction until you isolate where the break is located.