Powertrain, generic (extended)

P2780 Downshift Switch Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2780 tells you the downshift switch voltage has fallen under its lower limit. GM's twin-clutch TCM (tables 23OBDG07 and 24OBDG07) checks the TAPDN input against 2.519 V; if the signal stays under that mark for 150 ms while the supply is inside 8.75–18 V and the starter is not engaged, P2780 is logged as Type C, no MIL. In Ford's TR9070 listing from July 2024, P2780 is the out-of-window-low entry for the downshift paddle. A minus-paddle signal pulled toward ground usually comes from a wire rubbed through near the steering column, a pinched harness behind the wheel trim or an internal short in the switch. P2781 is the high-side failure, P2779 the implausible value within range. Manual downshifts are lost; automatic operation carries on.

Likely causes

Signal wire rubbed through or pinched to ground
Minus paddle shorted internally

Symptoms

  • Downshift paddle has no effect
  • Manual mode not available, normally no check engine light

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

downshift switchwiring harness

Related codes

P2779P2781P2782P0816P2776

References: gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com.