brunnhilde limped home

Pretty woman spells trouble, many would say. A week ago Tatyana Brunnhilde went shopping for new shoes. On the way home I could tell she was not herself. Her pace was sluggish. Fortunately the trip was short and we made it home uneventfully.

The check engine light came on when we left Costco. Unfortunately I don't have a ODB reader to find out what fault codes were recorded. In desperation I start checking some items that are relative to determine if they fail or not. Reading other people diagnostic with similar symptom I check a number of things.

i removed the heat shield to check the turbo charger's servo actuator to see if it actuates by the ECU

my neighbor told me to check the manifold air temperature sensor - he said his sprinter always have problem with it when it is covered with oil; even though i was skeptical that oil would not hurt a thermistor type sensor i check and clean it; i was correct that the sensor is good (after checking the resistance at two temperature points)

 many forum member report stuck EGR valve but these are on vehicles with very high mileage

i deemed the manifold air flow (MAF) sensor is very unlikely given the low mileage; likewise the intake air pressure sensor on the air cleaner box

not being able to see the bottom linkage I could not tell if the shaft has seized as some people reported

 

figuring out how to remove the circlip on the upper linkage is tricky - i was very careful least it fly off and disappear into the abyss

 after some elbow grease i removed the servo actuator out of the vehicle

knowing there is a worm drive gear inside i just check for the gear lash to verify the shaft is not seized to the bushing

desperate for a ODB reader I spend a good part of the morning recommissioning the palm pilot ODB reader i bought 8 years ago; loading the software is the hardest part; with it i finally was able to read the DTC (diagnostic trouble code) that caused the CEL; the code is "bank 1 sensor 1 O2 sensor HV"

because my reader cannot read manufacturer specific DTC i waited a few days for an appointment with a local sprinter owner who has a reader similar to those used by the dealer service tech; while the DTC is different it is also O2 sensor voltage problem
armed with this information i now feel the likelihood of the O2 sensor at fault is high, i ordered a sensor from amazon (at 1/4 the price of the dealer)

It was a challenge to replace the O2 sensor. I struggled a long time because I could not find room to fit a wrench. Eventually I found only one spot I could fit a wrench and have may be 10 degree of rotation. With the help of a length of 2x2 wood I was able to assert enough force on the wrench to free the sensor. Putting in the new one was a snap. It came with anti-seize compound and I just lightly tighten the sensor onto the exhaust manifold.
the engine started immediately and there is no CEL; from the sound of the engine i immediately knew the ECU has de-asserted the limp home mode (LHM)
checking with the ODB reader the DTCs are gone

I went for a test drive and Tatyana Brunnhilde is back to her normal self. I am very surprised that the O2 sensor fail on such low mileage.

you can see the soot - i wonder if the soot was caused by the limp home mode when the ECU keep the air fuel mixture very rich to protect the engine from damage 

The trouble shooting would have been much faster had I have a good ODB reader capable of some dealer service DTCs and subcodes. I am going to invest on a PC based reader from autoenginuity. It cost about $500 (for the generic reader and the Mercedes Benz enhanced module) but just avoiding one trip to the dealer service it would recoup itself. I don't think I would go on a long trip without a reader.

Feeling happy the trouble is behind us, I gave Tatyana Brunnhilde a good shower. I even remove the read light assembly to clean out the moss. I have been wanting to do this a long time.
tatyana Brunnhilde's dirty butt - only the lens on the north side has moss build up

it turned out most of the moss you can see are not at or behind the gasket; it is in the seam between the clear plastic lens, and the opaque white plastic of the inner body; I use a strong jet of water to dislodge most of the moss but there is a little got driven deeper into the crevices; the lens now looks a lot better after cleaning

after cleaning

these two ugly labels also need to go

may 18 update:
While shopping for the Bosch O2 sensor the thought of buying the universal sensor crossed my mind. I am one always looking for way to save a few quid but in the end I wanted to take the safe route so I bought Bosch 17019. I saved the old one so I can reuse the connector with a cheaper universal sensor.

I want to have a spare O2 sensor as a spare so I went to Bosch's site to find it to no avail. I called their technical support and talked to an AE. It turns out Bosch only make universal sensor for narrow band. No universal for wide band computer controlled ones like the one used in the MB Sprinters. So if you think you find a cheaper universal one it is likely a wide band for another vehicle. It might work but I don't advise using it to save a few quid. The 6-wire wideband ones are tailored to automaker's requirements.

Bosch 17019 is the only correct one for T1N Sprinter - of course if you want to pay more buying from the dealer with the MB part number.