Thank you very much.

 

I have a 2004 W163 ML500 with a similar problem. The fan no longer runs and I start to overheat in traffic, moving slowly.

I have verified the relay works, that I get voltage from the battery at the fan control module, and that I get +V on the blue wire. When the motor starts to overheat, using my trusty Harbor Freight DVM, I see the AC voltage on the white wire change from around 0.9VAC to around 1.9VAC when the motor gets around 90C on the gauge. I don't let it get hotter than that. My charging voltage seems fine, around 14.6VDC.

I don't know what to expect to see with a meter on the PWM white wire, so I'm wondering that whatever duty cycle it runs, seeing a cold/hot change indicates the ECM is changing the pulse width. Hard to know what to expect, but question 1 is does this sound reasonable?

Question 2 is is there some way to check the fan control module? For example, could I hook up the white wire pin through say a 10K resistor to +V and see some output somewhere?

In order to save some cost, I'd like to determine if it's the ECM, Fan Control module, or the fan. The fan spins freely and easily when I push it. And by the way I haven't found where the fan connects to the Fan Control Module yet. Pretty poor mechanic, huh?

 

Have you checked the fuse on the battery + terminal?
By the way your alternator is overcharging. 14,6 is high

 

As Art said, check the 100 amp fuse on the battery.

Also, key on and check fuses 11, 16 & 26.

 

Thanks for the input. My understanding is that the fuse on the battery is a 100 amp fuse, and if that goes, there is most certainly something wrong in the fan control module. In my case, I get voltage at the red wire on the FCM stud and using my ohm meter it seems that red wire comes directly from the battery + terminal. Because of its construction, the fuse is difficult to probe. Being stoopid which you can tell by my name, I can't figure out how to directly access the fuse. But the +V on the fan controller red wire stud should indicate I'm getting voltage there.

Thanks for the input on the alternator voltage. I will change out my alternator. Will order one tonite. I certainly don't want to fry my ECM or dashboard module. PickNPull says my van is only worth $99.

I decided to order another fan assembly with fan controller module. I'm sure it's the wrong one, although Amazon says it fits, and a comment says that it fits some guy's ML 500. We'll see. It's pretty easy to return stuff through Amazon.

Anyway, I want to thank you guys for your efforts to help out us poor Benz owners. If I were rich, I'd just take it to the dealer and let him change the fan assembly ($1100 + labor) and let them diagnose what else is broken. I had it there recently for another repair, and they never told me that my alternator was overcharging. I guess they wouldn't because when the overvoltage fries some other components, they get more work. Sigh. I took my wife's CLK 550 to the dealer (at her request (no...I mean her direction) ) to fix her TPMS sensors, and it took me $1800 to get it back after 3 return tries. Double sigh.

There oughtta be a law. I guess instead of laws against service providers screwing customers, we need laws preventing homeowner from using chemicals to kill moles in their yards. Seems appropriate. I guess.

PS my wife is rich. I'm not.

 

The price for the fan ,163 500 03 93, at the dealer is $910 dollars plus tax is $175 cheaper than Amazon.

The Voltage Reg. for the alternator, 003 154 24 06, is $86 at the dealer,

 

Major: Thanks for checking the prices for me. You're really a great participator in this website.

I'm guessing you are checking a NY MB dealer, or you are one, maybe.

At MB of Pleasanton, 1-844-426-7075, the phone quote was $1100.00 plus 9.8% tax.

At Amazon, for an aftermarket unit (which probably is the wrong one because the description says "dual", but the picture clearly is a "single" and Amazon says it fits my car...time will tell)

$375 + tax

(It's not a great idea to click a link posted on a forum, if you want to, you can find it by searching Amazon.com for a "fan 1635000393".)

There are other cheaper links, most of them are for a "293", not a "393". The 293 seems to be for the more powerful motor, ML55. It may also be a fitment issue, not sure.

Being on Social Security, and having to pay the 20% extra cost for spare parts seemingly required in California, means I need to look for bargains. I put a new aftermarket radiator in (hard job, that) and it's been working fine for 7 years. Saved a ton of $$$. The old one, right side plastic collector, blew wide open. It had OEM markings. So I remain unconvinced that aftermarket is lower quality than OEM.

Will post back as I progress on the swap out.

 

The fan assembly arrived on Friday. I removed the lower pan under the radiator, drained the coolant, disconnected the lower hose, removed the old one, put the new one in, refilled the coolant, connected the Red, Black wires on the studs and found the control plug had some interference and wouldn't plug in. I guess there are 2 different styles of plug. So I clipped off a piece of the connector that has the wires going to it, and after that, the plug would plug in and latch.

Works fine.

Saved 700 parts cost and 900 installation cost. Now we will see how long the aftermarket fan runs.

 

Oh, forgot to say: as I was checking the 100A fuse, I took off the red plastic nut and noticed it had been damaged. Since no one worked on the fan before me, I'm sure the damage was done at the factory. I was able to remove the damaged area of the shoulder on that nut, and re-assembled it carefully making sure what remained on the shoulder went down between the post and the lug. It's working fine. I will probably buy a new nut just to be safe. They can't be more than 40 or 50. For a plastic nut.

Sigh.

 

Please UPDATE YOUR PROFILE in USER CP to include the year.

 

Having a similar issue and I'm trying to determine that the plug at least has the correct voltage. So, for 12v I would attached red and brown to a multimeter and wait to the temp to get above 85 or so and should see 12v on my screen? To see if the the ECM is send the correct signal, I'd use the brown for ground and the white to positive and watch the voltage go up? What would I see with brow for ground and positive on the blue wire?

 

[QUOTE=Sebmel123;7536887]Having a similar issue and I'm trying to determine that the plug at least has the correct voltage. So, for 12v I would attached red and brown to a multimeter and wait to the temp to get above 85 or so and should see 12v on my screen? To see if the the ECM is send the correct signal, I'd use the brown for ground and the white to positive and watch the voltage go up? What would I see with brow for ground and positive on the blue wire? Just trying to eliminate the plug itself as the issue...I'm sure it is the control unit on the fan and the not the fan motor or ECM.

 

I have a issue with my 2002 ml500. She overheats when sitting. I tracked it down to the fan. It doesn’t turn on when it should. Checked both fuses. Both good. Have power at large red wire and good ground on other. Here’s where things get weird. With a ice pic type w/light bulb power checker I Check the small white wire from the ecm. And the fan runs instantly on high. Take the power pic off and fan slows to low. Turn car off then back on and no fan. Also with pic power checker on the white wire and fan roaring away bulb on checker doesn’t light.