I'm starting a new thread on this issue because it's not the main point of my other thread:
96 E300 OM606 won't start at oper. temp. Crankcase position sensor? Fuel pump relay?

Recap: Auxilliary fans recently quit. Determined old motor was bad (no spin with 12V power applied directly). Replaced with new OEM unit. Now works with direct 12V but does not function when connected to harness, even with engine hot and AC on full blast.

Set climate control unit to test mode (key in position 2, depressed both Auto buttons 10+ seconds); no go. Pressed "Rest" button and scrolled to #20; reading is 10.0 mA, but voltmeter at fan connector reads zero. Obviously, power is not getting to the fan.

All fuses are fine (in all 3 locations). Interestingly, the fuse designation card in the engine compartment fuse box identifies fuse #20 as "Fan," with a 40A maxi fuse, but there is no fuse #20 and no 40A fuse anywhere in the box. Could there be another location for just this fuse?

Many thanks to Matt L for some valuable suggestions. I haven't yet checked the connector at the fan with a test light, though, because I can't find my 12V test light. Matt L also suggests verifying power to the N65 pulse relay in the fuse box.

Is the relay pictured below the one you're talking about, Matt? (First pic shows connector backs open to expose leads for test purposes.) If so, I've verified that it has power because I can get readings in the 13.7V range across some of the terminals with the engine running. But check out the parts in this diagram:

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=210020&M=606%2E912&GA=722%2E438722%2E600&GM=717%2E446&CT=F&cat=45P&SID=54&SGR=040&SGN=03

The part labeled 90 is the ONLY relay in my fuse box. According to this diagram, it's p/n 210 545 02 32. Mine is 210 545 04 32. (Maybe just a newer version.) I can't find the ones labeled 88 or 96 on my car.

Any way to test this relay/control unit based on resistance or operating voltage across particular terminals?

What next?

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Bad temp sender/switch?

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

That is the part. The pair of wires from your auxiliary fan end there, on one of the two-pin sockets. The one that is at an angle in the second picture (I think).

It's not a relay. Looking at the board inside, it is apparent that there is a position for a relay to send power from one of the positive leads to the auxiliary fan, but it's a black space on the board on my "04 32." Rather, there are a pair of MOSFETs (in parallel) which supply the power. Because there is no relay, there is no viable resistance test that can be performed from the outside.

Do you have power on both of the red wires on the second plug from the back? I don't recall exactly, but perhaps only one of them goes to the fan control MOSFETs. I don't know where it is fused, if at all. I suspect that it is not. There is also no fuse #20 in my '96.

Finally, a word of dis-encouragement. You can't buy a new 04-32.

You're correct, Matt. The two-pin connector is from the fan. At the fan end, the connector leads are labeled 1 and 2. Lead 1 (brown) ends at pin 11 on the pic below, lead 2 (black w/white stripe) ends at pin 10. On my car, pins 4, 6, 8, and 15 are not used.

The red power wires at pins 5 and 7 both have power coming in.

In CCU test mode (engine off) and with engine running and hot, I'm not getting any significant voltage out of pins 10 or 11. Shouldn't I be?

Have also attached pic of inside of unit. I assume the MOSFETS are the two components left of center, covered by the heat sink straps. Note the bubbling around the wire field just above them. Significance?

BTW, speedo has decided to work again, and ABS/ETS lights are off.

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If you have the fan motor unplugged, you will not see constant power to the connector under any circumstances. This is where our fan control differs greatly from older models. Full power is never applied to the fan motor until it is turning.

When the fan is demanded, the controller will send it a series of very short pulses of current, which should start turning the motor. If it does, the pulsing continues at the proper rate to turn the fan as demanded (or full power is applied if 10ma is present at the control input). If the motor does not initially start, the cycle is aborted and retried in about five seconds. You do need to connect a test lamp to look for this behavior.

You are correct on the MOSFETs. There is no significance to the "bubbling." That's just some solder.

Note the heavy rod between the two relays and the two MOSFETs. If you look at the bottom of the board (but you shouldn't - that heat sink strap is next to impossible to remove) you will see that without this rod, there is room for another relay. I suspect that it is used on 03 32 or 02 32.

Okay, I understand. So I picked up a test lamp this evening and tried it at both pins 10 and 11 using the CCU Auto test mode. Nothing. Fan motor is plugged in.

Any seconds on rrgrassi's suggestion about the temp sender? Any other sensors/input that would feed into this circuit and (if faulty) prevent the controller from activating the fan motor? I'm not looking forward to a conclusion that the controller is bad, since replacements are not readily available.

