I am familiar with a cycle module being located in F1 however I do not recall it being fitted or referred to as the Cycle Module’ on a 1997 or later vehicle. I thought they switched to SAM about that time.

Like you Gilly I am familiar with the module being attached to the left side frame rail since it controls the Auxiliary Fan and because of its high failure rate.

The aluminum module should be visible through the bumper, may not be accessible though. To test the signals to it, or to replace it, yes, you will need to remove some of the wheel well lining. This vehicle must be fitted with the module on the frame rail and I believe it is referred to as N65/1 or N76.

The module I refer to is actually fitted to a 129 chassis vehicle but when I check the 210 with the component ID my info shows it being fitted in this area,NOT TRUE!!

Please disregard my previous mention of it and I humbly apologize for the confusion.

I do vividly recall having to go on a roadside assistance call where a new 210 owner had his aux fan running in the garage on a cold, rainy night, no reason the aux fan should be running. It ended up being that rear fuse and relay module. MB had a bulletin out on this guys exact problem, it was caused by poor fit or sealing of the fuse box lid. A little water can get in that relay module and really screw things up. I went to his home and yanked the 40 amp maxifuse just to keep the fan from running.

Gilly

To recap... this is a 1997 E420 (210.072; M119), produced 11/97; presently @ 90K miles. Vehicle is accident-free and has had no electrical system modifications. The original complaint was elevated engine cooling temperatures, esp. with the A/C engaged. The elevated coolant temp was found to be the result of an inoperative aux. fan.


Presently, it is known that:

1. The vehicle IS equipped with pulse module N65 (210 545 03 32), which is housed in the engine compartment fuse box. This module encompasses traction systems, HCS, ATA and AAC.

2. There is NO frame rail mounted engine/climate control electric cooling fan control module on this vehicle. There is no signal pick-up and activation module (SAM) located adjacent to the ABS pump (left front).

3. The pulse module supplies current directly to the aux fan motor via a dedicated harness that connects to the module at pin group D. Harness continuity has been verified.

4. The aux fan runs when directly supplied with current.

5. Relevant fuses have been checked, cleaned and continuity confirmed.

7. Aux fan activation criteria (engine coolant temp > 95 deg C or refrigerant pressure > 14 bar) are present and have been confirmed using both an HHT and reading of actual values via A/C pushbutton control module [PBCM; N22].

8. DTC check using an HHT revealed no fault codes.

9. DTC check via the A/C PBCM revealed no fault codes.

10. Aux fan activation via the HHT was unsuccessful.

11. Reading the actual values via the A/C pushbutton control module [N22] revealed the presence of control current for the aux. fan. Control currrent could be followed from 0 to 2 mA up to 10 mA, depending on presence of activation criteria.

12. Inspection of current output at pin group D on the pulse module (group D provides current to the aux fan motor) revealed no current when activation criteria were absent. With activation criteria present, control current could be seen on the A/C pushbutton control module (e.g., 2 mA) but no voltage was found at pins D1/D2, except for a brief spike of approx 8.6 volts, after which the voltage returns to 0. This cycle repeats every 6 seconds as long as the activation criteria are present.

13. Installation of a new pulse module resulted only in the momentary activation (<1 sec) of the aux fan at low speed. No further fan activation has occurred. Both new and used modules presently provide the same pattern of results.

14. According to WIS, the aux fan motor on this specific model is supplied curent solely by the pulse module, which in turn receives its command signal from the A/C PBCM. Sensors external to the PBCM gather data regarding engine coolant temperature (ECT) and refrigerant pressure.... ECT is passed first to the CFI control module, then, via CAN, to the instrument cluster, and finally, via serial interface K1, to the PBCM. Refigerant pressure is fed directly to the PBCM.


SO....

In light of the above, it would appear that the new pulse module was either defective, failed immediately after installation, or has been damaged by the vehicle. Inspection of the original pulse module's circuit board revealed no gross defects.


Does the pushbutton control module actually make the decision that fan activation criteria have been met and thus sends control current (2 mA - 10 mA) to the pulse module?

Or does the PBCM merely pass on the ECT and refrigerant pressure data and lets the pulse module make the decision to activate the fans?

Given the above listed findings, is it safe to install yet another new pulse module or are additional diagnostics warranted to rule possible damaged by the vehicle?

