How Do I Test The O2 Sensor Heater Circuit?

[Rcroane]

Hi folks...can someone tell me how I can test the heater circuit on the harness side of my 1/1 O2 sensor using a multimeter? I think (but need confirmation) that I put one lead on the positive battery terminal and the other lead on the ground pin of the harness connector. Am I then looking for the MM to read 12V?

Thanks.

 

[Jerry Bransford]

If you're having trouble with the heater circuit not showing ready for a smog test check this thread out. There is a problem with that circuit in newer TJs like yours and there's a TSB for it.

https://wranglertjforum.com/threads/oxygen-sensor-heater-issue-cant-pass-smog.42268/

And yes the O2 heaters run on 12vdc.

 

[Rcroane]

If you're having trouble with the heater circuit not showing ready for a smog test check this thread out. There is a problem with that circuit in newer TJs like yours and there's a TSB for it.

https://wranglertjforum.com/threads/oxygen-sensor-heater-issue-cant-pass-smog.42268/

And yes the O2 heaters run on 12vdc.

A little background and maybe it's not a big deal at all. I had a P031 code a couple weeks ago. As a first step, I decided to replace the 1/1 sensor. The code hasn't come back (pending or confirmed), but it's only been a couple of weeks. I have a pretty decent scanner (Actron ) and that's what I've using to test for codes. But, I've also got one of those OBD dongles and it shows that Oxygen Sensor Heater test was available but not complete (showing a red X). Of note, the dongle also shows that "this vehicle IS ready for emissions testing". I also tested the old 1/1 sensor and it was showing 3.8 ohms when I put my meter on the two heater wires. From what I read, this means that the sensor probably wasn't bad to begin with. So, since it doesn't appear that the old sensor was faulty, I guess I'm kind of expecting that I'm going to get another P031 code. Sorry for the long winded response!

Edit: I did get 12+ V when I tested the harness side of the circuit. I'm actually going to get my emissions test tomorrow. In Virginia, we have those drive by testing boxes that sit on off ramps. I have know idea how they are able to test in a 1 second drive by, but I fully expect to pass.

 

[Wtrask]

I’ve got to the point where I just replace all of them whenever I get a code. They are like tune up parts in my Jeep.

 

[OldBuzzard]

... the dongle also shows that "this vehicle IS ready for emissions testing" ...

Your reader sounds like mine: an OBDLink SX Scan Tool (dongle) with OBDwiz software. And mine shows the same Oxygen Sensor Heater test as not complete.

A strange quirk (sloppy programming) is that on the Monitor Status Report it shows "This vehicle is ready for emissions testing" but on the larger full Diagnostic Report it shows "This vehicle is not ready for emissions testing".

We have those drive-by testing boxes in Colorado too. I'll try to find one when mine is due (it's a ways off). If I have trouble with the emissions folks, I'll rewire it with TSB 25-001-07 (Google/Duck/Brave it, you'll get lots of links).

 

[Rcroane]

Your reader sounds like mine: an OBDLink SX Scan Tool (dongle) with OBDwiz software. And mine shows the same Oxygen Sensor Heater test as not complete.

A strange quirk (sloppy programming) is that on the Monitor Status Report it shows "This vehicle is ready for emissions testing" but on the larger full Diagnostic Report it shows "This vehicle is not ready for emissions testing".

We have those drive-by testing boxes in Colorado too. I'll try to find one when mine is due (it's a ways off). If I have trouble with the emissions folks, I'll rewire it with TSB 25-001-07 (Google/Duck/Brave it, you'll get lots of links).

I do get the flashing engine light as described in the TSB. But, I've owned this TJ for 11 years now and it has never failed emissions. Going for my drive by tomorrow. Fingers crossed. Still don't understand how those boxes can do a test with just a drive by. Maybe I'll tailgate a Prius as I go by.

