Blinking light randomization - Ford Powerstroke Diesel Forum
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Old 09-05-2012, 06:38 AM
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Blinking light randomization

1996 F250, auto, have had the infamous blinking OD light on the end of the shifter. When it is on, it shifts hard. Taking it to the shop today to pull the codes and I watched the light blink for the last time, then the truck ran great! So now the blinking light is intermittent??? The last time the light started I was headed down a 7% grade at 60mph, no throttle. This morning I tried to limit the hard shifts by starting in 2 and then shifting up to D. The speedo bounces, but only about 3mph when going above 65mph.

It is difficult to put all these seemingly random events in order but:
-Blinking OD light, started with downhill drive
-Bouncing speedo (only 3-5 mph) when at highway speeds
-Light stopped blinking and truck ran great this morning.

any ideas?
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Old 09-05-2012, 07:29 AM
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Bouncing speedo is the key. Your VSS is likely on the fritz. It provides the signal for the speedo, and provides speed "info" to the PCM to control the tranny. Flaky speed info ==> flaky tranny control. Remove the VSS and try cleaning it up, and inspect the tone ring inside the diff as best you can. Clean if possible. Check the connection on re-installation. Beyond that, either the VSS is shot or possibly the tone ring is damaged.
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Old 09-05-2012, 12:34 PM
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I have the same problem almost. My OD light just started flashing and the owners manual says that when that happens it a "critical fault" and the transmission goes into safe mode making it shift harder, changes shift points and will make it shift abnormally.
That being said, i have no spedo issues that seams to be working just fine but before the light started blinking it seamed to "slide" into grear rather than a strong shift. So what else would be considered a critical fault? I stoped and checked the fluid level and it was very low (barely on the dipstick) but when i added more fluid the light didnt stop blinking. Could it be a clogged port or filter? A wire shorting out?
i had to drive the rest of the way home and it stayed in "safe" mode but seamed to drive fine otherwise. Any ideas anyone?
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