JettaRed

iTrader: (1)

My check engine light (CEL) came on yesterday. I scanned for codes and got P0178, stored and current. I tried clearing but the code came back immediately. The description said my fuel quality sensor (also known as a Flex Fuel Sensor) was shorting to ground.


The part number for this sensor is A 000 905 42 00.


The sensor is located on a fuel line about midway between front and rear of the car on the driver's side. You have to remove the plastic splash guard to access it.




Everything looked good and wires were intact. So, I naturally thought the sensor was bad. They are about $200. There is a short wire between the sensor and a connector passing into the cabin.


NOTE: I have posted elsewhere that I found my rear carpet soaking wet after about a week of rain and there was water puddled/pooled beneath the carpet, front and rear. (I still need to figure out how the water got in.) For kicks, I decide to disconnect the round connector to see what I could. When I did, water poured out! Here you can see a drop of water from the female part and wetness on the male part. (No juvenile remarks, please!)


I ended up cutting the carpet (which was no big deal since floor mats will cover the cut) to locate the connector inside the car. The connector is under the driver's seat, right side rail. I unbolted the seat to move it out of the way. I blew out all water from the connector with compressed air.


After that, I reconnected everything and scanned the car again for codes. No more P0178 or any code! Saved a bunch of $$$! 🤑

I should also say that any rubber plugs in the floor I have removed so that if water gets in again, it will drain out immediately and NOT accumulate. I know it may be putting out a "Vacancy" sign for mice and other critters, but I hope not. The long plastic splash guard under the floor should keep water from infiltrating into the car through the holes.

JettaRed

iTrader: (1)

It's been over six months that I fixed this code. I should check and see if there is any corrosion on the connectors. I do check the carpet for wetness after a rain and it's been dry. I used compressed air to blow out any debris from the sunroof drain channels.

dpell

@JettaRed
I wonder if there can be multiple, different descriptions associated with the P0178 error code. I also noticed that your fault code (seen on the provided image of the scanner's result screen) that yours is P017800 and not the P0178 that shows on my (cheap) scanner. The description shown on my scanner:
fuel composition sensor circuit low.

I also get a P062B

dpell

These appeared for me almost two months after water leaked into my car from clogged sunroof drains on the driver side (there was over an inch of standing water in the footwell area where your heels rest while driving). I had dried all visible water and most of the moisture you could feel on the carpets by running a variable speed space heater near the lowest heat/fan speed setting. I regret now that I did not spend the extra time removing the floorboards.. I definitely could hear swishing water underneath the carpets for a day or two after the puddle was found.

JettaRed

iTrader: (1)

There are rubber plugs in the floorboard that I removed to let any water run out immediately instead of accumulating.

My car is also configured for flex fuel. I'm not sure that code applies to cars that are not since it is ofter also referred to as the fuel quality sensor. Mine said "short to ground" and yours is saying "circuit low". I guess they mean the same thing.

I would disconnect any connectors you find and use electric contact cleaner and then compressed air to dry them out. Those cans of compressed air for cleaning keyboards and inside of computers also work well.

dpell

Thanks again for all of your helpful info @JettaRed .

So I reviewed the previous scan that the auto shop had done for me when the codes first appeared (using their obd scanner). As it turns out, my fault code is the same as yours (short circuit to ground.). So my cheap scanner gave me vague information.. I'll now revisit tackling removal of the carpeting and the driver's seat. Did you completely remove the seat from the car? If so how did you remove the seat belt? I am a little concerned about the airbags mounted on the sides of the seat.

Questions:
I wonder if everything applies to my 2013 C300 as with your model (same scenario and locations of the sensor, etc). And did your car ever go into limp mode with these notifications appearing after your check engine light appeared (presumably from the P0178 fault code)?

Please see images attached:



Also, did your Eco system switch itself off on its own after the water ingress? I normally shut this off right after starting the engine because I don't think it's worth the wear and tear on the starter everytime you come to a stop. However, some time after the water leaked in, it was as if I pushed the Eco button to off (on the console below the radio) and the green light went out (indicating that it was off). So I'm wondering if there are other shorts. Initially after the water leak my proximity sensors seemed like they were going haywire and acted sporadic but that went away the next day.

JettaRed

iTrader: (1)

The car never went into limp mode because I really didn't drive it much after the CEL came on and I scanned the car right away. I can't remember if I used my iCarsoft MB V3.0, LAUNCH Creader Elite BENZ, or Autel MaxiDAS. But all three are Mercedes specific. Generic OBD scanners are junk when it comes to Mercedes.

I only loosened the four bolts (two front and two rear) attaching the seat rails to the floor. I tilted the set forward and secured it to the steering wheel. I then used a razor blade to slice the carpet. Because the cuts in the carpet would be under the seat and not visible, I didn't care. When place back down, the cuts became invisible.


I'm not sure why your "safety features" are inoperative other than due to the water. My ECO start/stop had already been disabled by me. The Operator's Manual will state that ECO start/stop only works when certain conditions are met. There is a good chance the shorting caused by the water prevents that. Once all is dried out, you need a proper scanner to clear the codes that prevent your safety features.

dpell

The safety features that went out did so immediately one night driving back home (having already driven 20 miles out). This was the first time I had any issues including the appearance of a check engine light. I noticed it right away as the car slowed to about 25 miles an hour (the car went into limp mode) and necessitated pulling over. At that point there was a check engine light. I turned the key off and removed it for 30 minutes. I restarted the car and the disabled safety feature lights were now off but the check engine light remained lit. I was able to drive home normally on surface streets and kept the speed down to about 40 mph only. The next day those safety features disabled lights came back on so I took it to the shop (see attachment for the codes they found on their scanner). They ended up only updating the software for fuel pump control unit / fuel pump module as it was out of date and they thought the communication issues were from that.

So you didn't have to remove your front and rear carpets? (I've read so many posts, I'm not sure if your original comments on another thread had mentioned that or not). I certainly got discouraged simply trying to just remove the lower door sill plastic body piece (that covers the seam of the carpet that comes up to meet the door sill) when it wouldn't lift straight out. I ended up partially creating small fractured all along the underside of it by the time I was able to get it out.
But with the possibility of other water related electrical issues I should probably take a good look underneath both carpets. Thanks for the additional information and recommendation about fastening the seat in the forward position while working on the wiring. I did get a can of DeoxIT and will try that after using compressed air on any condensation I find. I'm praying it is a simple fix as yours was.

This picture shows the codes the shop found.

BTW - you may notice the mention of a low car battery condition on the invoice. In an effort to resolve the issues on my own, shortly thereafter I ended up replacing both the main and auxiliary batteries for my car. That had no effect however (I thought it truly was a low current condition as the obd fault reader mentioned).

JettaRed

iTrader: (1)

I don't think the software update hurt anything, but doubt it was the cause of the problem. To access the rear floorboard, I removed the back seat cushion (it lifts up, check youtube) and pulled the carpet forward. It's not easy. I found water puddled underneath the carpet. I pushed out the rubber grommets so that doesn't happen again. The under car trays keep water from splashing in.