P1646 check engine light on my 2006 XK8. Reset - came back. Vehicle runs fine.

Others focusing on O2 sensor? Fuses fine in bulkhead extension, passenger side:
#1 O2 sensor heaters bank 2 upstream & downstream
#11 O2 sensor heaters bank 1 upstream & downstream
#14 O2 sensor heaters relay, EGR valve, EVAP valve, AC compressor...

After research, thinking upper O2 sensor needs to be replaced? But seeing various opinions & not 100% sure? I can reach the sensor, but the wiring tucks in under stuff & I'm not sure where it connects?

I want to be sure before I proceed. I'm seeing posts that are very vehicle specific, but have not found my 2006 XK8 & P1646 code specifically. Am I on the right track? Is that what you recommend that I do next, or are there other steps I should try first?

 

I would always follow the sequence precisely as you have done.

1. read the code(s)
2. list the code(s)
3. clear the code(s)

If the code(s) DON'T re-appear, it was just an out-of-range event. If the code(s) DO re-appear, there is a genuine fault.

In the case of your P1646, the possible causes are:

1. HO2 Sensor 1/1 heater failure
2. HO2 Sensor 1/1 sensing circuit: short circuit to ground, short circuit to high voltage or open circuit, high resistance
3. ECM Failure

Possibility (3) is extremely rare so you are left with a failed sensor (1) or harness (2) fault. Before assuming component failure, I'd investigate and eliminate (2).

I like to combine logical troubleshooting with avoiding unneccessary expenditure.

Graham

 

It connects either on the firewall near the midline (several of my cars), or swinging in the breeze near the firewall, (one of my cars where previous owners didn't put them back properly). You can follow the wires up the harness to find the connectors. Swap bank 1 and bank 2 connectors, see if P1647 appears and P1646 goes away, eliminating the harness from the bank 1 side.

If that happens, you can either check to see if the wires from the sensor are fragged, or in the more likely event, you need a new one. Then you can thank minor fortune it's vaguely easier to replace than the other side.

Just did this, with the loaner tools from your nearby auto store, it is pretty straightforward. I did need my 18" breaker bar to free it initially. Once it was replaced, it was fairly easy to get the torque wrench back in there and torque it up in a couple of steps repositioning the auto store's tool.

 

Thank you Graham & Dale. I will check the ground (if I can find it) tomorrow & report back. I'm thinking that it's very likely I need to replace my upper O2 sensor.

 

It's the upstream O2 sensor (the one closest to the engine) that I've been trying to access. I hope that it's the correct one, for a P1646 code?

I can see where the O2 sensor bolts in, but I'm only able to reach in a little ways, feeling to where the wiring harness goes? Not to mention, I can't see where a ground wire for this part might connect?

 

Remove the intake duct, it will give you more visibility/access if you don't have sufficient room to play with the connectors. You should be able to follow the wire from the sensor with your hand (upper right side close to the engine, as you note) to the connector and allow you more room to change the sensor.

 

Perfect - thank you for clarifying! Since Autozone sells actual Denso brand sensors, I think I'll proceed by ordering a upstream sensor from them. When the part comes in I'll also borrow one of their loaner oxygen sensor sockets. I'll report back here to the forum once I'm done. In the meantime, thank you all for your help.

 

Fixed. It was indeed the upstream (closest to engine), passenger side O2 sensor. After the repair I cleared the code & it didn't come back.

Warning - if you have the same problem & order the Denso "exact fit", Item #234-9125 from AutoZone:

First, they ship from California & if you're on the East Coast like me & don't pay for faster shipping, it takes a week to get it (FedEx Ground).

Second, the hole pattern in the actual sensor is different. I'm not sure this matters? Maybe it's better, maybe it's worse, maybe it doesn't matter? I attached a picture of the two of them, side-by-side.

Third, although the wire connector is identical, the entire wiring harness itself is considerably shorter than the original. Although it reaches to plug in, I was unable to keep the wiring harness from touching the rubber coolant hose, which I tested & it does get pretty hot. So in the end I spliced the new part & extended the harness by using the wire from the old harness. Just took some time, connectors, patience, & electrical tape. Otherwise, no big deal.


Original passenger O2 upstream sensor, as compared to the new AutoZone Denso Item# 234-9125

Thank's to everyone above for all your help with regard to the repair. I really appreciate it!

 

That's great Peter.

As far as the splice for anyone else who needs one, the Bosch one is the same length as the old one (e.g.

 

Great news and what a struggle, sorry for that.
In the future, please use heat shrink and not tape. Under the hood with all the heat, I use as small opening as I can on the first cover and a larger one to cover that one and pinch the ends after heating.
On double wire replacement, use one for each side and a larger one over the pair. Just good insurance.

 

Denso sell ones with a longer wire. The numbers keep changing so I'm not sure exactly which but maybe one of 234-0916, 234-9030, 234-9029

 

Nice to know Dale, for when another might stop working, thanks! I noticed the Bosch option, it was less expensive too. Although I like Bosch in general, I was nervous to use anything but Denso since there are other threads where other brands didn't solve the problem.

Thanks Wayne, I actually did use connectors. After that I covered each one with lots of electrical tape, then electrical tape around the group, just to be sure. Certainly looks like a hack job as compared to a real mechanic, but odds are the car will die while in my ownership. Spotless on top, lots of corrosion underneath, despite living in Virginia.

In hindsight, since JagV8 says there is a Denso replacement that is long enough, it seems that I should have researched it beyond AutoZone.

For now my check engine light is off & that brings me great joy.

Thanks again everyone!