Electrical assistance needed - N46 cooling pump

[enuff_zed]

I've very quickly got to the limit of my understanding and need some electrical assistance please.
N46 2.0i engine has an auxiliary water pump mounted under the air box. A hose runs into it then out to the heater, from there back to the expansion tank.
I have no hot air in the cabin at all.
I found the hoses to and from the heater to be cold. The hose running to the auxiliary pump is getting hot, but not its outlet.
I have discovered there is definitely 12v going to the pump plug with ignition on '2'.
I have also wired the pump across a battery and it runs fine.
I have done the same with a second pump. That works fine across the battery too.
Both pumps have been fitted into the car. I know they both run on 12v and I know 12v is coming out of the plug.
BUT............... neither pump will run.

What am I missing? Don't think it needs water pressure as they run across a battery ok?

I am no electrician, so although something i the back of my mind is telling me I need amps as well as volts, I have no idea how to go about checking this! Or am I barking up the wrong tree?

Help?

[colb]

Got to be an impeller inside the pump to force the water through it, the fact that you can hear the motor working makes me wonder if the impeller is not being turned by the motor spindle hence no flow or maybe the heater matrix is blocked preventing flow.

[enuff_zed]

Got to be an impeller inside the pump to force the water through it, the fact that you can hear the motor working makes me wonder if the impeller is not being turned by the motor spindle hence no flow or maybe the heater matrix is blocked preventing flow.

Nope, both motors spin fine when across a battery, and I can see the impeller turning in both of them.
But connect them to the car loom, which definitely has 12v at it and nothing happens. Weird.

Had a similar issue with a washer pump on an old Capri years ago. Showed 12v but wouldn't work. Discovered the spade connector at the fuse box was corroded which must have caused a high resistance. Cleaned it and it worked fine.
So I'm wondering if it's a similar issue here. Not sure here I start though? Tempted to run an ignition live to it, with a new plug, from somewhere else.

Tomorrow's job is to use a spare battery to power the pump on the car and see if it will run in situ and cure my lack of heat at least.

[deltasierra]

https://bimmerprofs.com/electric-waterpump/

Maybe this explains more,

[smorris_12]

Generally it's easier to switch the ground side of a circuit so devices get a permanent 12v and have the 0v/ground side switched. So seeing 12v isn't surprising.

[enuff_zed]

Generally it's easier to switch the ground side of a circuit so devices get a permanent 12v and have the 0v/ground side switched. So seeing 12v isn't surprising.

Hmmm, but I thought that putting my voltmeter across the two pins of the plug and getting 12v must mean the circuit is complete? I’m got checking from one pin to earth?

[enuff_zed]

https://bimmerprofs.com/electric-waterpump/

Maybe this explains more,

Thanks but this seems to be for the main pump? My issue is the auxiliary pump that circulates coolant to the heater. I have no codes and have fitted another pump too.

[smorris_12]

Hmmm, but I thought that putting my voltmeter across the two pins of the plug and getting 12v must mean the circuit is complete? I’m not checking from one pin to earth?

Because test meters are very high impedance the smallest amount of current to ground thru the controller will give you a reading. All it takes is a large resistor being used in the "Pump Open Circuit" test circuitry passing a few microamps and you'll get your voltage reading.

Similarly, a high resistance joint as per your Capri would do the same thing. Enough current to give a reading but nowhere near enough to drive a motor.

You could try substituting a 5W bulb for the motor which would eliminate any mechanical problems and let you see if the circuit is being switched correctly.

[enuff_zed]

Hmmm, but I thought that putting my voltmeter across the two pins of the plug and getting 12v must mean the circuit is complete? I’m not checking from one pin to earth?

Because test meters are very high impedance the smallest amount of current to ground thru the controller will give you a reading. All it takes is a large resistor being used in the "Pump Open Circuit" test circuitry passing a few microamps and you'll get your voltage reading.

Similarly, a high resistance joint as per your Capri would do the same thing. Enough current to give a reading but nowhere near enough to drive a motor.

You could try substituting a 5W bulb for the motor which would eliminate any mechanical problems and let you see if the circuit is being switched correctly.

Thank you.
I'm away for a week now, but will try that on my return.
Newtis circuit diagram seems to suggest power comes from Fuse 10, through the motor then on to the AC controls.
Fuse looked ok, but I swapped it for a new one to be sure.
So I'm wondering if maybe there could be a fault within the switch assembly on the dash.

Anyone know if pre- and post-facelift heating controls are interchangeable? I know the knobs look different, but i have an early one spare that I could slave into this facelift car as another check.

[enuff_zed]

Well a random comment by bigwinn sent me off at a tangent and I found this old thread
viewtopic.php?p=1381879&hilit=hedgehog#p1381879
No idea exactly how the 'hedgehog' cured the heater from only blowing cold, but I have a spare and am going to slot that in whenever the missus stops giving me jobs to do!
I am hoping it somehow signals the auxiliary pump, but it's not hard to get at so worth a punt.

[smorris_12]

Reading that thread it sounds a bit specious (or misremembered) to me. The FSR is merely a PWM motor controller and (certainly on an E36) has no feedback to the heating controller. Feedback is provided by the cabin temperature sensor. Asking a motor controller its opinion of cabin temperature is akin to asking the fighty drunk in the pub for his opinion of Kwase Kwatang's special fiscal operation.

I can't bring up the WDS on this laptop (grrr, Java trying to protect me from something) or I'd check out exactly how the system works. Traditionally there was always a solenoid controlled water valve to modulate the cabin heat. I don't know if this has been superceeded by having a pump alone or if it's in addition. But that's where I'd start.

[enuff_zed]

Right then!
Today I delved into the dash and firstly discovered someone has been there before as there was no Air Mixer Flap Actuator fitted!
What a pig that is to access! Luckily I had a spare and managed to get it in to place.
The Hedgehog had to come out for access so I swapped another one in.
Then while I was at it I managed to somehow reach the heater temperature sensor and swap that.
Finally, slaved in another control panel.
No change! Auxiliary pump will not run!

Anyone got any ideas?

Thinking my next step is to rig a separate supply to the pump and see if it runs, sends hot water to the heater and gives me heat in the cabin.
If that works then I think I'll simply make up a length of loom and run it to the pump from a suitable ignition live.

[N4LLY]

Take it to a BMW main dealership

[enuff_zed]

Take it to a BMW main dealership

Yo-ho-ho!
Never!!!

Its a cheapo 4-pot. If I can jury rig it I will.

[N4LLY]

Take it to a BMW main dealership

Yo-ho-ho!
Never!!!

Snigger