If you activated the fan test and observed 10 on the fan control current at the climate control pushbutton unit, you can eliminate sensors as a cause of the trouble.

You're saying the fan control current displayed on the CCU would not be 10 mA unless all relevant sensors are providing within-range inputs? Is it possible that all input sensors are working, but the Auto buttons on the CCU are not working properly, so the CCU is not going into test mode and turning on the aux. fan? If that's the case, maybe the N65 is not bad, it's just not getting the signal to turn on the fan. How else to test?

Did you actually replace the MOSFETs on your 04 32? I thought about trying to pop the IC board off the metal base to look at the back, but I realized I'd have a tough time getting the heat sink back in place. Do you think it's possible to use an 02 32 or 03 32 in place of an 04 32?

If the pushbutton unit shows 10ma, N65 is instructed to start the fans at full speed, whether it is because of an input or because you put it in fan test mode. So your statement in the penultimate sentence of the first paragraph is correct.

How else to test? I wish I knew. I did replace the MOSFETs in mine, but they weren't bad. Getting the heat sink in place is not hard; it's getting it out without destroying things that is nearly impossible. If you desoldered the MOSFETs and removed the board, you could get to the piece holding that clip down. It is reinserted by simply pressing down with a screwdriver until it clicks into place. If you do a search, you will probably find the post where I list the part number of those MOSFETs. They're about $5 each.

I don't think it's possible to use 02 32 or 03 32 or I suspect that the dealer would have told me that when I asked. I believe that you have to change the N10-1 SAM and add a N76 to replace that part. That's about $800.

You can try some junkyards to find the part used. Find some recylclers on ebay who specialize in MB parts and email them a photo of the part, where it is located on the car and ask them if they can supply one...chances are you'll pick one up for around $50 or so.

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Searching for the part number brings up a number of recyclers, but of course there is no way to tell if any of them are legitimate.

Even for $100, if it works, it's a lot better than the alternative.

Not sure I follow. If the engine is cold, there would be no sensor-based signal telling the aux. fan to start based on high engine temp. The only signal would be the fan test mode signal from the CCU (or whatever unit tells the N65 to turn on the fan after pressing the CCU Auto buttons).

Now, if the only way to get the 10 mA current is for the Auto buttons/CCU to work correctly, and if there's nothing in between the CCU and the N65, then I'd have to conclude the N65 is receiving the proper signal but is not activating the fan. In other words, the N65 is bad.

What do you mean about the N10-1 SAM and N76? Are you saying that combination is a substitute for the "04 32" N65?

What I mean is that the pushbutton unit N22 tells the N65 to start the fan. The sensors communicate with N22 and not with N65 directly. I suspect that you are correct. Of course, it is also possible that N22 is bad and not sending the signal. However, the fact that you also had a dead motor doesn't lead me to suspect anything but N65 as the source of the trouble. If it were mine, I'd try replacing those MOSFETs first.

I am not sure that these are the replacement parts. I inferred this from the price, and the fact that later 210 diesels use this method of running the fan. The signal to N76 comes from N10-1 rather than from N22.

is the car still not running or just the fans now?

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1999 E300 TD 190,000
1996 Passat TDI 225,000-sold
1996 E300 120,000-sold
1998 Jetta TDI 186,000 -sold
1983 Chev Suburban C20 6.2-sold

dauber - Engine starts fine since I resoldered some of the joints in the K40 relay. Now it's just the aux. fan. Don't know if the fix is permanent, since the problem was intermittent before. The strange thing is that last night, the rear view mirror lights flashed again, but the engine started anyway. Before, those lights always meant no start. Knock on wood.

nhdoc - Agreed. Unless I come up with a better solution in the next few days, a recycler for a used part is the next step.

Matt L - I didn't mention that the dead fan motor was somewhat jammed, meaning that when I tried to spin it by hand, it could be very hard to move--almost impossible--then it would break loose and spin, then jam again. If it jammed when it failed, maybe it caused a voltage spike or something that fried the MOSFETs in the N65.

What else on the car does the N65 control? And are the MOSFETs related to anything but the aux. fan? If the MOSFETs regulate anything else, and that other thing isn't working, it would help confirm a MOSFET failure.

Finally, are you saying that if I desolder the MOSFETs (or just clip the leads), I can then remove the circuit board, leaving the MOSFETs stuck in the heat sink, and then remove the heat sink without breaking the circuit board? Aren't the MOSFETs sensitive to heat, such as from a soldering gun?