Torque converter not commanded to lock.

[Cbutler454]

1997 K2500 454 4L80

I am not getting TC lockup in any gear. When connected to truck with scan tool it doesn't show TC lockup as command "on". Always "off". Have checked brake switch reading in transmission section on scan tool and switch goes from closed to open when pedal is depressed. Engine and trans both show to be getting up to temp via scan tool. What other inputs does the ECU use to determine the TC to lockup?

(Pic of problem child attached for attention)

 

[Schurkey]

When that was MY '97 K2500 7.4L, the problem was engine misfire. The computer disables the converter clutch when it detects misfire.

My #8 cylinder was dead when I bought the truck. Turned out to be an easy fix--the #8 spark plug had a cracked porcelain. One (used!) spark plug fixed both the engine and the transmission.

Verify your misfire counts using a scan tool.

 

[Cbutler454]

Thanks for the info. I have checked with my scan tool and have no missfires. Also note that my “TCC Disabled” reading in the ECU shows it’s not disabled.

TCC solenoid dirty cycle never changes from 0. So something is not telling it to lock torque converter.