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Old 10-23-2000, 09:20 PM
Ralph Burnette Ralph Burnette is offline
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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