Cool Harness - Anybody here use one? - Page 2 - PeachParts Mercedes-Benz Forum

JimF · #16 08-11-2003, 11:40 PM

to a CH; you can't install them incorrectly.

But you could have a bad wiring harness; they do go bad. Just remove the CH and reset the codes. Wait a short time and re-read them.

Also use an ohmeter to tell if the B10/8 sensor is REALLY open; it should read around 350 ohms or so at 90C apx. If it reads open, or much higher than that, then r&r.

rrobben · #17 08-12-2003, 12:19 AM

I almost went out to the garage and removed the CH to test, but It's past midnight here and if my wife finds me out there she will confim that I am actually, indeed, crazy! I'll try that tomorrow.

BTW, I just had the wiring harness replaced about 6 weeks ago.

Glad to hear that you can't install it wrong. I would have begun to doubt what limited mechanical ability I do have if I had messed that one up!

I'll let you know about the removal test tomorrow.

Thanks once again Jim...you're a life saver!

rrobben · #18 08-15-2003, 07:39 PM

JimF,

I had the CTS tested today while I was at the inde shop and you were apparently once again correct. It read 181 ohms at 83 degrees. According to the Alldata sheet they showed me, it should be reading around 300 ohms or so at that temp. So, it looks like my CTS is just reading the temp too high.

I wonder how many other people who THINK their 140 is running hot actually just have a bad CTS???????

I just emailed Philip in the parts shop to get a price on a new one. I think I can handle that job myself!

Thanks again. You are THE MAN!

Arthur Dalton · #19 08-15-2003, 09:35 PM

< >>

You are talking a different sensor

CTS sensor has nothing to do with the gauge sensor .
And the gauge sensor specs are :
60C-110 ohm
80C-67 "
100C-38 "

rrobben · #20 08-15-2003, 10:06 PM

Thanks for setting me straight on that Arthur. I just assumed that the guage got it's info from the the CTS. Oh well, you know what they say happens when you assume....

Thanks again!

JimF · #21 08-16-2003, 12:09 PM

straight!

The CTS is the B10/8 sensor; that's what I call it; the ECT is B11/2. Check the picture on my page under MENU#18; clearly shows both sensors.

The ECT sensor (B11/2) temperature vs resistance readings are:
Temp(C)--Temp(F)-------- Ohms
20 --------- 68 ----------- 2500
30 --------- 86 ----------- 1700
40 ---------104 ----------- 1170
50 ---------122 ------------ 830
60 ---------140 ------------ 600
70 ---------158 ------------ 435
80 ---------176 ------------ 325
90 ---------194 ------------ 245
100 ------- 212 ------------ 185

The reistance of this sensor should be within +/-5%. Again this is the ECT sensor.

The CTS (B10/8) sensor's temp vs resistance characteristics are different from the B11/2 sensor. But the key values for this sensor's resistance is the resistance value at 100C, 107C and 115C.

For 100C, the resistance sb 310 ohms;
For 107C, the resistance sb 250 ohms;
For 115C, the resistance sb 200 ohms.

At these resistance settings, the fans should come on at low speed (310 ohms); second speed (250 ohms) and high speed (200 ohms).

For your '93 500SEL (W140): If your CTS sensor (B10/8) reads 183 ohms at 80C, it is BAD! Also if your ECT sensor (B11/2) reads 183 ohms at 80C, it's bad also.

This assumes it was read correctly. Hard to see why it's that low: normal failure mode for this device (varistor) is going to HIGH resistance.

rrobben · #22 08-17-2003, 11:33 PM

JimF,

Once again, you are dead on. I have the ALLDATA sheet the inde printed for me in my hand right now. It is called "Coolant Temperature Sensor: Description and Operation". Under "Purpose and Location" it reads "The coolant temperature sensor (B11/2)........" The second page of this sheet has the temp and ohm chart listing the proper readings. They are exactly as you described. If you remember the A/C TDCs I posted, I had an E0 43 - A/C system coolant temperature sensor (B10/8), open or short circuit ** error. I asked the inde to check this out. (I faxed them a copy of the TDCs, so I know they had B10/8 in black and white). What they tested was, apparently, the ECT sensor (B11/2), not the CTS (B10/8). I looked at the title of the ALLDATA sheet, saw Coolant Temperature Sensor (CTS?) and thought they had tested the right one. Sounds as if both may be bad. My gut tells me that neither of these could be very costly, so I think I should probably just replace them both and have some peice of mind.

I'm going back to the inde tomorrow afternoon to get this straight. You have been a lifesave Jim!

Hope my ignorance hasn't put anyone else on the wrong track with their problem!

JimF · #23 08-18-2003, 10:34 AM

somebody who reads those sensors that can properly operate a ohmmeter, even if you have to do it yourself. If you not able, maybe you can enlist the aid of a neighbor.

The easiest way is to start 'cold'; just watch the temp gauge and take some readings at easy points: 60, 80, 90, 100C. As you know, 90C is halfway in between the two lines that mark 80 and 100C on the temp gauge.

The most important are the readings at 80, 90 and 100C. They should be close to what the table says. If way off, then r&r the sensor (B11/2).

Do the same thing for B10/8 and watch for the readings around 100C. Remove the Cool Harness for this testing. BTW, you probably have to close the hood to try to get it to 100C.

If the SENSORS are ok, then you may need to test the car's electronics. Mercedes recommend the use a resistance substitution 'box' (rsb).

To test the AUX FANS operation: Remove the cable that connects to the B10/8 sensor and hook-up the rsb.
1) Set the resistance to 310 ohms. The fans should come on 1st stage (low).
2) Set the rsb to 250 ohms: fans should come 2nd stage.
3) Set rsb to 200 ohms; fans should be on high.

This testing can be done with discrete resistors: select/test to make sure that they MEASURE very close to the three values: 310, 250, 200 ohms. Just clip them across the B10/8 leads.

Then let us know what happens.