I get a check engine light within seconds of start up. Had been getting P1646. Which is the RH or (passenger side in the US) upstream O2 sensor. I erased it 3 times and it came back the same way each time. Car drives fine and I don't see anything different with power or fuel mileage. If I erase the code it does not come back until the next restart. Never comes on while driving always just a few seconds after starting. Hot or cold.

Got the proper upstream Denso O2 sensor #234-9030 for $78 including shipping from 123AutoParts.com. Had not used them before but they beat Amazon and EBay by a couple of dollars.

The old and new sensor measure the same electrically. Old one looked in good shape. The new sensor gave the same P1646 error code after a start or two. Now I am getting P1647 which is the LH or drivers side upstream O2 sensor.

This is getting me confused. I have put a ScanXL fuel trim plot below. Maybe someone can see a problem? I do see side one showing some positive numbers in the 3-4% range but that seems within the normal range??




Anybody see anything??
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Any signs of an exhaust leak before the catalytic converter?

 

No the exhaust still sounds the same. I am thinking of putting the old passenger side O2 sensor in the drivers side. To see what happens??

I will say it was very easy to change any of the 4 O2 sensors in the S Type. I was very happy to see I could change them in about 10 minutes!!

One of the few things that is easy on this car!!

Anybody that does data logging see anything in my plots?
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I couldn't see anything useful in the data, not that there's much of it.

Maybe check the freeze frame to see when the codes flag, but this sounds more like a wiring/harness problem (or something else) than actual sensor fault.

If you want to look at more O2 data I suppose you could try live data and blip throttle, then check both sides are fairly alike. If they are then I can't see it's the actual sensor (unless a tech has ideas).

 

Thanks JagV8! But I posted side 1 and 2 fuel trim plots. They show a range of RPM's and load values. I generated those plots by driving around at different speeds and loads for about 30 minutes.

They seem to be slightly negative on side 2 and a bit positive on side 1. So one side is a bit lean and the other side is a bit rich?
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I don't see how that helps reveal anything, other than that they O2s aren't utterly broken all of the time.

 

Wanted to finish up the thread. I started with a P1646 code and changed the RH (passenger side in the US) upstream or wide-band O2 sensor. Still instant check engine light but now the code is P1647? Which is the drivers side?

I then swapped the old RH sensor into the LH or drivers side. All codes gone. Don't know what happened but the old driver side sensor heater circuit does measure differently. So It does have a problem. Don't know why I got the wrong bank the first time??
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Horrors, that's so confusing!

 

Gee, those maps look strangely, familiar........

What I see in those maps is proof the car really has no fueling problem. The trim cells that have populated are all within a range that are acceptable. I'd begin getting concerned if we started seeing values of 8-9% or higher. That tells us the sensor itself is functioning if it is kept warm enough by sustained driving.

So that leaves us with the sensor heaters. I think you have sort of eliminated a heater itself as a failure by your substitution and moving them around. You also need to understand that many times the "fault" seeming to move from side to side is a consequence of how the system works. Once some codes are logged, the system stops running that or other sensor tests, because it knows that if that failure has occurred, other test results are probably compromised and not reliable. In other words, if a P1646 sets, it could stop looking for the P1647; might lead you to believe the problem is on one side only, when it actually affects both sides.

Conversely, an O2 heater fault can be recorded if the power source to the heaters is compromised, say by an O2 Heater relay with burned contacts. I think the '05's have the relay in the front fuse/relay box along with a fuse for each side. Might be worth swapping a new relay in for the heater and see if the faults are gone for good. Could also be a harness wire chafed somewhere in the way down to the sensors.

Cheers,

 

Hey buddy! I thought you might know those! Sure am thankful for your custom layouts. I am still learning the ELM327 and ScanXL but they sure can do a lot.

Way beyond me but a great learning opportunity.

Yes there is a 30 Amp fuse for each O2 heater. It must run other things too because I can't believe it takes 30 A just for the heaters?

I have more driving on it and it does seem to be fixed so definitely a bad drivers side wide band O2 sensor.
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these 2 codes are only for heaters. nothing to do with air to fuel ratios. the heaters are there to get the 02's up to temp fast to reduce emissions as has been touched on. they will set right away when they go out. and occassionally they take out the fuses (and fuse box connections) but mostly only go open circuit. Think light bulb filament that heats up and glows till it pops the filament. Thats all it is(without the lighting part )
But this is a reason I no longer use non OEM 02s, Ihad issue with them. a XJ or Stype are fairly easy to change, not so with XK or X types. These are a couple things I just wont put cheapies in for if someone wants them. Make sure you have power on that circuit and of course grounds but if I remember the ground is a multi, so youde have more than those 2 issues if a bad ground

 

Glad to see they are helping someone out! ScanXL has proven to be a gem.

Nothing else on those fuses, one 30amp fuse for a pair of sensor heaters. They are important, especially during warm-up.

You keep at it, you'll learn your way around OBDII. Good luck!


Cheers,

 

Thanks Brutal. I used the OEM Denso O2 sensor. Just too cheap at $68 delivered to go with anything else. But it is a breeze to change on the S Type! I was very surprised at how easy they are to get at.

Steve;
My 2005 has a 30A fuse for each side. Or does that fuse supply both the pre and post cat O2 sensor heaters? I was not sure if the post cat O2 sensor required a heater?
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Yep, one fuse for each side, feeds both upstream and downstream heaters on that side. I think the only cars that did not have heaters on both was the AJ26 V8, '97-'99; they only had upstream heated sensors.

Cheers,

 

hey, quick bump up, i have an 03 stype 3.0 with only the p1647 code, i was going to change the upper driver o2 sensor but this post made me change my mind. where are these 02 heaters located? and how can i troubleshoot them?

 

The heaters are inside the sensors (& not changeable; you change the whole sensor).

 

gotcha, so probably a wiring issue or replacing the whole sensor will probably make the light go away. i can erase the code but the first start up will make MIL light illuminate again.

 

You could swap side to side, to see if the code moves, but beware they can be in VERY tight.

 

Gotcha, thanks!!

 

Was your P1646 and P1647 codes caused by a short in your wire harness?