Check Engine light when car is off?
 

Is this normal? I got into the car this morning and the check engine light was on....This is without the key in the ignition. I drove it to work and the light went off as I started the car.

...Just got home and this time the light was on all the time I was driving. The diagnostic light bleeps 5 times which I hear means the O2 sensor...(I replaced it less than 10k miles ago??)

Should the light be on all the time even when the key is off?

bad OVP. Had the same issue. There is a thread on it somewhere that I started.

Re: Check Engine light when car is off?
 

I have also had this exact problem with my W124 and I 100% agree with "amg280" that it is the OVP located to the right of your battery.

A suggestion, until you order the new OVP, you can remove the the 10A fuse from the OVP itself when you're not driving the car. This will save your battery from draining like I experienced. I was amazed at how that check engine light drained my battery overnight after a couple of nights.

Since the change, there has been no problems.

I replaced the OVP about 25k miles ago....

I just removed the negative side of the battery and plugged it back in and it seems that the check engine light is no longer lit, nor does it say I have any bad codes.

Very strange....I'll keep my eye open though in case it happens again.

replace the ovp. it will rear it's ugly head the same way you experienced or in another way. i like to replace them with oe parts every 8 years or so. cheap insurance. good luck, chuck.

Got a new OVP today...I pulled the old one out and it had actually fell to the side and had water all over it and in the fuses....This would make sense as it started raining here in california about the same time this problem started happening. Rain stopped for a few days after I reset the codes and this morning I had my car in the garage(no check engine)....but after I got into the car after work while it was raining I came back to the car and the check engine light was on. That has to be the problem.

...No point returning this new OVP though...Always nice to have a spare one in the trunk anyway.

So my question -- How is it supposed to mount exactly? I'll zip tie it for now until someone can tell me how it mounts because I don't see.

Thanks for pointing me in the right direction!

Beware!
 

Wow! My car did the same thing yesterday. I had started an thread on this back in november. I put in a brand new OVP 2 months ago for same issue. Yesterday it rained ALL day. I get to my car to go home from work, and yup, check engine light is lit. Im just like WTF.

I inspected it when I got home, and it was soaked with rain water. apparently in one of the unions of the plastic "gutters" under the windscreen, water is allowed to drip, DIRECTLY above the OVP. I have it out now on the heat register in my house and will try it in the morning. When I put it back in, im going to zip tie it deep in the back, and not in the normal mount.

W124 6-cyl owners beware. Be sure your not getting a water leak in your electrical box behind the battery.

There is supposed to be a cover behind the battery, it hooks under that drip seal you're talking about, and keeps the electricals/electronics from getting wet and from getting corrosive gasses from the battery.

There is also a drain in the bottom that commonly gets clogged with decaying leaves. If you remove the battery and vacuum the area including below the blower, your car will thank you.

My cover was in place. Thats the funny thing. I make sure everything is meticulously reassembled.

I will re-check the union...

Well there is a gutter that takes the rain water away from the K-Jet brain and fuel pump relay....But it happens to fall just to the right of the OVP....So that is how it happens. Just make sure that the seal around the hood is pushed all the way down and the plastic cover is pushed down fully.

My problem is resolved!