To wire a test rig like this would you just use the switched wire from the pcm as the ground and not use the black/blue ground wire at all? Like I said, I suck at electrical work.

 

PCM expects to see voltage on that ground wire.....

 

Can you explain what you're thinking here as if I were a complete moron? haha.

 

The PCM will expect to see voltage on the wire, to verify the heater circuit is working, if it doesn't see the voltage, it will set a code for the heater circuit.

 

I meant what you're thinking more globally in terms of cause of failure

PCM expects voltage from the heater wire, or the heater control wire? Also, I'm just now realizing by looking at this wiring diagram that it appears the rear o2 sensor is not heated, because the only wires it has are power, ground, signal, and signal control.

 

If I remember correctly, heater circuit is powered via the ASD relay, which has to be working, or the truck wouldn't run. (It also provides power to the coil, and injectors.....) Since you are getting 12 volts IN, but only 2 volts out..... I suspect THAT is the problem. So, either a bad connection at the sensor connector, or, a failed sensor.

 

That's sort of the conclusion I came to, but it makes no sense. How is it possible that 2 NTK sensors, one brand new and one only a few years old, both have failed heater circuits...despite both having continuity when ohm tested...

Also, I'm not sure it's actually 2 volts OUT per say. The testing was done with the sensors not plugged into the harness (I don't have the skinny leads to test pin connectors while they're still pinned, I'd have to strip some off the cable to test). It's 2 volts hanging around in that 1 wire while unplugged from the sensor. Meaning the 2v is coming FROM the PCM on the Tan/White wire....right?

 

Ah, that changes things then. Use paperclip as a probe, works decent at least.

What to the pins in the connectors look like?

 

This is the style/shape of the upstream sensor. Round and grey. Pins look fine on the harness side.

 

Yes you need to use the switched grounds for the heaters to verify the PCM properly turns on the heaters. The black/blue is *sensor* ground, not for higher current heaters. BTW I just noticed an error in the wiring diagram on page 8W-30-17: Pin 24 on the PCM should read "signal" instead of "heater" and pin 16 is "heater control" not "signal control".

As I wrote before, and AFAIK the PCM has no means of checking the heater circuit directly. Nowadays electronic control modules can figure out if something is disconnected or a lamp is burned out but these PCMs are a 20+ year old design. P0135 code criteria is "The control module monitors how long it takes the sensor to warm up and start sending an adequate signal. The code is triggered when the sensor is taking too long to warm up."