Transmission Won't Shift

[Blazer1996]

When the truck is first started from cold, the transmission acts like it's stuck in what I guess is 3rd gear. The check engine light comes on and the code reader reads "Shift Solenoid Electrical Circuit B" Truck is sluggish at startoff due to being in high gear but, runs fine at faster speeds although at highway speeds the RPMs are on the high side. After driving a while and warming up the engine, if I stop somewhere, when I start the truck a second time, the transmission shifts and works perfectly. It consistantly does this everytime. Hope someone knows what the remedy for this is.

Thanks,

Jay

[old_master]

Year, make, and model would be helpful. This could be an electrical problem however, how long has it been since the transmission fluid and filter have been changed? How many miles on the vehicle?

[Blazer1996]

This is a 1996 Blazer LS 4 Dr 4WD VIN W. Transmission fluid and filter changed at mileage 180400 on 12/17/05. Now has 189600 miles. Hope this will shed some light on the issue.

Thanks,

Jay

[old_master]

Was the code P0758? If so, were there any other codes set along with it?

[Blazer1996]

The code is P0758 , there are no other codes with it.

Thanks,

Jay

[old_master]

When P0758 is set, the VCM commands 3rd gear only and will not allow the torque converter to lock up. This explains both of your symptoms; “sluggish” from stops and RPM higher than normal at highway speeds. Diagnosis for this DTC is quite involved and requires some special equipment. There are however, some quick things that can be checked. The fact that it does operate properly after warming up may indicate a marginal electrical connection...somewhere. Pay close attention for poor or loose connections. If you are not comfortable with the following tests, don’t attempt them.

If the gearshift is column mounted, is the PRNDL indicator illuminated when the trans is acting up? If it's not illuminated, check the fuse: CLSTR fuse 11 is a 10amp fuse. It should be hot in the off, run, and start positions. Check it with a test light on both terminals; try moving it gently while testing it. If the light flickers, look for a loose connection.

Next step is check for power at the VCM. You must use a digital volt ohmmeter for this check. DO NOT use a test light. Cavity #17 is a pink wire; it comes from the fuse you just checked, (the same circuit that feeds the PRNDL indicator). Ground the negative DVOM probe and back probe cavity #17 with the positive DVOM probe. Must be within 1 volt of battery voltage. While the DVOM is connected, gently move the bulkhead connector, (interior and under hood) at the RH side of the dash (116 cavities) pay close attention to the pink wire. Again, if the voltage fluctuates, look for a poor connection. The connection through the bulkhead, and the fuse, are the only connections in this circuit, look carefully for loose connections.

This should keep you busy for a bit, post your results.

[Blazer1996]

Thanks Old Master! I think this will help greatly. I will keep you posted.

Thanks again,

Jay

[old_master]

Those tests only test for power to the VCM for the shift solenoid in question. If those check out ok, we can test the circuits to the shift solenoid.

[Blazer1996]

I doubt that there is any relation but, my fuel pump was replaced within a week of this problem surfacing. Common sense tells me that this is no where near the transmission and shouldn’t have anything to do with this problem. Please let me know if you think that this could be a factor in any way.

Thanks,

Jay