Code p1780 O/D light blinking | Ford Explorer Forums - Serious Explorations

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Code p1780 O/D light blinking


New Member
June 12, 2008
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Year, Model & Trim Level
97 sport
I got a 97 explorer sport edition and while scanning it, a p1780 came up. O/D light is also blinking.

While driving it shifts to 4th gear and the rpms keeps climbing. Im at 40mph and the rpm is at about 5-6k.

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The code P1780 is set when you do not cycle the TCS switch ( the overdrive cancel switch) during the KOER test.

so the p1780 doesnt come on during normal driving condition, only when you do a selftest.

I forgot to also mentioned that the car doesnt even downshift when im letting off the gas completly when im going 40mph at 5k rpm.
When the O/D light is blinking there are no codes being thrown, the only ones I see are about the O2 sensor heater curcuit.

Ran the KOER test and the p1780 came up.

You can readjust the Transmission control sensor right? or is that the shift cables going to it?
How do you put it to "OD" position?

Here is the description from the service manual. The TCS is just the switch on the end of the gearshift selector that turns off (or on) the overdrive.


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I redid the koer test and press the o/d switch and the switch does work since it didnt return the code.

Does anybody know why it doesnt go into o/d. Can it be the pcm?
And still no codes.

No, unfortunately I don't know why it refuses to shift to overdrive. It could be a mechanical problem or an electrical problem.

I would check the level and condition of the ATF, change it if it looks dark or smells burnt. Check wiring harnesses visually to make sure that they are not damaged/disconnected.

If you don't see anything obvious, you may want to look for a good trans shop for diagnosis.

Good luck.