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Old 09-01-2012, 07:43 PM
Junior Member
Join Date: Aug 2012
Location: Northern Colorado
Vehicle: 1999 Ford F150
Posts: 8
TCIL light

I have searched on here and found a lot of good info on flashing tcil lights.

I put new tires all the way around on my 99 F150 screw 4x4, and on the way home from the tire shop, tcil started flashing.

Went from 245/75/16s to 285/75/16s.

Could this tire size change be the cause of the tcil flashing?

I plan to get the codes asap, but thought I would ask this question first.

Truck has 141000 miles on it. Only owned it for 4 weeks now.

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Old 09-02-2012, 05:09 PM
Junior Member
Join Date: Aug 2012
Location: Northern Colorado
Vehicle: 1999 Ford F150
Posts: 8
Hey, Tony.
I can help you with that. If you remove the negative side of your battery cable, it will reset the PCM and your truck will now operate without the TCIL light blinking.

It's a simple fix. Hope this helps.
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Old 09-07-2012, 06:21 PM
Join Date: Aug 2009
Location: ?
Vehicle: 2004 Ford F150
Posts: 82
Tire size does effect shift points. The ecm does know what size tires. Period. Good bye
04 F150 4x4 Screw Lariat 5.4 3v | 3.73's | K&N C.A.I. w/12in air cleaner | Pacesetter Lt's & 3" off road Y pipe | 18" Borla 3"s/i-2.5"d/o, 4" Borla tips | SCT Pro Racer X3 tuning | IMRC's Removed | Comp Cams 127400 | Comp Springs | Phaser limiters | Weapon X stage2 coils | SVT high volume/pressure oil pump | SVT 34lb/hr injectors | Self Built 4R75W, with PATC 13xx 2500 stall conv. & SFI 29.1 aproved flywheel
Former Ford Tech

Last edited by BobFinnell; 09-08-2012 at 05:54 PM. Reason: BLAH
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Old 09-07-2012, 10:41 PM
Senior Member
Join Date: Mar 2000
Location: SE Florida, USA
Vehicle: 2002 Ford E350
Posts: 1,509
The PCM doesn't know what size tires are on the truck. Reprogramming the tire size is only to correct the speedometer and the odometer. It won't affect the shifting. Changing to larger tires can't make the TCIL blink. Disconnecting the battery will erase the code, but it won't fix what's wrong. The light will come on again if the problem is still there.

You need to take it to a shop that can read the codes. Most independent shops and all Ford dealers can do it. The auto parts stores that read codes free can't read Ford transmission codes. Don't go there.

Former Ford Automatic Transmission Engineer, 1988-2007
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