Primary fan stays on all the time? - Chevy Impala SS Forum
 
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post #1 of 8 (permalink) Old 11-02-2015, 06:41 PM Thread Starter
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Primary fan stays on all the time?

I just installed the Innovative wiring kit for converting a mechanical fan car to dual electric fans (basically just adding the primary fan and wiring).

I have a weird problem: the new primary fan stays on all the time. Turns on with the accessory power on and doesn't turn off until the key is off. I have a code 77 for primary fan.

I emailed Innovative wiring and he had never seen this problem before and just suggested checking all my work. Everything appears to be hooked up correctly as per his instructions - anyone have an idea for what is going wrong here? If i pull the temp sensor connector at the water pump both fans go on as they should.

Thanks for the help!!
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post #2 of 8 (permalink) Old 11-02-2015, 09:35 PM
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Same as last week?

Take a look at this thread it may help.

https://www.impalassforum.com/vBullet....php?t=1273041

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post #3 of 8 (permalink) Old 11-02-2015, 10:58 PM Thread Starter
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awesome, could be similar. after looking at the diagrams and reading that thread, it could be one of the coolant temp sensors or the high pressure ac sensor...i'll check them all. Since it's a Roadmaster I can check the coolant sensors in the HVAC display and they both read normally. The other weird thing is the secondary fan comes on sometimes after I've been driving the car hard and come to a stop...coolant temps are fairly rock solid this time of year, expecially with the ac off. so it makes sense that one of the sensors is indicating more resistance than what really exists.
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post #4 of 8 (permalink) Old 11-03-2015, 11:02 AM
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Fans in traffic

If you can scan temperature on the HVAC display while driving you may be surprised what the PCM is reading compared to the gauge sensor.

When you go over a set speed (50mph?), AC pressure falls, or temperature falls the fans shut off. When you come to a stop the PCM may see a spike and turn on both fans.

I reprogrammed my fans to start sooner since my commuter route tops out at 50 mph but usually hovers around the factory turn on point (temp or speed) and the fans were turning on/off all the time. Now they stay on more and the temperature is more stable and I think the fans and relays will last longer because they cycle less.

DTC 77 and 78 are usually set by the relay being taken out and the key being turned on. A bad relay coil may set this code but this is not probable as your fans work. If you can clear it it will probably not come back.

You could search "fan start" for other threads with more solutions.

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post #5 of 8 (permalink) Old 11-03-2015, 12:39 PM Thread Starter
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Quote:
Originally Posted by Z09B4U View Post
If you can scan temperature on the HVAC display while driving you may be surprised what the PCM is reading compared to the gauge sensor.

When you go over a set speed (50mph?), AC pressure falls, or temperature falls the fans shut off. When you come to a stop the PCM may see a spike and turn on both fans.

I reprogrammed my fans to start sooner since my commuter route tops out at 50 mph but usually hovers around the factory turn on point (temp or speed) and the fans were turning on/off all the time. Now they stay on more and the temperature is more stable and I think the fans and relays will last longer because they cycle less.

DTC 77 and 78 are usually set by the relay being taken out and the key being turned on. A bad relay coil may set this code but this is not probable as your fans work. If you can clear it it will probably not come back.

You could search "fan start" for other threads with more solutions.
Thanks for the info - at least I know I'm on the right track! This morning I swapped to a good know high side ac pressure sensor (my ac system had a leak and is current discharged) and no change. No change either by unplugging the gauge sensor. I unplugged the water pump coolant sensor and both fans came on as usual and SES light came on. just like it should. I cleared the codes a few days ago and 77 was the only one to come back.


I had a buddy install the fan wiring and efans as I was too busy with work to complete this car a few months ago. I have checked his work as far as I can see without taking everything apart and it all looks correct. Only thing I can't see is under the relay box and the pcm where he installed the green signal wire. I will dig and check both of those later this week. I will also swap relays around and see if I can find if the primary fan relay is bad...it's brand new of course from the Innovative kit...
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post #6 of 8 (permalink) Old 11-03-2015, 01:10 PM Thread Starter
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one other thing - i monitored the two coolant temp sensor readings in the HVAC diagnostic mode and both have been completely normal. starting off cold and warming up to t stat opening temp....180 for the gauge sensor(option 8) and 95 celsius for the water pump sensor(option 24) which is in line with the water pump temp sensor reading about 20 degrees F over the cylinder head temperature.
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post #7 of 8 (permalink) Old 11-03-2015, 06:18 PM
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AC discharged compicates things

Swapping the relays will help with the DTC 77. If it becomes DTC 78 but the fans work or there is no DTC and the fans work there may be a resistor or diode inside the relay that is confusing the PCM.

Post your results on the relay swap.

If you know your way around the relay socket you should find coil +12 V (constant at key on) and the PCM switch (Grounds to turn on the coil) on relay pins 85 and 86. Or 86 and 85 the GM diagram is not standard to the relay pin numbers. The relay switches pins 30 87 you will find power on one of the two.

It sounds like it is wired correctly or it would not turn the fan on and off.

This leaves you with the headache of finding out why the PCM is grounding the relay and starting the fan.

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post #8 of 8 (permalink) Old 11-03-2015, 06:44 PM
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I looked at Gary's instructions

I did not know that the signal wire had to be added to the fuse box.

It might be time well spent to make sure the green signal wire is in the right spot in the PCM plug

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