98 Chevrolet Blazer 4.3L Transmission Issues with P0758 Code and Shift Problems

Model: 98 Chevrolet Blazer Fault Code: P0758 Posted: 2016-02-23 12:45

My 1998 Chevrolet Blazer with a 4.3L engine is experiencing severe transmission issues. When connected to a diagnostic scanner, it shows multiple error codes: shift solenoid B malfunction (P0758), oxygen sensor A failure, and oxygen sensor B failure. I took the vehicle to a mechanic who diagnosed the transmission as faulty and replaced it entirely. However, the problem persists. The truck starts in 1st gear, shifts smoothly to 2nd, but then struggles to move into 3rd gear. Once in 3rd, I must manually shift between 2nd and 3rd gears to maintain control. Interestingly, after my dog chewed the wire connected to the speedometer sensor, the truck shifted seamlessly between 1st and 2nd gears—without any issues—but lost 3rd gear entirely. After reconnecting the wiring and re-scanning, it returned to its original shifting behavior. I'm seeking advice on how to properly diagnose this issue. Is P0758 a valid reason for transmission replacement? I understand that P0758 typically indicates a circuit fault—such as faulty wiring or a defective solenoid—and not necessarily a failing transmission unit. A proper pinout test and wiring inspection would be needed to confirm the root cause.