96 chevy K1500 no tranny lock-up
 

Please help. 1996 Chevy K1500 5.7 (350). 160,000 Miles
VCU will not command lock-up on transmission.
Although transmission will lock-up on scanner request
Transmission has been completely rebuilt at 160,000 miles
Replaced ECU 3.670 (part #16244210 vcm-reman) twice and replaced module 2.383(part #16208981) in vcm
Still unable to communicate with vcm. Traced all wiring to vcm. Cleaned all terminals and connection.

Chevy Dealer has had my truck from 6/13/07-7/7/07. Snap shots have been taken while truck is moving and records strange data (ex. Driving in gear 256). They have been unable to solve lock-up problem. They have suggested that the vcm needs new programming directly from G.M. engineering.

Up-grades
3in. Rancho Suspension (33x15x12.5 BFG)
K&N air-intake
Dug Thorly Tri-Y headers
Genuine Gear 4.10 front and rear with rear ARB air locker
Air Lift rear air bag system with on-board compressor
Replace timing chain and installed high-volume oil pump at 160,000 miles
Tranny rebuilt and up-graded. At 160,000 miles
H/D trans rebuild
Torque converter rebuild
Z pack, 3-4
Force motor
Shift kit
Sun Shell update
Input sprag
U-joint-frt (RR driveshaft)
U-joint rear (rear driveshaft)
MLPS-OEM

Is there anything else that can be checked that might cause tranny not to lock-up?Thanks, Michael

RE: 96 chevy K1500 no tranny lock-up
 

Possibly the trans temp switch. It is part of the pressure manifold switch that bolts to the valve body. I believe the ecm won't command lock up till it heats up too operating temperture. Is it working correctly other than lock up? Someone didn't change your valve body with a 95 valve body by any chance did they? You should have a solonoid that is directly above the lock up solonoid that goes into the pump. If you pull the pan it will be on the driver side next to the filter. There should be one on each side of the filter as well as the lock up solonoid, but two that go into the valve body. Here's a list of all the solonoids you should have under your pan. Two shift solonoids, force motor, pressure manifold, 3-2 downshift soloniod, Pulse width modulator lock up solonoid, and lock up solonoid. Believe it or not I have had this same complaint with a 96 chevy and it was because the dealer installed a 95 unit. Maybe will get lucky and it will be the same problem.

RE: 96 chevy K1500 no tranny lock-up
 

Thanks so much for the info Alientranz. I will check thetrans temp switch tomorrow (7/10). I don't know if the valve body is a 95, but whenI drop the panI will make sure all solonoids are there and in the correct place. I'llget back to you this week.

RE: 96 chevy K1500 no tranny lock-up
 

The trans temp switch apperars to be working. The tranny is running about 177 degrees. The valve body was not replaced. One code keeps coming up on the scanner. PO 300 (I believethat means a random misfire in one of the cylinders but the PCU can't identify which one. So I changed the rotor, cap, wires and plugs (alloriginal AC Delco parts). Clearedapp and code (check engine light went off). Was able toget lock-up form tranny about 4 or 5 timesbefore check engine light came back on.I could not get lock-up after that. Same PO 300 code was strored in the PCM.

RE: 96 chevy K1500 no tranny lock-up
 

That's interesting. I didn't know a misfire would disable lock up, but it makes sense. When lock up applies it puts more load on the engine, so if you were having a misfire and lock up engaged you would really notice it. You would have to take to the dealership and ask them on that one and find out if a misfire disables lock up. If that's the case I guess you'll have to find out why you are getting a misfire.