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Old 10-22-2000, 10:28 AM
Registered User
Join Date: May 1999
Location: Somers, CT
Posts: 73
The auxillary radiator fans on my 300SD
come on after the car warms up and stay
on as long as the car is running. They
shut down as soon as I turn the engine

The tempurature gauge reads a little above
80 and, in one case, last night the
outside tempurature was 58 degrees.

A review of the posting indicate that a
sensor on the engine may be the problem.
If so, where would it be and I can I
check it?

BTW, I have 149k on the car.

Ralph Burnette
1993 300SD
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Old 10-22-2000, 06:31 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Ralph, this is probably the problem with the limp mode as well.

I would have the blue sensor replaced then recheck.

Also, the auxillary fan relays have been known to stick and run a battery flat.

Have this repaired soon, it is causing stress on the charging system.

Donnie Drummonds
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Old 10-23-2000, 08:20 PM
Registered User
Join Date: May 1999
Location: Somers, CT
Posts: 73
First, thanks for the advise.

Second, I did some additional testing:

I drove it to work this morning (almost
1.5 hours) and no problem with the fans.

I drove home this evening and the fans
were blowing when I pulled into the garage.
I shut down the car which shut the fans
down and then I turned the ignition on.
The fans stayed off.

I two diagnostic procedures for the w140:

1) Read sensors:

a. set the tempurature wheels to the white
b. turn the ignition key on (don't start car)
c. press left and right auto buttons.
d. wait at least 20 seconds and then press
"REST" for at least 5 seconds.
e. A number (1) will appear in the left
window and a tempature or message in
the right window. Push the "AUTO"
button to proceed to the next reading:

1 - in cabin temperature (B10/4)
2 - outside temperature sensor (B10/5)
3 - left heater core temp. sensor (B10/2)
4 - Right heater core temp. sensor (B10/3)
5 - Evaporator temp. sensor (B10/?)
6 - ECT sensor (A/C) (B10/8) Will return
"HI" for a short or "LO" for an open.
7 - Refrig. pressure in bar
8 - blower motor voltage (8 min - 60 max)
9 - Software status
10- Left rear heater core sensor (B10/9)
11- Right rear heater core sensor(B10/10)
12- Rear evaporator temp. sensor(B10/11)
13- Software status
16- Control App. for Active Charcoal
(yes=1, no=0)

With this test, everything returned normal.

However, with this procedure, I got a E0 41
code - short in ECT:

Procedure to check for error codes in memory:

a. left temp. selector wheel to red
b. right temp. selector wheel to blue
c. turn ignition key on.
d. press "AUTO"
e. within 20 seconds, press both "REST"
and "0" (at the same time) and hold
them down for at least 2 seconds.
f. the display will show permanent DTC
codes. press "AUTO" to check next one:


E0 41

indicating a short in the ECT sensor.

So, I think that the ECT is starting to
go. Do you concur?

In any case, I am checking the pricing of
a replacement. If it is not too much, I
will just get it and replace it.

BTW, the above procedures saved me a lot
of work.

Thanks again!

Ralph Burnette
1993 300SD
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Old 10-29-2000, 12:50 PM
Registered User
Join Date: May 1999
Location: Somers, CT
Posts: 73
I think that I found it. I have two
sensors on the inlet to the thermostat.

One has a single pole and the other
has a blue top with two poles. I assume
that you mean to replace THIS one (that
is, the one with the blue top and the
two poles).

Do you suggest putting anything on the
threads when replacing it?

BTW, in the meantime, my alternator went on
while I was on the highway.


Ralph Burnette
1993 300SD
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