Electric fan resistance?

[Hunter79764]

I've got a DD 2004 Saturn VUE with the 2.2 and 5 speed stick. At idle, with AC on especially, it dims the lights and almost stalls out when the electric fan kicks on. It's a single fan, single speed (although the fan itself has 3 prongs, the harness only feeds it 2 wires). Fan seems to work fine, no overheating etc.
I know there's some weird electrical stuff going on (occasionally it loses power to almost everything, engine may or may not continue to run, I believe that might be a bad BCM and/or fuse box but it is too intermittent to diagnose yet), but I thought I might be able to figure something out on the fan. I checked resistance on the fan motor. All prongs show 0 ohms (yes, meter was on the right scale). Sometimes it would flash a few ohms as I was getting contact on the prongs, but always levels out to 0. I tested a known good fan motor I have (one side of some dual truck fans, can't physically swap but I jumped wires over to make it work), and the pull down when fans kicked on was nowhere near as severe. But the fan is a smaller diameter, and shouldn't pull as much power anyway. Ohms on that one were something like 1.9 ohms on high speed and 3.something on low speed circuit.

I can't see how there's 0 ohms on the fan motor but it works without popping fuses. I don't want to spend $80-120 on a new fan just to see what would happen, but maybe I can find one of these in a wrecking yard. Any advice until then?

 

[Snoots]

Disconnect your battery +. Measure the ohms from the + connector to the starter solenoid (big terminal), then measure from the + terminal on the solenoid (Small terminal) to the power distribution post.
You should have very few ohms on either. I'm thinking that those wires are about shot and should be replaced or you have a bad/loose connection.

 

[Camar068]

ohms on an electric motor is very close to zero depending on how many windings it has. In general, less that 10-20 ohms on a motor is good.

 

[Hunter79764]

I know it should be low ohms on the motor, my good motor is around 2 for high speed. But this one is 0.0 ohms once it settles out. I can't see how that's right, but I can't see how it would work with 0 ohm, which is why I'm so screwed up on this one...

 

[Snoots]

If it is a brushless dc motor the reading will be VERY low.

 

[Camar068]

I know it should be low ohms on the motor, my good motor is around 2 for high speed. But this one is 0.0 ohms once it settles out. I can't see how that's right, but I can't see how it would work with 0 ohm, which is why I'm so screwed up on this one...

how are you reading ohms with power to it?

 

[SquareRoot]

Bad ground. Fix and report back.

 

[Hunter79764]

Ohms were measured without power applied, directly on the terminals of the fan motor. I rechecked and rechecked, and ended up with 0.1 ohms on high sped circuit and 0.3 ohms on the low speed. Still seems wrong to me, but I don't know for sure. Apparently before I was not testing right, this time the car was cool and I could reach my head in closer to make sure the probes weren't touching anything except the terminals.
Grounds are not great but not bad, a 1-2 ohms each between fan ground wire and chassis, engine and chassis, chassis and battery, etc. (I'm pretty sure there was a bunch of salt in this car's past, I'm not used to that being in Texas). Similar resistance on positive components (fuse to battery etc). I was able to back-probe the connector when the fans kicked on, I get an initial dip to around 12.6 or so (hard to see on a digital meter, but that was about the lowest number after a few cycles) that leveled off to 14.4 when the battery terminals test about 14.5-14.6, so running load seems normal when I was testing it. Similar voltages at the battery terminals, not more than 0.1-0.2V anywhere, any time, and often within 0.01V.

I think I've got internal fuse box issues that are temperature dependent that might explain this one and some other power issues, mainly some intermittent power failures that seem more frequent in hot weather and high electrical demand. I was thinking the fan draw was the root, now I think it is just a symptom of the same disease elsewhere.
I'll dig in on that and see what I can find. I remembered a similar issue on my dad's 2005 Corvette. Thought it was fuel pump, turned out to be hot fuse box distribution issues, which was apparently a problem around this time for GM?

 

[Camar068]

Ohms were measured without power applied, directly on the terminals of the fan motor. I rechecked and rechecked, and ended up with 0.1 ohms on high sped circuit and 0.3 ohms on the low speed. Still seems wrong to me, but I don't know for sure. Apparently before I was not testing right, this time the car was cool and I could reach my head in closer to make sure the probes weren't touching anything except the terminals.
Grounds are not great but not bad, a 1-2 ohms each between fan ground wire and chassis, engine and chassis, chassis and battery, etc. (I'm pretty sure there was a bunch of salt in this car's past, I'm not used to that being in Texas). Similar resistance on positive components (fuse to battery etc). I was able to back-probe the connector when the fans kicked on, I get an initial dip to around 12.6 or so (hard to see on a digital meter, but that was about the lowest number after a few cycles) that leveled off to 14.4 when the battery terminals test about 14.5-14.6, so running load seems normal when I was testing it. Similar voltages at the battery terminals, not more than 0.1-0.2V anywhere, any time, and often within 0.01V.

I think I've got internal fuse box issues that are temperature dependent that might explain this one and some other power issues, mainly some intermittent power failures that seem more frequent in hot weather and high electrical demand. I was thinking the fan draw was the root, now I think it is just a symptom of the same disease elsewhere.
I'll dig in on that and see what I can find. I remembered a similar issue on my dad's 2005 Corvette. Thought it was fuel pump, turned out to be hot fuse box distribution issues, which was apparently a problem around this time for GM?

ok simple solution would be to put a relay on the fan. Use the current positive going to the fan as the positive control SIGNAL to the relay. Then wire in positive from a good source (typically the battery). problem solved. ~$10 and 20 minutes if you know what your doing and ur done.