I'm working on a 2007 Ford Mustang. The O/D light is flashing and the transmission has some rough shift transitions.

When I use OBDII to read the codes, there are no faults found, no faults in storage.

Huh? Never seen this before. I would have thought that something that triggers a blinking OverDrive (O/D) lamp would set a code somewhere. Now my OBD2 scanner is sorta old. I think I bought it around 2008 or so. But it has always performed well.

Or is there a separate special systems tester of some sort to read transmission fault codes?

I'd like to understand why the lamp is blinking.

Note: the transmission has 120K miles, and I doubt the fluid had ever been changed. I pulled the drain pan, cleaned things up, no metal bits in drain pain. Replaced filter and what oil I can. Still shifts rough.

Anybody know how to read the code behind the blinking O/D light ?

1 Answer 1


Yep flashing O/D light indicates an error code logged for the transmission, there's about 100+ transmission codes so I wouldn't like to hazard a guess as to the cause but in theory it can be read with an OBDII scanner, unfortunately it does seem to be pretty hit and miss between different scanners for reading transmission codes on these depending on which protocols your scanner supports.

I've never used one personally but the Innova 3100i seems to come highly recommended for Fords.

  • There are Code Readers and Code Readers.... Got one for my car that was specifically matched for Landrover/jaguar - works as it should... Consider getting a specific one instead of a "generic chinesium" copy.
    – Solar Mike
    Commented Nov 5, 2018 at 11:48

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