P0138 Code on 2007 X3 40k

So mainly due to Sandy I have not driven my X3 for a week - Long Gas Lines.

Then we had 5 inches of snow and my wife needed it.

Shortly after starting the "Service Engine Soon" came on and has remained on.

I dropped into Pep boys and they read and reset the code P0138.

Strangely immediately after the reset the bulb fail light came on and I can't see one that is out.

I have read through some forum and most say that O2 sensors are unlikely to go at 40k miles.

I have replace O2 sensors before on a Subaru and have the tool but of course I am not sure which one it is and don't want to buy and replace all of them just to find out there wasn't a problem.

Is it possible it was a one off trigger?

How many O2 sensors are there on the X3?

Is there a way to test the O2 Sensors in situ?

If all else fails anyone know of a reliable repair shop on central Long Island NY?

Or maybe I can do it myself.

Originally Posted by BigglesTAP

Strangely immediately after the reset the bulb fail light came on and I can't see one that is out.

Most likely one of the rear tail and/or brake light bulb pairs.
Difficult to diagnose by quick look while parked as when one bulb dies the other one takes over that function.
Although you will see both sides light up when the brake pedal is depressed, there will be a difference if you look carefully.
This has fooled quite a few owners on this forum.
Best to replace at least 2 bulbs anyway while you are at it - they get dimmer with age.

Is it possible it was a one off trigger? Yes. Could have been moisture in the connection to the O2 sensor, or just a random voltage drop or spike as the battery had got a bit discharged while unused for a week.

How many O2 sensors are there on the X3? 4 - 2 pre-cat and 2 post-cat.

Is there a way to test the O2 Sensors in situ? Don't know, but unlikely to be the pre-cat ones as that would most likely affect air/fuel mixture and give bad idle.

Thank you for the prompt and complete reply this is a huge help.

I have reset the P0138 and will wait and see if it reoccurs.

I will wait until dark and have a close look at the lights, but I found it very strange that came on immediately after the code reset, having said that I recall it coming on and going off a week or so ago..


While we are here what would be your choice of 4 replacement tyres? I've looked at the Michelin MXV4

Originally Posted by BigglesTAP

Strangely immediately after the reset the bulb fail light came on and I can't see one that is out.

Remember that the brake lights have a built-in back-up. If a bulb goes out, another bulb (in the hatch assembly) automatically lights up instead. Look carefully to make sure your rear lights are symmetrically on both sides.

Well even stranger the bulb light has gone out and i look carefully in the dark and nothing is out..
I did notice the bulbs in the tail gate that i can't get to light, are these the adaptive brake lights and it there a way to test those?

Oh and any advise on tyres?

Originally Posted by BigglesTAP

Well even stranger the bulb light has gone out and i look carefully in the dark and nothing is out..
I did notice the bulbs in the tail gate that i can't get to light, are these the adaptive brake lights and it there a way to test those?

Oh and any advise on tyres?

The bulbs in the tailgate are indeed the break force llights. AFIK, they only light up when the ABS system kicks in. I don't believe there is a way to test them.

I like the Pirelli Scorpion tires (original).