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Old 08-05-2011, 03:49 AM   #1
kaamacat
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Default Testing dual radiator fan speeds?

Question. I am wanting to see if my fan will run both the high and low speeds with a manual override. (Checking to see if the fan is operating properly, as I've never heard it run accept when the A/C is on, which I know the HS side will kick on immediatly, and does just fine)

Car year is 1997 318ti/M44 (1/1997 build)

I've disconnected the radiator sensor plug, and can bridge the brown -> Black and get the high-speed setting to kick-in, but, when bridging the other side of the plug to brown.......I get nothing on the low-speed side. (Think it was the green stripe side)

I did this with ignition key on (engine off).

I've also seen a post mentioning that the high-speed relay (magenta in color) if bad could also cause this, where the HS side works but LS does not.

Long-story-short, how can I manually test the low speed fan?
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Old 08-05-2011, 04:17 AM   #2
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This is a fairly common issue with these cars. The fan will work in high speed mode when the A/C is turned on, but low speed never kicks on. I've heard of people jumpering it and getting low speed to kick on, but that's only while testing it. Up until a few weeks ago, nobody had a remedy except for hard wiring it to a switch and manually turning it on from inside the car. Then someone figured out a way to bypass the ecu and it functioned normally. Then... member "Noneone2" figured the whole thing out! It's the high speed relay. I know, why would the high speed relay be bad if the fan operates in high speed and not low speed? Because a faulty high speed relay leaves a circuit open on the low speed side that prevents it from operating in low speed mode. Here's his explanation:
Quote:
Originally Posted by Noneone2
CJ, Just an update on the low speed fan issue. Reader's Digest version; the high speed relay was the culprit.
After studying the wiring schematics, in the Bentley, it shows the if the high spd. relay doesn't function properly it leaves the circuit open to the low speed side.
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Old 08-05-2011, 01:14 PM   #3
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Quote:
Originally Posted by kaamacat View Post
Question. I am wanting to see if my fan will run both the high and low speeds with a manual override. (Checking to see if the fan is operating properly, as I've never heard it run accept when the A/C is on, which I know the HS side will kick on immediatly, and does just fine)

Car year is 1997 318ti/M44 (1/1997 build)

I've disconnected the radiator sensor plug, and can bridge the brown -> Black and get the high-speed setting to kick-in, but, when bridging the other side of the plug to brown.......I get nothing on the low-speed side. (Think it was the green stripe side)

I did this with ignition key on (engine off).

I've also seen a post mentioning that the high-speed relay (magenta in color) if bad could also cause this, where the HS side works but LS does not.

Long-story-short, how can I manually test the low speed fan?
Jess is correct. The HS relay contact is interlocked with the LS relay.
Additionally, the LS relay coil is interlocked with the ECU and the low temp contact in the radiator temp switch. This is the reason why the fan did not run when you bridged the other side of plug to the brown (ground). The ecu input is open. The LS relay coil has to be energized thru the ecu and the radiator temp switch contact. Here is the schematics. Follow the blue line for energizing the LS (low speed) relay coil. The ecu role is circled in blue. On early models, the ecu has no role in the aux fan operation
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Last edited by bazar01; 07-10-2017 at 02:44 PM.
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Old 08-05-2011, 01:54 PM   #4
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Thanks for the feedback...... Yesterday I did pull the HS relay (magenta in color?) and pulled the cover off. The internals seemed as-new, although I guess something could be amiss there (the diode) and I'd not know.

Now that its hot out (and I've got the head back on the car), just realized after owing the Ti for a few months the only time we'd hear the fan is when the A/C was running. Watched the car idle until temp was mid-way and no fan and the temp creeped up a tad more so I turned it off. (considering the A/C turned on adds heat to the radiator and its just not going to expend the heat in 1minute)...........

I'm gonna run to BMW today and pick up a HS relay and a new temp switch.
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Old 08-05-2011, 02:02 PM   #5
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I never sat down and actually studied the schematic. All credit should go to Russ(Noneone2) and Bazar01 for taking the time to figure this out. Hats off to you guys! Bazar01, the schematic really gives a good visual understanding of how the circuits function. I think the reason it's confusing to people is because if the fan only works in high speed mode, one would think the high speed relay is functioning properly and since it doesn't operate in normal speed mode, the normal speed relay must be the culprit when in fact it's exactly the opposite. Replace the HIGH speed relay and it should fix the problem and allow the fan to work in normal mode again. Of course this probably only covers MOST cases. There's still a very slim possibilty that a faulty temp switch, pressure switch, fuse or fan motor may be the culprit, but I think it's safe to say that if your fan comes on when you turn the A/C on, but doesn't kick on when the engine idles for extended periods, you should probably replace the high speed relay first.
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Old 08-05-2011, 02:43 PM   #6
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Thanks to all.....I'll update the posting after I pick up the relay and switch today.