If additional diagnostics are required, what should be checked?


TIA!

As I briefly mentioned a couple posts ago, it could be the fan motor itself. I am unsure what the current draw should be, but I'd at least find out if it seems too high or low. After a brief starting spike, based on the fact it runs off of the 40 amp Maxifuse, i'd suspect that when jumped to a battery it should run at around 15-20 amps. When the fan motor is jumped to battery power, is it "howling" fast, or just *kind of* fast? You seem to be a very articulate person, sorry if this is too "unscientific" for you. This does sound an awful lot like one I mentioned in a prior post. Tech "A" ordered a control unit (pulse box) for this particular car and Tech "B" installed it only to find that when the fan was tested via activations that it didn't fix the inop fan, ended up being a motor. I also recall on that job a similar "1 sec" activation of the fan (about 2 revs), then quit, so maybe the controller actively monitors the current consumption of the fan motor and will stop the attempt if the current consumption is incorrect? It was a confusing problem because like you. I also tried jumping battery voltage to the motor connector and it did run, just not as fast as a healthy motor. Fast enough to make someone not familiar with the system to not suspect the motor is about shot. If it's a good motor there is a distinctive howl to the aux fans at full battery power, sounds kind of cool.

Gilly

OK, OK, tutorial time on the fan noise:

Motor getting bad, hooked to good battery:
Blaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

GOOD motor howl:
Waaaahhhhh-ooooooooooooooooooooooooooooo!!!!

Perhaps, someone may want to run a large gauge wire directly to
the aux fan motor and measure amperage draw. I have replaced the (in-fuse box) pulse module on 97's before because of fan motors drawing excessive amperage and killing it.
Good luck
Dr.D

A recent experience with MB electronics warrants checking the "current draw" of the fan motor(s). The control unit may be programmed to cancel actvation if the current demand is too high.
Activation may cease until a repair is made to the circuit that is in question.

Hopefully the contol unit will not need to be replaced should the current draw be out of spec.

An update for those interested - both aux fan motor and pulse module were defective...

* Checked resistance of aux fan motor - > 250K ohms, with engine at operating temperature. Resistance dropped subtantially as the fan motor cooled but was still higher than that of a new motor. Did not measure amperage draw, in light of elevated resistance.

* Installed new fan motor, in conjunction with new pulse module - fan operational.

* Reinstalled old pulse module, in conjunction with new fan motor - fan non-operational. No current found at pins D1/D2 of module.


So.... the pulse module does have a feedback circuit, where it monitors aux fan draw. The brief voltage spike observed every 6 seconds during the diagnostics was the new module attempting to activate the fan... and the brief 1/2 second run of the old motor that occurred when the new module was installed was due to the pulse module doing what it was designed to do... shut down the motor due to excessive current draw.

Thanks to all for the assistance.

Here's an old thread. I noticed my M4 auxiliary fan doing something very similar to what was described with the replacement N65 pulse controller. That's within the fusebox. N65/1 up front came in MY97, I believe. Note that the 40 amp Maxi-fuse at position 20 is not present on the E300. Gas models only? I don't know which fuse protects the M4 circuit.

Turning the control current to 10 by pressing both AUTO buttons for >10 seconds as described in the diagnostics caused the fan to attemp to start about once every five to six seconds. The N65 would make no noise (it appears to control the fan using MOSFET's rather than relays), but the fan clicked about five to ten times with each start attempt. "Helping" the fan by turning it by hand right before it would attempt to start caused full-power operation to ensue and continue until the control current was turned off (by pressing both AUTO buttons >10 seconds again).

With the engine running and the vehicle stationary, the fan starts when the control current is small, perhaps less than 3. At 2 it definitely starts and runs, and at 4 or above it just clicks.

The M4 in the car is not OEM, but is an aftermarket part marketed on Ebay and uses dual fan motors. Both motors are smaller than the original one motor in the OEM M4. I'm not sure when this behavior started, as I can't see the M4 in operation while driving, but it worked the last time I idled the car while stationary.

So now some questions, and hopefully someone knows a bit more than was addressed above.

Does anyone have a schematic for N65? The part number is above.

What is the normal startup current for M4? How long is it applied by N65, and is it supposed to be pulsed while starting? Mine is getting a number of pulses.

Here's a bump, and perhaps some more information.

