P080D: Upshift/Skip Shift Solenoid Control Circuit High

What does P080D 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. P080D means the control line is shorted to positive: with the low-side driver on, the line should be pulled to ground but reads high (GM: 0.5 Ω or less to the supply). The solenoid cannot be energized and the driver is protected or switched off. GM checks it only with the driver on, 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 in all tables from 2015 to 2019. Without power the solenoid does not lock, so 1 to 2 stays free.

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

Symptoms

• Check engine lamp after two trips
• 1-4 lockout not working
• Otherwise no change in driving

Common causes

• High Control wire shorted to battery voltage (damaged harness)
• Medium Solenoid coil with shorted turns (resistance near zero)
• Medium Substitute resistor ('eliminator') with too low a value
• Low Engine module driver faulty

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