Mechanics

VEHICLE WILL NOT GO IN GEAR WHEN HEATER IS ON

2004 Ford Explorer • 103,000 miles

If heater is off, car goes in gear fine. When heater is on, it won't come out of park? What on earth could cause this? I'm not sure if it is electrical related to the heater fan because it does the same thing when the A/C is turned on. If you turn on the A/C the vehicles transmission won't engage in any gear either. So A/C and Heater engagement causes the transmission to keep from shifting. The vehicle shifts fine while driving and you can use A/C or Heater. Put it in park and it won't re-engage until you turn off the A/C or Heater
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Alphaomega
June 5, 2013.



I have to be honest. In 30 years of working on cars, this is the first time I heard this. Lol The two components are not tied together. The park lock solenoid is actuated by power through the brake light switch (not the HVAC system). When it happens, I need you to check to see if the brake lights are working. If they don't come on, then there is now power to the brake light switch or solenoid. Let me know what you find.

Thanks for the reply! Here's another curve ball for you. It acts like the issue is in the control switch, the switch that changes where the airflow is sent. When it is in the off position the Driving Lights Go Off and you can change gears, when you are in any other position the driving lights come on, but you can't shift from park. The break lights work fine. I've never seen anything like this either. Thanks for your help.

Tiny
Alphaomega
Jun 5, 2013.
It sounds like the car is haunted. Maybe we need a priest. Lol WOW, you got me on this one because the vent door actuators are run by vacuum and not electric. Have you had a mechanic look at it yet?
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Thanks for the reply. I was thinking the same thing. This thing is haunted. My technical knowledge is limited to AC systems and finding hidden electrical Issues. Which I believe this vehicle has. A ground issue in the wiring harness is my first guess, the PCM is my second. You have helped alot. I don't feel stupid anymore. So many times things like this are due to something simple. I will put two of my other mechanics to investigate the issue when they come by. Sometimes it takes two or three to figure out this kinda thing. I do want to tell you what we figure out, once we finish diagnostics. Thanks so much again for your help.

Tiny
Alphaomega
Jun 5, 2013.
Let me know what you find. I would like to know.

Thanks,
Joe

The second mechanic spent 15 minutes under the hood and found that the blower resister was bad causing the crazy transmission problem. Hope this helps someone : )

Tiny
Alphaomega
Jun 7, 2013.

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