I still don't know what fuse protects the M4 auxiliary fan on the 96 E300. I'm sure there is one, but there's no #20 (or #19) slot in my box.

I did a few tests tonight, by pressing both AUTO buttons for >10 seconds to demand full power to M4, key in position 2 but engine not started.

If there is no load, or a very light load provided by a 4W bulb, the pulse module acts the same as when my fan is connected with the engine off. So the pulse module definitely cuts off the power if there is an open circuit or not enough load provided by the fan.

Insufficient load shouldn't be a problem, as the fan installed shows .6 ohm when stalled (but I do not know that it isn't the problem). The removed OEM fan showed 1 ohm, and while the commutator is worn, the brushes appear to have good contact (taking it apart was a real PITA, and I haven't been able to remove the pully from the back side).

There are two MOSFET's in the N65 controlling the M4, both are labelled SUP75N06, which is an N-channel 60V 75A 250W (presumably enhancement mode) transistor in a TO-220 case. The sources and drains are connected to the same lines (fan and +12V), but the gates differ. Possibly one is controlled by the N22 and the other by another input, perhaps another coolant temperature sensor, but without a schematic I have no clue.

I do know that MOSFETs can exhibit strange partial-failure modes, but I've seldom seen it. I'm not sure that I want to try to solder in a new pair, since I think that the N65 is working. But I'm not sure, especially since these transistors aren't very expensive.

Anyone play inside one of these? I assume that nobody has a schematic. Removing the board from the aluminum backplane doesn't look easy, and I didn't want to force it, or I'd draw my own. Anyone have a dead one that can be sacrificed?

But as I didn't write down the numbers on the IC chips soldered to the board, I'm not sure that I can get anywhere. I may take it back out of the car to do that. They may be standard parts, or they may not.

I'm considering putting a lamp in parallel with the M4, preferably in an unused spot on the instrument panel (I haven't yet looked for one). It would be nice to see if it were running, which would be indicated by a warm glow to a bright lamp, depending on the speed requested. If it were not running, and the N65 wasn't the fault, it would flash on very briefly, about every five to seven seconds. Enough to get my attention.

I'm still driving with a defective M4 auxiliary fan and/or N65 pulse control module. As I mentioned earlier, there are two motors in this aftermarket M4.

The right motor is hooked to the left with bullet connectors, and I unplugged it so only the left runs. N65 starts the single motor reliably, so I can assume that it thinks that too much current is running to the fan with both plugged in.

However, I did see a >.2V drop between the red supply wire and the black/white fan power input wire during full-power operation (10ma control current). This is with both fans running, so assuming a 10A draw, this would be .02 ohms which is way too large for the SUP75N06 under saturation. As there is nothing else between the power and fan leads, I now strongly suspect that one of these MOSFETS is bad. If the MOSFET has too high of a resistance, it's concievable to me that the circuitry in the N65 would think that the current draw was too high. But I still have no idea how it determines the current draw; I just know that it does.

The local dealer lists the N65 at $179, so I'm not too terribly afraid to cut mine up. I ordered some of these MOSFETS today. Hopefully early next week I'll be able to fix the N65.

Ending the saga, with a warning.

I purchased the M4 auxiliary fan that was in my car from an ebay seller, "rojoimparts." This fan assembly appears to have failed after less than a year. It runs when full power is applied, but it's not the howl that the OEM fan gives. Since I wrote the above missive, the weather has turned warmer and made me realize that something was very wrong. When coming off the highway to a stop, I realize that things warm up, but this fan was not enough to prevent the engine temperature from steadily climbing, even with the fan at full power.

So the warning, of course, is don't buy this fan assembly. In fact, I'm completely done buying any MB parts from ebay sellers.

It was a twin-motor design, apparantly like the ACM fan that Phil sells, but I very much doubt that it is the same part. For one, there are no identifying marks on this assembly. It did cost about the same as the ACM assembly that Phil carries, but it is apparantly of very low quality.

I got a new OEM fan motor (which is the left side only) from Phil. Good price on the part at about $205. There was apparantly a small mixup in the shipping, so he sent one next-day air last week. I very much appreciated that, since I could install it in my old OEM fan assembly over the weekend.

The new fan howls at full speed, and you can feel a lot of air coming through the radiator with the engine off. It does a lot better job at controlling the engine temperature with the AC running.