coolant level sensor

Clay.0 · 11-16-2003, 05:47 PM

i guess that it's a common problem for this sensor to get gummed up and fail. so i replaced the sensor and i'm still getting an message on my obc. any ideas? could my obc be bad if i'm getting all these errors? or do i just have a lot of errors?

blkongry · 11-17-2003, 08:08 AM

what do you mean "all of these errors"? Did the coolant level error go away and now you have others? Or has the coolant level error stayed even with the new sensor?

Clay.0 · 11-17-2003, 12:26 PM

by other errors i mean like the license plate failure and not being able to program the time and date. the error has stayed with the new sensor. it only comes on when i turn off the car after about a 10 minute drive. if i start the car only for a few minutes it won't come on when i turn it off

Wayne 962 · Wayne 962's Garage

Do you check the coolant to see if it's low right after the sensor comes on? It may be rising and falling...

-Wayne

Clay.0 · 11-17-2003, 06:18 PM

it's not low, would it go off if it was too high?

Larry F. · 11-17-2003, 07:58 PM

The sensor in my '95 M3 died, and I still got "coolant" messages for days after I replaced it. Resoldered the connector, checked wire bundles, wiggled everything, no help. Coolant level was very steady through all this. Here's the part I hate: it quit giving the bogus errors after a week or so. And no difficulties in the intervening several months.

Lastly, there is no way the mechanism would know if the level was too *high*.

Just my observations, Larry F.

Jared at Pelican Parts · 11-18-2003, 07:45 AM

ON my car, i started having this same problem, I simply cleaned out the connector, and cleaned the shaft of the float, problem solved.

blkongry · 11-18-2003, 09:15 AM

It's just a float switch, right? Can you take it out and physically engage/disengage it to see if is working? Or just put a continuity tester on it? Also, someone at sometime told me that BMW does a lot of redundancies on their sensors (meaning running two in parrallel, in case one fails) to ensure reliability. Is there truth to this? If so, is there a second sensor that could be fouling up the system? (perhaps they aren't in parallel... perhaps they are in series?)

Clay.0 · 11-18-2003, 12:31 PM

larry, thanks for the info, i hope that it just goes away too. when i replaced the old sensor it was really dirty so i can see why it failed maybe cleaning it would have worked. the guy i bought the sensor from said that it was the only coolant level sensor

Wayne 962 · Wayne 962's Garage

I'm not aware of any secondary coolant sensor, although it may glean this information from other sensors in the block (although I doubt it).

-Wayne

Larry F. · 11-19-2003, 06:24 PM

blkongry:

I have never run into multiple sensors looking at the same variable. I have also spend a great deal of time poring over the schematics in the Electrical Troubleshooting Manual - ETM - which I highly recommend every one of us get! Anywho, no parallel or serial connections there. Wayne points out that there are a *number* of sensors, but they are reported out differently, and are not redundant. It *is* just a float switch, a magnet moving near a reed switch, so you can flip it back and forth. If you have dealt with the fact that the sensor is at the *bottom* of your reserviour!

Jared:

The form factor of the switch on your E30 is different, and much easier to get to - being "above the high water mark", if you will.

Glad the cleaning worked for you. Those switches also tend to leak - coolant gets into the shaft with the reed switch and dissolves the tiny circuit board and solder connections. I have been successful pulling the switch apart and resoldering the connections, resealing the part behind me, but I don't like to leave that kind of fix in the car. I imagine you get a pretty good price on that part!

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by Larry F.
blkongry:

I have never run into multiple sensors looking at the same variable.

Okay, why does the E36 have two fuel tank sending units? One is built into the pump, and one is a separate unit?

-Wayne

Larry F. · 11-19-2003, 09:17 PM

Ya caught me out, Wayne! .

Yep, two fuel level sensors (dragging open my trusty Electrical Troubleshooting Manual) wired in series yet. Soooooo, just to split hairs, they *are* measuring two different variables: the fuel level in the two compartments of the tanks.

But your point is made: never say "never"!

Larry F.

Wayne 962 · Wayne 962's Garage

That makes no sense - how can the tank have two separate compartments with different levels in each if the fuel pump is located only on one side. It's not a Jag...

This fuel sensor thing has been bothering me for several weeks now. I guess since it's in series (I checked my book too!) then it can't be for redundancy. If one unit fails, then the circuit fails.

There must be a logical reason for this...

-Wayne

Larry F. · 11-20-2003, 02:01 PM

Wayne:

The plastic fuel tank in these beasties is described as "two-lobed" in Bentley. It looks kind of saddle-bag shaped - two compartments connected across the top. Each fuel level sender drops into it's own "bag", if you will. There is a weird siphon arrangement to get fuel from the lower regions of the driver's side to the passenger side, which has the fuel pump dangling in it. For the life of me, I don't understand the dynamics that drive that siphon.

And, reading other BB's (unfaithful me!)

there are a host of weird furl tank symptoms that could relate to the two-lobed design - guage reading empty when the tank will not take any new fuel, guage that read at one level, then over time (I am imagining the siphon slowly working) come to yet another level. The "cures" that I have read have all been circumstantial - turn the car off for a while, dance on one foot, part your hair on the other side. I have yet to run into a good discussion of the siphon and it's operation.

So it seems to make sense that the two-lobed tank would have two sensors, and add the output of the two (by putting them in series) for a single fuel level reading. Back to earlier in the thread, the two sensors *are* measuring two variables, the level in each lobe.

94-325i · 11-21-2003, 07:37 AM

I'm not sure why but alots of M3 people upgrade 2 fuel pumps when they do track.

Wayne 962 · Wayne 962's Garage

Moved to this new topic:

Why Two Fuel Tank Senders...

The tank is lobed over the driveshaft, potentially creating low spots...

-Wayne

Jared at Pelican Parts · 11-21-2003, 01:29 PM

Quote:

Originally posted by Larry F.
Wayne:

So it seems to make sense that the two-lobed tank would have two sensors, and add the output of the two (by putting them in series) for a single fuel level reading. Back to earlier in the thread, the two sensors *are* measuring two variables, the level in each lobe.

Makes sense to me. I know that my car doesnt have two senders and occasionally under hard cornering, especially if the tank is low, the fuel warning light will come on briefly until i come out of the turn. Seems like two senders wired together would solve this.

himes · 11-22-2003, 07:08 PM

Is it possible that the two tanks have any sort of mechanism that would effectively supply a tank-bottom crossfeed connection? This would keep the fuel levels equal in both lobes.

Larry F. · 11-22-2003, 09:41 PM

himes:

The "siphon" is what connects the two sides - I just don't know what the mechanism is that initiates and sustains the siphon. There is nothing (that I know of) that connects the tops.

Larry F.