Electronic speedometer and shifting probelms

ford
bronco

#1

The vehicle: 1994 Ford Bronco, 168K, 5.0L, metric OD transmission, electronic 4wd



The problem: The speedometer does not work, which, in turn, makes for shifting problems since the sensor for indicated speed does not get a signal and does not ?talk? to the transmission to ?tell? it to shift into 2nd, 3rd, OD, etc. Shifting takes place only after a long, steady speed at about 2000 RPM and with a slight lifting of the accelerator. The electronic odometer does not work.



I checked the appropriate fuse in the interior fuse panel (left side dash) for the speedo unit and have found no problems. Continuity test showed no problem. I pulled the instrument cluster and checked for loose/broken wiring/electrical connections; all checked out OK. Re-installed the panel, but the problem still remains. Checked wiring to the sensor on the transmission, that?s OK.



Since the thing will shift after lifting off the accelerator, I was reminded of shifting problems with older automatic transmissions that were cured by changing the transmission fluid. Just for drill, I changed the transmission fluid and filter, refilling with the proper type fluid. I didn?t expect this to cure a thing; it didn?t, but at least the transmission service was done.



Did I overlook anything? Another sensor or in-line fuse? I?m not working with any manuals or high-tech diagnostics, just old-skool thinking.


#2

Does this have a vehicle speed sensor ? If it does, that could be the problem.


#3

You checked the wiring to the sensor on the transmission, but did you check the output from the sensor?

This sounds like a faulty vehicle speed sensor (VSS).


#4

Yep, it sounds like a bad VSS.

It only takes a couple of minutes and a 30 buck scanner to pull the trouble codes.

Odds are you will get a code 452 "Insufficient input from VSS (vehicle speed sensor) to PCM.

On newer Fords the VSS plugs into the differential. On your 94 it probably plugs into the driver side of the transmission.

My Actron CP9015 works fine, but i do need to count the flashes.

Slightly more money gets a scanner that displays the trouble codes on the LED screen.


#5

@ mcparadise and 87 Ranger:

AHA!!! OK, I’m the dummy. Yeah, I looked at the wiring and connection to the VSS, but did not and could not check the output from the sensor. I will take a shot at it when the next spell of warm(er) weather gets here and I can mooch a scanner from a friend. Call it a couple of weeks.

Thanks, everyone.