Bad Oxy sensor causes HARD shifting? - PeachParts Mercedes-Benz Forum

brookspw · #1 05-25-2006, 05:09 PM

1994 c280.

Dealer replaced the crank sensor. When I drove in it shifted fine. When I drove out it shifted hard. The shifts are so harsh you think it is going to break something.

Research said a vacuum line is probably disconnected.

Diagnosis by said dealer: It is the Oxygen sensor -- no vac lines loose.

Now, maybe I'm missing the boat here -- but:

1. How does an O2 sensor cause this?
2. How did that mysteriously start at the time of that repair?
3. By the way, the duovalve also went out about 3 days after this repair.

Something fishy here. Thoughts?

Mike Murrell · #2 05-25-2006, 07:19 PM

Someone knocked something loose while they were replacing the crank sensor.

The O2 sensor story is just more $$ for the shop.

My 2 cents.

brookspw · #3 05-26-2006, 12:39 PM

Quote:

Originally Posted by Mike Murrell

Someone knocked something loose while they were replacing the crank sensor.

The O2 sensor story is just more $$ for the shop.

My 2 cents.

They insist it is the sensor. Can this possibly be true? I see no reason that would cause a hard shift problem.

They also insist that no vacuum lines are loose.

I have to go over there shortly. Any thoughts would be appreciated.

A264172 · #4 05-26-2006, 02:12 PM

A bad 02 sensor can play havock with your mix and cause intermitant poor running and stalling, bad fuel economy... but I fail to see how it could cause 'straight up' hard shifts with no other symptoms. The O2 sensor is a primary input into the computers fuel trimming, so if the system is running well, aside from shifting, I would say they are lying...

brookspw · #5 05-26-2006, 04:08 PM

Quote:

Originally Posted by A264172

A bad 02 sensor can play havock with your mix and cause intermitant poor running and stalling, bad fuel economy... but I fail to see how it could cause 'straight up' hard shifts with no other symptoms. The O2 sensor is a primary input into the computers fuel trimming, so if the system is running well, aside from shifting, I would say they are lying...

So I pick the car up today. They replaced the duovalve and all is good with the A/C. She said they could find no vacuum issues and insisted it was the O2 sensor (no engine light, btw).

I explained how I didn't feel that could be it, that it has been fine forever and just happened to start hard shifting as I drove away from having a repair that disassembled the area containing the vacuum lines.

I'm eating lunch (15 minutes later) and she calls. Said she discussed it with her GM and they don't feel comfy with the issue. Can I bring it back in? They will keep it the next few days and give me a loaner (brand spaking new 230 Kompressor).

Gonna figure out what the harsh shift and starting problems are. Someone else was standing nearby as I explained the O2 to her. I think they must have told her that the tech may not be quite right.

A264172 · #6 05-26-2006, 04:36 PM

Good for you. Sounds like they will deal with the issue correctly this time.
And perhaps refund the O2 sensor work? Either way you can take out your frustrations on their kompressor for a few days