 

[Rcroane]

I assume if I pass emissions, there is really no other reason to carry out the TSB rewire? Or, will it eliminate codes like the P031 I got recently? That being said, the re-wire looks easy enough to do. Thanks.

 

[OldBuzzard]

As I understand it, the Emissions Monitors stuff has just about nothing to do with the rest of the OBD system. The monitors don't throw error codes, and vice versa. But I could be wrong. It would be interesting to get hold of the source code to an OBD computer, or at least a fairly detailed high level flow of some sort.

 

[ItchyDong]

If you have a scanner with live data and graphing capability, you can visually see the o2 heater working from a start when the engine is cold. Pull up and graph B1S1 and B2S1 sig with key on engine off. Both should read right around 5 volts (bias) when the engine is cold. Start the vehicle. A properly functioning heater will force the signal to a lower voltage. You should see both signals immediately dive. If they do, your heater circuit is good. No need for an ohm or voltage check.

 

[OldBuzzard]

Why does an oxygen sensor need a heater anyway? It seems like a sensor sitting in the hot exhaust flow is the one place that doesn't need a heater.

 

[ItchyDong]

Why does an oxygen sensor need a heater anyway? It seems like a sensor sitting in the hot exhaust flow is the one place that doesn't need a heater.

It's literally all about emissions. Imagine that? The O2 sensor has to be hot to function properly. The faster an O2 reaches operating temp, the quicker the engine goes into closed loop, and the quicker the PCM can command proper fuel trims to optimize catalytic function. *Boring*

 

[OldBuzzard]

Thanks for the explanation, that makes sense.

As much as we all hate the emission control side of PCM/ECMs, I do like the extra power from computer controlled ignition and fuel injection. This little straight six makes almost as much power as many V8s when I started driving. And I haven't had to fiddle with a carburetor with a sticky choke, or a flooded engine under a couple of feet of snow and -10°F to get a car started in several decades now.

 

[hear]

Edit: I did get 12+ V when I tested the harness side of the circuit. I'm actually going to get my emissions test tomorrow. In Virginia, we have those drive by testing boxes that sit on off ramps. I have know idea how they are able to test in a 1 second drive by, but I fully expect to pass.

I'm not sure how that works, but it's closer to making sense than what we have in Texas. They don't actually measure your emissions, they just essentially run diagnostic test to make sure the CEL isn't on and that all the sensors are working. Which means that it's not enough to have your car spitting out the proper level of emissions, you have to have all the sensors reading correctly too...so the test isn't actually about emissions its about sensors. Which is annoying because I have a friend with an XJ that appears to run fine, but the OBDII port won't communicate so it can't pass the test.

When I was a kid in IL they would just stick a sniffer on the exhaust and measure the output. That's all that really matters. Of course I'm sure we're less interested in reducing emissions than we are about making people spend more money. So in that regard the TX policy is flawless.

 

[Rcroane]

Turns out my '06 TJ doesn't qualify for the drive by method in Virginia. So, it had the full monty exam this morning (not even close to a CA exam) and passed with flying colors. The inspector told me that as long as only one monitor is showing not ready, that alone is not a reason to fail.

All set for two years now.

 

[hear]

Turns out my '06 TJ doesn't qualify for the drive by method in Virginia. So, it had the full monty exam this morning (not even close to a CA exam) and passed with flying colors. The inspector told me that as long as only one monitor is showing not ready, that alone is not a reason to fail.

All set for two years now.

Congrats! It was a real struggle to get my JKU to pass. We celebrated when it did.

in TX 97's & older are exempt (anything over 25 years is emissions exempt). 20 years & older can have 2 sensors showing not ready, newer cars can have 1 sensor not ready. But the CEL must be off. You can have stored codes, but nothing pending or active. I confirmed this by waiting for the JKU CEL to go off with all the sensors ready with a stored code. I got there as fast as I could and didn't turn the engine off while waiting for my turn.

My buddy on the other hand, he drove to a shady place in McKinney and simply paid a "$75 passing grade tax" to reach the same outcome.