(I'll have to post-up a nice fix I did for the glovebox, when the lower-left plastic stub was snapped off....vs.... buying a new part)
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Old 08-05-2011, 03:18 PM   #7
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Good stuff guys! Does anyone know the parameters for the fan to run in LOW? I'd assume a fully warmed engine, in the summer, sitting still at idle would turn it on?

Anyway, I don't ever recall seeing my fan run when the A/C was not on.
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Old 08-05-2011, 04:10 PM   #8
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I guess depending on if/how the ECU comes into play, the radiator switch is set for 80C/176f LOW, then 88c/190F HIGH..............

(On a side-note, its purely amazing at how often the words "we will have to order" come from my local BMW dealer. I found a thermostat...Stant...at AdvanceAuto, they will also order me a 2Speed switch to be here tomorrow, and the HighSpeed relay the dealer had to get from another in the area)

Last edited by kaamacat; 08-05-2011 at 04:13 PM.
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Old 08-05-2011, 04:34 PM   #9
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Quote:
Originally Posted by CirrusSR22 View Post
Good stuff guys! Does anyone know the parameters for the fan to run in LOW? I'd assume a fully warmed engine, in the summer, sitting still at idle would turn it on?

Anyway, I don't ever recall seeing my fan run when the A/C was not on.
Engine fully warmed up, temp gauge sitting at 12 o'clock, idling in traffic or in the driveway with the hood open, you can hear\see it.

If the fan don't run in low speed, there are 3 possibilities.
1. High speed relay normally closed contact is bad
2. Resistor mounted in the fan is open
3. The slow speed relay control circuit is not closing, from either the absence of ecu input or from a bad radiator temp switch
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Last edited by bazar01; 08-05-2011 at 04:37 PM.
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Old 08-05-2011, 06:24 PM   #10
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Anyone have the part number for the high speed relay? I just went out and checked my car, fan only comes on with A/C.
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Old 08-05-2011, 06:41 PM   #11
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Here you go. Assuming this purple one is really it!
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Old 08-05-2011, 06:53 PM   #12
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Ok well now I feel dumb, lol, I should have realized it was printed on the darn thing. Thank you Cirrus, you are always a great help.
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Old 08-06-2011, 08:42 AM   #13
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Mine doesn't run low-speed.
It only runs on high-speed I guess mine needs a new relay.
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Old 08-07-2011, 06:33 PM   #14
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I did replace the HS relay along with the dual-temp radiator sensor switch, and no low speed. (Does anyone know if you can still do the override for the lowspeed from the sensor plug? The HS does override fine.
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Old 08-09-2011, 05:46 PM   #15
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Do it on the relay/fuse board in the fuse box under the hood, just like in this link here that he does on the ABS relay; http://www.318ti.org/forum/showthread.php?t=14322


But make sure to identify the right LS relay and the right 30 and 87 pin sockets on the board cause they are not the same location as the ABS's above though.

Here below is my 1994 318 sedan fuse box layout. The LS relay location is #15. I’m not sure whether is it the same as your guys’ ti?


And here my new LS relay replacement p/n 6136 1389 105


However, this bridging does not tell that there is no faulty over the trigger wiring harness form the sensor to the dme and from the dme to the relay nor the relay is good since we have override them all. It just tells us the fan and the fuse are good though.

The way to test the relay is just switching the LS relay to the A/C compressor relay or #14 in the fuse box layout above, if they both are the same as those of mine, and test run the A/C. If the compressor works properly, the relay is good.

The way to check or override the LS signal is kinda tough though. You have to rewiring the trigger harness.

1st, tap on the LS trigger / green stripe or whatever color from the sensor socket cable.

Then undo the fuse box upper housing. There will be 4 hex screws that hold it as the realoem layout below:



Next, locate and tab the other side of the rewiring cable on the 85 pin socket wire under the relay/fuse holder board.

Do you guys follow me?

Last edited by 9G3Series; 08-09-2011 at 06:11 PM.
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