Air conditioner, check engine light etc

Tiny
MWC6628
  • MEMBER
  • 1998 MERCURY MYSTIQUE
  • 135,000 MILES
1998 Mercury mystique 2.0, I have replaced wiring harness, pcm, thermostat, temp gauge sensor, fan sensor and here is the problem. The check engine light is on showing bank one lean. Now here is another problem when you hook up the wire to the fan sensor the air conditioner stops working and the fan runs at the high speed. Unplug the wire and air conditioner works. I have tried everthing I know to fix but no luck HELP
Wednesday, March 28th, 2012 AT 1:15 AM

24 Replies

Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
For the CEL, have it scanned for all codes, soft and hard.

I'll have to see if someone else can help you with the AC problem. But I would check that wire to see if it's grounded anywhere. Our reference source is being mean to me, so I can't see wiring schematics.
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Thursday, March 29th, 2012 AT 8:04 PM
Tiny
MWC6628
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I am sorry when you unplug the sensor the fan runs on high even if the engine is cold and the ac works good but cycles on the compressor, when you plug it back up fan runs normal but ac does not work runs for about 15 seconds then shuts down. Had them backwards sorry.
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Thursday, March 29th, 2012 AT 8:17 PM
Tiny
RASMATAZ
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Is this fixed yet or what?
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Thursday, March 29th, 2012 AT 8:20 PM
Tiny
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The cooling fan runs on high? Or the AC blower fan, blowing air into the passenger compartment?

By "sensor" I presume you mean the coolant temperature sensor in the block?

No, ras, not yet. Mit1 isn't letting me look at circuit schematics or diagrams for this vehicle.
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Thursday, March 29th, 2012 AT 9:20 PM
Tiny
WRENCHTECH
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You need to be more specific about what sensor you are unplugging because that car doesn't have a fan sensor. Do you have a scan tool to access temp data from the computer.
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Thursday, March 29th, 2012 AT 10:31 PM
Tiny
RASMATAZ
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Mit1 won't give up the schematics
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Friday, March 30th, 2012 AT 12:34 AM
Tiny
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Bless AllData! Thanks Wrenchtech.
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Friday, March 30th, 2012 AT 12:47 AM
Tiny
WRENCHTECH
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No problem. Let me know if you need anything else. This one's going to be hard to instruct.
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Friday, March 30th, 2012 AT 12:50 AM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Having the schematic will make it easier than not having it.
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Friday, March 30th, 2012 AT 4:00 AM
Tiny
RASMATAZ
  • MECHANIC
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Now were cooking -Where's the beef at
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Friday, March 30th, 2012 AT 9:42 AM
Tiny
MWC6628
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  • 9 POSTS
It is the Sensor located on top of the thermostat housing that controls the pcm, the radiator fan speed not the blower that runs the passenger compartment. Under the thermostat housing is the sensor that controls the tempature gauge, it is the one on top that you can plug up and unplug. That is about as specific as I can get.
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Friday, March 30th, 2012 AT 12:28 PM
Tiny
WRENCHTECH
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That is the coolant temp sensor for the computer and it has no direct connection to the fans other than feeding temp info to the computer which then makes it's own decisions. Unplugging it sends the computer into default which automatically turns the fans on. As I stated before, you need a scan tool to access what the computer sees as temp.
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Friday, March 30th, 2012 AT 12:34 PM
Tiny
MWC6628
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Shoot with a temp gun on the neck runs 190 to 192 degrees just under the sensor and the thermostat neck.
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Friday, March 30th, 2012 AT 12:39 PM
Tiny
WRENCHTECH
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No mwc6628, that won't tell us what the computer sees and that's what I need to know.
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Friday, March 30th, 2012 AT 12:41 PM
Tiny
MWC6628
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Ok will be later before I can get it scanned. More Money for this diagnostic.
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Friday, March 30th, 2012 AT 3:30 PM
Tiny
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Call around. Many shops will do this for free.
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Saturday, March 31st, 2012 AT 7:30 PM
Tiny
MWC6628
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  • 9 POSTS
The code going back to the PCM is PO118 Coolant Temp Sensor HIGH Input. Again with the plug off the Temp Coolant Sensor the AC works good but the Radiator Fan runs high all the time. Unplug the sensor Radiator Fan runs normal but you lose the AC Compressor turns for about 7-8 seconds and cuts off. Hope this helps and what you were looking for.

THanks
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Thursday, April 5th, 2012 AT 5:35 PM
Tiny
WRENCHTECH
  • MECHANIC
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The fan always defaults to on when the sensor is unplugged. That's what sets your code too so stop doing that and diagnose it right with a scan tool as you were advised.
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Thursday, April 5th, 2012 AT 6:10 PM
Tiny
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Please.
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Friday, April 6th, 2012 AT 3:22 AM
Tiny
MWC6628
  • MEMBER
  • 9 POSTS
I do not need your assistance anymore, it was the relay in the fuse box located on the fender well. The car is running fine now and everything is working accordingly.
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Thursday, April 19th, 2012 AT 1:52 PM

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