No Speedo/No Shift

GEOFFA1971 · October 23, 2014

working on my 01 1500 4wd. having to give heavy throttle to even get a 1-2 shift. have been thru t-case and replaced all vss sensors. still no speed signal to gauge cluster or ecm. has anyone had this issue before? I am a vet mechanic but not in the business anymore. I have tried a lot and am losing this battle.

ifixedit · October 23, 2014

Although no tranny problems on my end, I've been chasing a few problems myself as of late and finding out they are all electrical / ground related since everything including the transmissions are electronically controlled. I recently read a report that water could get in under the dash and into the main body harness to gauge cluster connection causing the problem you describe, so I would look at that for sure for any signs of moisture, debris, corrosion, etc., this will be either right behind the gauge cluster or in the drivers side kick panel area. The more easy things to check first would be to remove the drivers side kick panel to see if water has gotten into any connections there. I'd also research any grounds pertaining to where they are located for the PCM and the transmission which you can usually find illustrations here on the internet by model and year. Depending on the year there are numerous possible trouble locations ranging from grounds on the back of the cylinder heads, back of the block near the back of the heads (both not easy to get to), or grounds under the drivers side door on the frame that go bad. Also take a look under the power box under the hood (the part holding the fuses and relays should flip open) for sign of mice getting in and chewing on wires. Is it showing any codes?

I hope you are able to get it figured out.

GEOFFA1971 · October 24, 2014

yes. p0502 which is "speed sensor low input" . I am gonna go through all grounds and look at those areas you spoke of today. what you recommended is different than the advise I had already gotten so that might be what gets it fixed. thank you. will let you know how it goes.

ifixedit · October 24, 2014

I did a bit of adding / editing here:

no problem, I hope it helps and is at least worth a look. It sure sounds like grounding or other connection problems. Look for all the black wires with white stripes you can find, these are the grounds. Do you know how to perform a voltage drop test on your grounds?

Even though this pertains more to another problem many GM owners experience, a poorly grounded PCM or other poor grounds / open circuits can cause all kinds of issues from the tranny not shifting correctly, to poor idle or stalling, gauges going crazy, etc., etc.

This proved useful in explaining how to do voltage drop tests and you might get a few ideas from it.

http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/electronic-throttle-body-4

I also found this but may be redundant info. Seems with the code you pulled the tranny will want to start out in 2nd gear when this problem happens and the engine will exhibit very sluggish performance which sounds like what's happening from what you describe. I also read the trans may simply be giving up the ghost, hopefully that's not what it is, I've found from my experience these trannys to be mostly bullet proof. I've got one with over 200K on it in a 98 Yukon, haven't even flushed it or changed the filter and it still works like new.

http://engine-codes.com/p0502_chevrolet.html

Wheel speed sensors not grounded good could be another issue causing the problem from what I've read. Is the ABS light on the dash on?

Also just curious, did this problem show up all at once unannounced one day, or did it come on gradually only showing up here and there and then got worse over time?