P080C: Upshift/Skip Shift Solenoid Control Circuit Low

What does P080C mean?

GM's skip-shift (CAGS) on manual gearboxes such as the T56 and TR6060 uses an engine-module solenoid that, at light load, blocks the way from 1st into 2nd so the driver shifts 1 to 4; the 1-4 lamp shows it (P0804). The engine module drives the solenoid with a low-side driver; P0803 is the open circuit. P080C means the control line is shorted to ground: with the driver off it should sit at battery voltage through the coil but reads low (GM: 0.5 Ω or less to ground). GM checks it from 9 V (2015/16: 11–32 V) and above 250 rpm, 5 of 6 samples of 250 ms, type B with the MIL after two trips; the 2019 LT5 uses 20 of 25 samples and type A, one trip. In the 2015/16 tables P080C also covers an open circuit. A low-side short keeps the solenoid energized, so the lockout may stay active.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine lamp
• 1-4 lockout permanently active or not working
• 1-4 lamp possibly unrelated to the lockout

Common causes

• High Control wire chafed through to ground at gearbox or frame
• Medium Solenoid coil shorted to its housing
• Medium Connector corroded or water ingress
• Medium Older GM modules: circuit open or solenoid unplugged
• Low Engine module driver faulty

Likelihood is a general estimate across vehicles; your make and model may differ.