Transmission Issues P0758!

[BillHill93]

I know that this code has been discussed numerous times. I can't seem to find a definitive answer on what my next step should be. 2005 Yukon Denali with vortec 6.0 and 4L65E transmission. Sometimes I can drive over a hundred miles with no issues. Other times after driving 10 miles I'll get a CEL and the engine will rev up while trying to shift from third to fourth. Sometimes it will lose fourth gear all together. Sometimes it will lose first gear all together. Sometimes the CEL will go out on its own and it'll drive fine for a while. I tested both the a and b solenoid and they tested good. Fluid looked clean. I'm wondering if a valve is sometimes sticking and if a transmission flush would be a good idea?

 

[rockola1971]

B solenoid or its associated wiring or sticking associated valve(worn valve/valve body bore or dirty fluid causing valve(s) to hang up in bore of valve body.

 

[BillHill93]

B solenoid or its associated wiring or sticking associated valve(worn valve/valve body bore or dirty fluid causing valve(s) to hang up in bore of valve body.

Thanks for the reply. I changed the fluid and filter. The fluid was clean. No metal shavings in the pan. I tested the b solenoid for function and resistance and it checked out. I replaced it anyway thinking that since it was giving me that code I might as well. The problem still persists. I have read where some people have said that a bad throttle position sensor can cause erratic shifting. I've had the vehicle for about 5 months now. It's got 135,000 mi on it. I'm kind of surprised that it's having issues with no more miles than what is on it and was hoping that a transmission flush might fix it. Maybe I should take the pan back off and inspect the valves.

 

[NickTransmissions]

Thanks for the reply. I changed the fluid and filter. The fluid was clean. No metal shavings in the pan. I tested the b solenoid for function and resistance and it checked out. I replaced it anyway thinking that since it was giving me that code I might as well. The problem still persists. I have read where some people have said that a bad throttle position sensor can cause erratic shifting. I've had the vehicle for about 5 months now. It's got 135,000 mi on it. I'm kind of surprised that it's having issues with no more miles than what is on it and was hoping that a transmission flush might fix it. Maybe I should take the pan back off and inspect the valves.

This sounds like a C2 issue (command and control). Stick a bidirectional scan tool and take it for a test drive to see if the pcm is commanding this sort of shift pattern and why. It could be tps, maf or pcm itself. Shift sol B is off in 3rd and 4th, shift sol A is on in first and fourth so if you're losing both 1st and 4th on a recurring basis, sol A may be intermitteningly malfunctioning or the harness (transmission internal or external vehicle harness) could have an intermittent short or similar fault.

 

[BillHill93]

This sounds like a C2 issue (command and control). Stick a bidirectional scan tool and take it for a test drive to see if the pcm is commanding this sort of shift pattern and why. It could be tps, maf or pcm itself. Shift sol B is off in 3rd and 4th, shift sol A is on in first and fourth so if you're losing both 1st and 4th on a recurring basis, sol A may be intermitteningly malfunctioning or the harness (transmission internal or external vehicle harness) could have an intermittent short or similar fault.

Thanks for the info. Is there a way to test the TPS and the MAF sensor for proper functionality on the 6.0 vortec?

 

[NickTransmissions]

Thanks for the info. Is there a way to test the TPS and the MAF sensor for proper functionality on the 6.0 vortec?

Yep - see the post you quoted. If you dont have one, make the investment. A good scan tool enables you to perform a proper diagnosis vs just throwing parts (money) at the problem. Pays for itself after a couple uses. I believe you can also to some testing with a multimeter but not sure exactly how.

I plug in my SnapOn Verus whenever any of my vehicles begin to act up...

 

[BillHill93]

Yep - see the post you quoted. If you dont have one, make the investment. A good scan tool enables you to perform a proper diagnosis vs just throwing parts (money) at the problem. Pays for itself after a couple uses. I believe you can also to some testing with a multimeter but not sure exactly how.

I plug in my SnapOn Verus whenever any of my vehicles begin to act up...

Another question that you might be able to answer. Shouldn't there be a certain amount of resistance at the connectors that connect to the a and b solenoids? If so do you happen to know what the range of that resistance might be?

 

[NickTransmissions]

Another question that you might be able to answer. Shouldn't there be a certain amount of resistance at the connectors that connect to the a and b solenoids? If so do you happen to know what the range of that resistance might be?

Sol A&B, 3-2 solenoid: 19-24 ohms
EPC: 4-5.5 ohms
PWM sol: 9-12 ohms