Cooling fan trouble

HAVAI

MEMBER
2000 PONTIAC MONTANA
3.4L
6 CYL
2WD
AUTOMATIC
191,000 MILES

Hi. On my van (similar to the Venture), the cooling fans are not operating properly. (Causing the engine to run hot in the summer, especially in stop and go traffic.) The driver side fan does not come on ever, and the passenger side fan comes on only after the vehicle reaches very high temperatures (above 260 or so) or when the A/C is on. Over the past year, I have changed the coolant temperature sensor and the thermostat (twice actually). I know that both cooling fan motors work, as they come on when directly connected to the battery. I have changed all three relays, and the fan fuses appear good. Of note, when I disconnect the temperature sensor (with engine running), only the passenger side fan comes on (the driver side fan does not). I did detect what appears to be modest heat stress, slight melting at the end of one of the wiring harness connectors, at the junction with the fan assembly. I suspect a wiring issue, but how do I test for that? (And please do not tell me I can only do so with a pro scan tool)

6 Replies

HAVAI

MEMBER
4 POSTS

Typo in my original question: the passenger side fan seems to come on when coolant temperature passes 220 (not 260) degree F or so. (Just before getting into the "red" zone)

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Wednesday, July 4th, 2018 AT 5:12 PM

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

First. Key on engine off, remove the temperature sensor connector. The fan that does not work, check for power at the connector with a volt meter or test light.

If you have power, then replace the connector. They are available at a parts store and cheap to buy.

If you have no power, then you need to check the fuse listed for the fan in the diagram I attached. Verify power on both sides of the fuse.

Roy

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Thursday, July 5th, 2018 AT 8:59 AM

HAVAI

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4 POSTS

Thanks Roy for the reply and wiring diagram. With power on, I did check for power at the connector at the malfunctioning fan, #1, on the driver side. (Again, this fan works when tested with direct power, but not in its normal connections). No power at that connector (where it connects to the fan motor). I then checked the corresponding "maxi fuse" (slot #6). Fuse continuity good. Power verified on both fuse sides.
I also checked carefully for power at the connector to fan #2 (passenger side). It too had no power at the connector at the fan motor, and its corresponding fuse also okay, with power verified in fuse socket (both sides).
One other detail to add from my original write-up. I understand a switched on A/C ordinarily should trigger the fans (both of them) to come on, even when the engine is cool. That is not happening now. The passenger side fan (#2?) Only comes on when the engine temperature passes 220 or so.
I will be grateful if you have any further diagnostic suggestions.

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Sunday, July 15th, 2018 AT 4:03 PM

ASEMASTER6371

MECHANIC
52,797 POSTS

The AC system should trigger the fan when the high side pressure hits 150 lbs. Does the AC system work?

The other fan is working correctly.

Check the pressure first on the AC system. Then we will have to do some wire checking.

Roy

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Sunday, July 15th, 2018 AT 8:39 PM

HAVAI

MEMBER
4 POSTS

Many thanks Roy for your earlier tips and help with this vehicle. Quick update and a follow-up. You were correct that I also had an A/C system issue, and I have corrected now. I also was able to rebuild (new connector+) the previously melted wiring harness at the junction spot where it divides off to the two fans. So the good news is that both fans now work at both low and high speeds and come on when keyed to engine temperature. However, the fans are not coming on when the A/C is switched on. (The A/C clutch is spinning and the compressor appears to be functioning) I gather there may be a sensor somewhere that directs the cooling fans to come on when the A/C is running. If so, where is it? (I've seen references to a "high pressure sensor" on the high side line that controls the fans, but is there anything like that on my vehicle listed above?)