W124 M104 code 11: O2 sensor?

[Dave Lewis]

Hi chaps, help needed for '96 S124 E280 Estate. Symptoms: misfire on acceleration, (engine spits back then picks up), idle stumbles momentarily then recovers.
Car has new loom, new coils, new coil extenders/connectors, new water temp sensor, new air temp sensor, new Bosch Maf. I have read the codes, and on pin 8, the only stored code is 11. I cleared the code, restarted car, got code 11 again. From a PDF I have, code 11 is: "O2S 1 heater (before TWC) - Current too high/low or short circuit".
Anyone know what this refers to? Is this the O2 sensor? if so, where do I find it? It's about the only thing I haven't replaced.
Thanks!

 

[Will]

O2 sensor = lambda sensor, it's mounted on the exhaust, if that helps

Measures the O2 levels in exhaust gasses and therefore if the engine is running rich/lean - the data is fed back to the ECU so that it can control the fuelling.

Could be faulty I guess, worth checking IMHO.

Will

 

[Dave Lewis]

Thanks Will, I've found it, it's rather unhelpfully on top of the pipe just before the cat. I just need to make sure that's what the code is indicating. Is there any way of checking the sensor with a multimeter do you think?

 

[grober]

There are O2 sensors with different nos of connectors. Some have a built in heater element to permit them to function when cold. It sounds as if your system is expecting a heater element when one isn't present or faulty? http://www.picoauto.com/applications/lambda-sensor.html

http://www.lambdasensor.com/

 

[neilireland]

Yes if you put the red probe of the multi meter on the black wire of the 02 sensor and the black probe to earth.
you should be getting a switching voltage of between 0.1 and 0.9 volt.
Would help if you can get the emissions tested as it shows alot up.

 

[w124coupe]

The wiring comes through the floor to a connector - worth lifting the driver's side carpet and checking that and also gives you a way to use a standard spanner (by threading the cable through it ) instead of buying the special one.

Older cars have the sensor connector under the car (bayonet fitting that needs a turn to undo)..

The sensor can be tested on a digital voltmeter. Connect the +ve test lead to the sensor signal wire - black wire - and the -ve test lead to earth. The voltage should ocillate from roughly 0.2v to 0.8v and back every second(ish).

Heater is across the 2 white wires - if open circuit its bust!

If the voltage is stuck high then the engine is running rich for some other reason. If stuck low then faulty Lambda Sensor, air leak or running weak for some reason.

Roughly £80 or so for a new one if needed.

 

[kth286]

Yes code 11 is the heater.

Perhaps you have water under the carpet and the plug is shorted.

Current draw is from 0.6 to 3.4 amps on those heater wires.

 

[Dave Lewis]

Thanks all, I'll investigate and update.

 

[Dave Lewis]

OK I've had a go at it:
Everything dry under the carpet, looks like it was built yesterday.
Heater is open circuit.
No voltage at all from black sensor wire.
So I did a slightly cruder test: unplugged the whole thing, and ran the car. Exactly the same symptoms.
So I guess it's a new O2/Lamda sensor. What make was OEM? I don't want a cheap copy

 

[w124coupe]

Bosch. Should still have the part number etched on (under the dirt!)

 

[Dieselman]

OK I've had a go at it:
Everything dry under the carpet, looks like it was built yesterday.
Heater is open circuit.
No voltage at all from black sensor wire.
So I did a slightly cruder test: unplugged the whole thing, and ran the car. Exactly the same symptoms.
So I guess it's a new O2/Lamda sensor. What make was OEM? I don't want a cheap copy

Did you check the black wire is definitely the correct colour code. Some are black, some are grey for the signal wire, the opposite colour being the Gnd.

The heater isn't required, it's just to aid rapid warm up for quicker operation.

 

[Dave Lewis]

Did you check the black wire is definitely the correct colour code. Some are black, some are grey for the signal wire, the opposite colour being the Gnd.

The heater isn't required, it's just to aid rapid warm up for quicker operation.

The black wire is on a separate connector, joining to a thick green wire, and is a thicker guage than the other 3 wires on the other connector (two white, one brown). I'm guessing the brown is the earth, and from what's been said above, the white ones are for the heater.

 

[Dieselman]

The pair are the heater, the other two could be interchanged. Just perform a continuity check to find the Gnd wire, then meter the other one for voltage.

 

[Dave Lewis]

OK, just done a continuity check, and confirmed that the black wire is not the ground, the grey one on the same connector as the heater wires is. I metered between the black wire and earth again, still nothing at all. Meter is switched to 0-2 volts scale.
If code 11 is the heater, should I be getting code 13: O2S (Lambda) control system operating at rich or lean limit if the sensor is dead?

 

[Dieselman]

I just want to check you are running the engine when metering the black wire.?

It appears though the heater continuity is monitored, but it shouldn't be essential for operation.

 

[Dave Lewis]

Yes, engine running

 

[Dieselman]

Sounds like it's fubidoobar then..

Just one point to note. Lambda sensors don't work below 300c. Is the engine hot enough for that.?

 

[Dave Lewis]

Just what I was thinking. It's quite a long way back from the manifold, which is presumably why it needs a heater. I'll try once more tomorrow after getting it hot.

 

[Dieselman]

Connect a flylead to the signal wire and a suitable Gnd then go for a drive and read the meter from the comfort of the seat.

 

[Dave Lewis]

Good plan.