Engine light on. Codes 2c9c and 2c61
 

2008 X5 4.8 with 70 k miles. Reset the codes but engine light back on. North codes appear to have something to do with "lambda probe front catalyst". Has anyone dealt with these codes? Should I replace the pre cat O2 sensors and go from there?

Sorry, missed this...


You have two simultaneous codes, one for each O2 sensor?

It is unusual for two parts to fail simultaneously... two possiblke causes:

1. A wire got damaged underneath;
2. the fuse to the sensors is damaged.

If you are gettig a "pre-heat circuit" failure, then this is NOT related to their 'function'...when the car starts up, immediately power is delivered to the sensors to warm them up- this is different that the sensing function (this is why there are 4 wires to each). Look at the wiring diagram, see of there is a common fuse (on other BMWs there IS and it is NOT in the fuse box (!!!!)). Or look at the common connector underneath for damage.

GL

A

I looked at the connector box and replugged the passenger side front sensor in. Everything looked fine. Cleared the codes but they came back a few miles later. I think both codes are for bank one, pre-cat sensor. I think I'm going to try to replace that sensor. Looks like it will be a pain to get access to it. Can't get to it from above like most pre-cat sensors, but it's also hard to reach from below, even with all the covers removed.

Have you replaced the battery, yet?
Lots of weirdness from an old battery... Just replaced mine last fall.

Battery and alternator were replaced about a month ago. Battery seems strong. Don't think that's an issue and the code stamps show 14 volts at the time the faults triggered.

Ard, would you happen to know where the fuse(s) to the O2 sensors are on the X5 4.8? I know that on some other BMWs they are under a cover in the engine compartment with the DME. Before contorting myself to replace the pre-cat sensor, I want to take a look at the fuse. All the wiring I can follow seems intact.

BTW, the actual codes are for Lambda probe heater front catalyst, control and Lambda probe front catalyst, electrical error.

I do not. Saw your other post.

Do you have access to the schematic? It should tell you the fuse, and location

The WDS shows it with the fuses under the glovebox, but it's not very clear. I checked all of the fuses there, and they were fine. I'm going to go ahead and swap the sensor today.

Wait- there should be a power and ground to the sensor that powers the heater circuit- and a separate pair for the sensor itself. (4 wires) You should figure out which two are the heater, and pop a voltmeter onto the connector to see if it is being powered- if not, then you know the sensor wont fix it.

Then again, a new O2 sensor is always nice to have!

GL
A

Ok, so I replaced the pre-cat sensor on bank 1 (passenger side) and drove around fifty miles yesterday without the engine light coming back on. I'll update after some more miles. The sensor wiring looked intact under the sheath so I guess it might have been a short or interruption inside the sensor itself.

As for replacing the sensor, what a pain! Definitely a two person job. I had to attach my crowsfoot sensor socket with two universal attachments and several extensions all duct taped together. I then pulled the sensor cable ( it's around three ft long) up near the passenger side firewall so I could feed the crowfoot down from above. I found it helpful to tape the slit on the crowfoot tool closed so it wouldn't fall out on the way down. Then I slid it down the cable as someone below the car helped it into place and held it while the other person loosened the sensor with a breaker bar. Once it was loose, I was able to spin it of with two fingers from below and the new one went in fairly easily. Now I know why the dealers charge big bucks for that job! Whose idea was it to put those pre-cat sensors there?

Edit: Been a couple of days and a 100+ miles and no engine light!!!!