Flashing O/D light when braking.

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Oct 29, 2011 | 07:30 AM

C.dog

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Joined: Jan 2011

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Flashing O/D light when braking.

I have a '94 F250 ext.cab4x4 with a 7.3 IDI and E4OD trans.
On braking the O/D off light flashes but as soon as the truck stops it goes off again.
This puzzles me a lot sinse the trans shifts smooth and flawless.
Oil and filter on the trans is changed and the problem is stil there.
Anyone who have a clue what causes this???

Oct 29, 2011 | 09:07 AM

86f250XLT-4x4

Elder User

Joined: May 2011

Posts: 973

Likes: 2

From: Bellefontaine, OH

From what I have read check your fuses make sure all your brake lights and turn signals work and go from there

Oct 29, 2011 | 10:27 AM

FORDF250HDXLT

Fleet Owner

Joined: Jul 2006

Posts: 20,360

Likes: 822

From: Mi'kma'ki

interesting.so its going back to normal mode from safety mode for you.i wonder if this is what happens when you have a brake light out then.hmmm.
any rate,i agree.id start by inspecting the brake light bulbs,BOO switch,and the wiring to the brake lights, in that order.

Oct 29, 2011 | 12:34 PM

Phy

Fleet Mechanic

Joined: Jan 2011

Posts: 1,709

Likes: 4

From: 8600 ft in Colo

What they said. The pcm needs signals from the brake light wiring to control the trans properly, and strange things can happen when it doesn't.
Also, you might see if there are any codes being stored...

Nov 1, 2011 | 03:59 AM

C.dog

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Joined: Jan 2011

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All fuses and lights works perfectly and no bulbs are shot.
All electrical wiring and connections is checked and cleaned both on the tranny and lights.
VSS is pulled out and cleaned.
Sinse the tranny shifts normal through all gears and the O/D OFF light flashes only when I push the brakepedal,it goes off *** soon I release the pedal again,I am thinking maybe the brakes are causing this.
Perhaps vacumleak somewhere as well?
Any ideas?

Nov 1, 2011 | 09:23 AM

IDI Diesel

More Turbo

Joined: Nov 2010

Posts: 668

Likes: 54

it wouldnt be the caused by a bad tail light as mine rarely work both at the same time. I have NEVER had an issue with my O/D light coming on.

Nov 1, 2011 | 09:50 AM

fuzzy1626

Cargo Master

Joined: Feb 2007

Posts: 2,477

Likes: 21

From: Taylorsville, NC

I wolud rule out anything to do with vacuum on an E40D. Would have to be electrical.

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Nov 1, 2011 | 07:51 PM

Coalroller

Posting Guru

Joined: Dec 2009

Posts: 1,615

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From: Hagerstown, Md

if not the BOO switch or brake related check your tach sensor. mine did the same thing at first. When i would let off the throttle and apply the brake it would flash but the second id give it a little throttle and i mean just barely tap it for like 50-100 rpm difference it would stop flashing. Then after a week or so of that it got a little worse the only time it would not flash was when the truck was at anything but an idle. As soon as id start the truck it would flash till i pushed the throttle down a hair with my hand. It turned out to be my tach sensor on its way out.

Good luck...