Cooling fans running all the time

Tiny
MKFARREN
  • MEMBER
  • 2003 DODGE NEON
  • 2.0L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 74,000 MILES
Both cooling fans come on within three seconds or so of starting the engine. Code p0481 on OBD. Fan relay and coolant temperature sensor have been replaced. No ground on 70 pin in relay box until engine is started. I have also tested with the AC high pressure and low pressure unplugged. No other error codes.
Monday, March 26th, 2018 AT 7:41 PM

58 Replies

Tiny
KEN L
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Hello,

It sounds like you have a fan cooling relay driver stuck on in the PCM and it will need to be replaced. I would try a used one.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Check out the diagrams (below).

Please let us know what you find.

Cheers, Ken
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Wednesday, March 28th, 2018 AT 12:21 PM
Tiny
MKFARREN
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Thanks, relay's already been swapped and the ECT sensor. The computer's turning the relay on after the engine is running (around three to five seconds) I had swapped in another computer as a test and get the same results. I have probed the relay plugs with a test light and no ground on the relay with key off or on until the engine starts.
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Wednesday, March 28th, 2018 AT 6:16 PM
Tiny
KEN L
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What is you unplug the sensor and start it up what happens?
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Wednesday, March 28th, 2018 AT 7:46 PM
Tiny
MKFARREN
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The fans continue to run. The only thing that keeps them from running is pulling the fuse or pulling the relay.
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+1
Wednesday, March 28th, 2018 AT 7:49 PM
Tiny
KEN L
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How does the HVAC system work no problems I am thinking it is sending a signal from the air conditioner to turn the fans on. Can you unplug the control head to see if the fans still run?
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Thursday, March 29th, 2018 AT 1:37 PM
Tiny
MKFARREN
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  • 36 POSTS
I pulled the dash controls for the HVAC and fans are still on. Also have unplugged the high and low pressure switches on the compressor and line. Is all I should have to pull is the harness from the switch panel correct?
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Thursday, March 29th, 2018 AT 5:37 PM
Tiny
KEN L
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The codes says there is a problem in the circuit. Lets do a pin to pin check on the coolant fan wiring to see what you can find. here is a guide:

https://www.2carpros.com/articles/how-to-check-wiring

Use the wiring diagram above.

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Friday, March 30th, 2018 AT 10:25 AM
Tiny
MKFARREN
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Thanks, I will try this tonight or tomorrow and post back results. I have been gone all weekend.
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Sunday, April 1st, 2018 AT 1:05 PM
Tiny
KEN L
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No problem, let me know.
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Sunday, April 1st, 2018 AT 4:08 PM
Tiny
MKFARREN
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Finally back to this in between weird WV weather. I have not found anything out of the ordinary in any of the tests.
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Thursday, April 5th, 2018 AT 6:55 PM
Tiny
KEN L
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It like the PCM is thinking the engine is overheating and you say you tested the wiring to the sensor? You may need a scanner that can read live data to see what the computer sees as engine temperature.
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Friday, April 6th, 2018 AT 11:22 AM
Tiny
MKFARREN
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  • 36 POSTS
Thanks, I did, also the temperature gauge is reading correctly if that makes a difference. Tomorrow after the snow is over I am going to search through the two sides of the relay again for a short to ground just to be sure I have not missed it. I tried a second computer that was a known good one and it shows p0481, too. Last night I worked all the way back through the wires in connector C104 in the lower left of the dash for the switches.
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Friday, April 6th, 2018 AT 4:29 PM
Tiny
KEN L
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It does sounds like you have a wiring issue. Below are the rest of the wiring diagrams for you.

Please let us know what happens.

Cheers, Ken
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Saturday, April 7th, 2018 AT 12:09 PM
Tiny
MKFARREN
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Thanks, I think so too. All of the wiring is stock, I cannot find anything modified or spliced. I will keep you posted. It may take a few evenings. I have considered a $50.00 engine harness from eBay just to see what happens.
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Saturday, April 7th, 2018 AT 3:28 PM
Tiny
KEN L
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Okay, it would be great to get you back on the road let me know.
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Monday, April 9th, 2018 AT 9:13 AM
Tiny
MKFARREN
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Thanks, yeah my teenage son agrees! I will be in Charlotte all weekend, but back on it Monday or so.
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Thursday, April 12th, 2018 AT 5:37 PM
Tiny
MKFARREN
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Okay, I am a couple weeks late, but back to the car. So far no change. I have not had a chance to start through the PCM harnesses yet. If I pull the plug on the y harness to the two fans, I get a p0480 and a p0481 so it recognizes an issue in both fan circuits. Plugged back in, I only get p0481. Should I start on the circuits that tell the PCM to turn the AC fans on?
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Wednesday, May 2nd, 2018 AT 7:39 PM
Tiny
KEN L
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Yes, that is where I would start.
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Thursday, May 3rd, 2018 AT 9:45 AM
Tiny
MKFARREN
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Question, would the PCM register an error if a short or bad sensor commanded the fans on?
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Thursday, May 3rd, 2018 AT 7:42 PM
Tiny
KEN L
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Yes it would, let run down this guide to let you know how.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

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Friday, May 4th, 2018 AT 11:01 AM

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