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Discussion Starter · #1 ·
On the B5.5 ATQ, what triggers the 'additional' water pump? (078 121 601 B). The computer, sure, but is it the temp switch on the lower rad hose? Does it depend on that signal?
 

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That's a good question, as it only runs after the engine is shut off. At least that's the way I understand it to work.
 

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It's an after-run coolant pump only. It is controlled exclusively by the J293 Coolant Fan Control Module, not the ECM.

The after-run coolant pump runs for 10-12 minutes after the ignition is switched off, starting about 15 seconds after ignition switch-off. See Bentley p. D 19-4.

The Coolant Fan Control Module detects ignition switch off when it loses +12V on pin T6p/1, which comes from the 5A fuse fed from the "generator" "C." See Bentley schematic 56/5. The 40A fuse is always hot, so that's where the power is from.

The fuses are on the 8-position relay panel, not the main fuse box, ref. Bentley p. W97-2, bottom.
 

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Discussion Starter · #4 ·
It's an after-run coolant pump only. It is controlled exclusively by the J293 Coolant Fan Control Module, not the ECM.

The after-run coolant pump runs for 10-12 minutes after the ignition is switched off, starting about 15 seconds after ignition switch-off. See Bentley p. D 19-4.

The Coolant Fan Control Module detects ignition switch off when it loses +12V on pin T6p/1, which comes from the 5A fuse fed from the "generator" "C." See Bentley schematic 56/5. The 40A fuse is always hot, so that's where the power is from.

The fuses are on the 8-position relay panel, not the main fuse box, ref. Bentley p. W97-2, bottom.
Wow wow wow! So much awesome information! Thanks
 

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interesting topic, for reference why doesn't VW use these on the 1.8s as well, my 1.8 after rolling home seems hot due to turbo, I mean temp/thermo is at 190f, but I open the hood weather permitting to cool the ol' girl off, it's like an oven. Seems like it would only help the turbo since it is balls hot and does have water cooling passing thru it.
 

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interesting topic, for reference why doesn't VW use these on the 1.8s as well, my 1.8 after rolling home seems hot due to turbo, I mean temp/thermo is at 190f, but I open the hood weather permitting to cool the ol' girl off, it's like an oven. Seems like it would only help the turbo since it is balls hot and does have water cooling passing thru it.
That would seem to be a good idea, it might prevent some of coking in the oil.
 

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Discussion Starter · #9 ·
Ok, I got a new Spectra Premium aux fan - the old one was toast. The Spectra ran great when hooked up to the battery, but after installing it, the fan blades are rubbing against the rad support (??) or rubbing against something - it would turn by hand, but if the fan motor were to run it, the motor might burn out in a couple of months from the extra friction. What can I do? Should I move the old fan blades on the new one? Or perhaps move the whole motor to the old frame? Or can I sand down the rad support where the new fan sits in? Ideas?
 

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Discussion Starter · #10 ·
That module is under the driver's side frame horn, just behind the bumper.
I wondered what that was
 

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interesting topic, for reference why doesn't VW use these on the 1.8s as well, my 1.8 after rolling home seems hot due to turbo, I mean temp/thermo is at 190f, but I open the hood weather permitting to cool the ol' girl off, it's like an oven. Seems like it would only help the turbo since it is balls hot and does have water cooling passing thru it.
I initially left the V6 module in my car as I thought it could be programmed to work that way. The problem was that it would not run the electric fan and the a/c kept running warm because of it. I didn't want to pull the dash wiring out and waited until I thought about selling the car before swapping it to the correct wiring and module. Not an easy job. I still think it could be done, right on the turbo supply line, but I never really tried to figure out the wiring.
 
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Discussion Starter · #12 · (Edited)
nudge...


The fan control module is 8D0-959-501-C and dealers want $316.00.. I’ll look on eBay ..


Ok, I got a new Spectra Premium aux fan - the old one was toast. The Spectra ran great when hooked up to the battery, but after installing it, the fan blades are rubbing against the rad support (??) or rubbing against something - it would turn by hand, but if the fan motor were to run it, the motor might burn out in a couple of months from the extra friction. What can I do? Should I move the old fan blades on the new one? Or perhaps move the whole motor to the old frame? Or can I sand down the rad support where the new fan sits in?

Ideas?
 

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Discussion Starter · #14 ·
I'd try to add some spacers rather than modify the housing, much easier usually.
Well perhaps I can add the spacers to the motor mount on the frame of the fan, but the frame of the fan ‘slots’ into the rad support in three places and then you twist the whole frame of the fan housing to line up a single screw hole on the frame and rad support - there’s no bolts to hold the fan frame to the rad support so there’s no opportunity to put spacers there. I’ll add a picture tomorrow. I think I’ll measure how deep the Spectra fan sits into the fan frame v. The OEM fan in its original frame to compare... it’s just a bit off - like a millimeter or two.

Oh, and I think I need a new fan controller- I think I heard the 40 amp fuse pop. It sounded like a rock hitting the windshield at speed
 

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I can check the number on my old fan control module to see if it's the same as the B5.5. I think I know where it is and can actually get to it easily.
 

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Discussion Starter · #16 ·
Ok, I thought the fan wouldn’t work at all without an operable fan controller. When the A/C runs, the fan does also run - it was about at half speed ( yay, so nice to see it work!!) when the car is running and the A/C was on just to de-fog the windows. So what’s controlling it? Oh, and oddly enough, I did not hear any ‘rubbing’ sound (???) again, yay, but aim mostly confused now haha
 

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As the fan is running, the fan controller is working.
The 40A fuse supplies power for the after run coolant pump.
 

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Discussion Starter · #18 · (Edited)
Well, then is it the 40 amp that also allows the fan to run in ‘after-run’ mode? Why wouldn’t the fan keep running after the car stops? Not hot enough? Or will it only run when the electric water pump runs once the car is off?
 

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Not sure of the exact operation, but the 40A fuse would supply power for the fan in after-run mode if temps are high enough.
 

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Discussion Starter · #20 ·
Not sure of the exact operation, but the 40A fuse would supply power for the fan in after-run mode if temps are high enough.
:unsure: But it runs from something else when the A/C is on? I'm thinking more that since the fan does run from the A/C being on, it's on a separate circuit, but it's not getting a 'run' signal from the fan controller when the electric pump isn't reporting that it's in operation?
 
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