Powertrain, generic (extended)

P2781 Downshift Switch Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2781 sets when the downshift switch input climbs above its upper voltage limit. GM's 2023 dual-clutch TCM tables cap the TAPDN signal at 4.774 V; staying above it for 150 ms produces a Type C entry, no MIL. Ford's TR9070 table in the 2024 summary uses P2781 for the out-of-window-high case of the downshift paddle. GM has a field case: Service Update N212350930 (February 2024) covers about 23,500 Chevrolet Corvettes of model year 2021 whose TCM wrongly reported P2781 as permanent, which could fail an inspection that reads permanent codes; the fix is new TCM software. Real faults are mostly an open signal or ground wire or a loose plug at the wheel. P2780 is the low-side twin, P2779 the in-range plausibility fault.

Likely causes

Open signal or ground circuit, loose connector at the wheel
TCM software reporting a false permanent code (2021 Corvette, N212350930)
Broken track in the clock spring

Symptoms

  • Downshift paddle not working
  • Permanent code shown at an emissions inspection although the paddle works (software case)

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–500
Time0.2–2 h

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

Parts involved

downshift switchwiring harness

Related codes

P2779P2780P2782P0816P2777

References: gsi.ext.gm.com, fordservicecontent.com, static.nhtsa.gov.