Differences in heated O2's

[turbo_bu]

I wanted to see if anyone has played with the different types of heated O2 sensors (e.g. - grounded vs. isolated). I have been researching doing a swap with either a 512 kB (blue/red) or a 1 MB (blue/green) LS1B PCM, and noticed that there could have been several different HO2S configurations. Specifically, this will be a non-emissions swap, so I don't need the secondary O2's, just the primary. From looking at the 512 Kb wiring diagrams, it shows that there were several different ways GM hooked up the O2's. The 1 MB PCM's appear to have carried over the isolated grounded O2's.

Some very good back ground information on this topic is found on the lt1swap.com website (www.lt1swap.com\vortec_o2_sensors.htm). But one thing it doesn't talk about is if it really matters or not. Specifically, the thing I noticed was that the 2002 Camaro (F-body) O2 sensor uses +12 V and chassis ground to power the heater. The other iterations of O2 heater circuits use either +12V and PCM ground to control the heater circuit .... or power and ground both hooked up to the PCM.

Since this is a swap, and I am making my own wiring harness, couldn't I just use +12V and chassis ground to hook the heater portion of the O2's? Or do I have to use the PCM to help control the heater circuit? For the Camaro O2's, (I believe those are the grounded type) you can do this since that's what the factory did.

But if you happen to have the isolated grounded O2's, then do you have to use the PCM to help control the heater portion? Does the PCM really care? Doesn't it just want to see the signal swinging back and forth above / below 0.450 volts?

Can you hook up an isolated grounded O2 to just +12V and chassis ground and get it to work?

Or maybe you can hook up a case grounded O2 to a 1 MB PCM (those appear to be all isolated grounded) using just =12v and chassis ground. Again, as long as the actual O2 signal wires are still connected to the PCM, would it still work?

Going forward, I was hoping that I could just standardized on a type of O2, to make that part of the wiring easier. That way instead of having to worry about which kind of O2 it was, and / or what the OS I was using was setup for, I could just hook them all up the same. If you have played with this and can provide any insight, I would be very grateful.

Thanks,

[joecar]

...

Since this is a swap, and I am making my own wiring harness, couldn't I just use +12V and chassis ground to hook the heater portion of the O2's? Or do I have to use the PCM to help control the heater circuit? For the Camaro O2's, (I believe those are the grounded type) you can do this since that's what the factory did.

...

This is what I would do (switched/fused +12V)...

[turbo_bu]

joecar,

do you know if I could do the +12V / chassis ground setup with the isolated grounded O2's too? Or is there something special about the way that the heaters in those work?

[joecar]

joecar,

do you know if I could do the +12V / chassis ground setup with the isolated grounded O2's too? Or is there something special about the way that the heaters in those work?

The F-car NBO2S are isolated ground, and the F-car wiring diagram shows +12V / chassis ground, see attached:

[joecar]

I'd have to look more closely at some truck wiring diagrams.

[turbo_bu]

The F-car NBO2S are isolated ground, and the F-car wiring diagram shows +12V / chassis ground, see attached:

That's one of the things that has my somewhat puzzled. I originally thought the F body narrow band heated O2's (primary O2's before the cat), were case grounded from looking at the wiring diagram. But the connector is a square 4 pin.... which could mean they were isolated grounded.

I guess this is where I was looking for some clarification from others who had messed with this. Is there any downside to hooking up your heater circuit to just +12V and chassis ground? My guess is that having the PCM in the loop can help to regulate the current (the power) of the heater to try and maintain a more constant temperature (????) which might help out with getting a better reading from the O2 (????) This of course is just a theory... But was hoping others could help shed some light on the subject.

Thanks,

[joecar]

I don't see any problem with that (heater to +12V/ground).

Later cars (GTO onward): the PCM does in fact control the heater current just like you said.

I found 2 flavors for 2002 C-truck (Sierra 2WD 6.0L), see attached (now I'm even more confused than ever, lol).

I would temporarily wire to switched +12V and ground, and see if they work ok, and if they do make the wiring more permanent.

[Highlander]

I've grounded the isolated ones when converting from 1mb to 512kb without any i'll effects. YMMV

[RADustin]

can anyone confirm that on the OSs that provided power or ground the O2s, that the PCM also monitored this voltage and this is how it throws a P0155?

So basically if you have an aftermarket harness that provides say chassis ground with keyed 12 volts to the heaters, then this could be a cause of P0155?

[joecar]

Yes, correct, the PCM monitors the heater circuit and if voltage/current is not correct it throws the DTC.

On GM, typically the PCM controls the heater's ground, so this is where it is measuring voltage/current.

see diagnostic procedure here (basically, if wiring checks out ok then replace the PCM): http://www.gearchatter.com/viewtopic10710.php