1994 C1500 4L60E no shift and no speedo

[Briggsman]

I have a 1994 c1500 4L60E two wheel drive. Does not shift up and speedo doesn’t work. Pull tranny fuse and you can upshift and down shift manually. Cleaned trans electrical connector, new VSS, new ignition switch, checked fuses under dash, no codes. With tranny fuse in and key in run position, tested connector into transmission results as follows:
Black/yellow stripe 5v
Pink 12v
Red 12v
Blue 12v
Pinkish 12v
Purple-ground
Other wires: white, etc show nothing (voltage or continuity to ground)
Wondering if ECM could be possible issue. (When I set timing on engine to TDC then reconnected wire under glove box, computer advanced timing all the way past timing tab)

 

[NickTransmissions]

Replace the vehicle speed sensor, assuming nothings wrong with the sensor harness and its not simply unplugged for some reason.

 

[Briggsman]

Replace the vehicle speed sensor, assuming nothings wrong with the sensor harness and its not simply unplugged for some reason.

Had already replaced VSS

 

[NickTransmissions]

Had already replaced VS

OEM or aftermarket?

 

[someotherguy]

Wondering if ECM could be possible issue. (When I set timing on engine to TDC then reconnected wire under glove box, computer advanced timing all the way past timing tab)

Just to set your mind at ease on that behavior - it's normal. Plugging the bypass wire back in will advance roughly around 12° which will be off the tab.

I know you said you checked the fuses and it does sound like you've been pretty thorough, but did you actually pull the associated fuses and test them? Particularly the "gauges" fuse?

Richard

 

[Scooterwrench]

'93-'95 ran a DRAC or VSSB,may want to check that.

 

[Briggsman]

I checked for one of those VSSB’s….there’s not one there at all, just the connector.

 

[Briggsman]

I can’t find the smaller connector with the single wire anywhere.

 

[someotherguy]

I can’t find the smaller connector with the single wire anywhere.

A 1994 GMT400 doesn't use that other connector. I just looked through a bunch of pics from my (now sold) 1994 and it's a little hard to tell from most of the angles, but I don't see it - in this pic I'd cut a small hole in the glovebox compartment and poked the wires through so I can have the DRAC easily accessible. I'd modded it with DIP switches for recalibration, and also did several for other people, much easier for me to just throw it in there real quick to test it before handing it off.

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You definitely want to get the correct style for your truck, though. The one from a 1994 GMT400 has the two banks of jumpers instead of one.

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It's possible you'll find one that wasn't configured exactly the same as your truck came factory - axle ratio and tire size - so you may need to recalibrate. Easy and cheap if you can do basic electronics soldering; put in a couple banks of DIP switches.

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Richard

 

[Scooterwrench]

Single connector is the 4000 PPM signal for cruise control so if your truck doesn't have cruise there won't be that single connector. Those DRAC's/VSSB's are calibrated to you rear gear ratio so you will have to find one with the right calibration or re-pin it yourself.
Here is a good site with everything you'll need to know if you need to calibrate one.

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