transmission problems 4l70e

[Msamaniego]

just wanted to see if any one has any idea or clues in to why my trucks transmission would be acting up. it shifts from 1st to 2nd in a high rpm and then to 3rd just fine but not 4th gear, any ideas what it may  be or be causing it? the truck does give a code for a bad crankshaft sensor.

[sefiroxx]

Maybe in limp mode - internal sensor of and the e cu is limiting damage. High 1-2 could be accumulator failure. Clutches could be burned out. . . .

Need to take it in and check sensors, solenoid, pressures, fluid etc.