Powertrain, generic (extended)

P2779 Downshift Switch Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2779 is the plausibility fault of the downshift paddle or tip switch. GM's 2023 and 2024 TCM tables for the twin-clutch gearbox define two voltage windows for the minus paddle: 2.2–3.52 V when pulled and 3.826–4.744 V at rest. A reading caught between or around these windows for 120 s is treated as invalid and logged as Type C, no MIL. The same tables use P0816 for a minus paddle held too long. Ford's TR9070 entry in the 2024 OBD summary calls P2779 an illegal voltage on the downshift paddle input. Because the value is still inside the electrical range, suspects are a corroded contact, a drifting resistor in the switch or added resistance in the clock spring rather than a plain short. Paddle downshifts are usually locked out.

Likely causes

Corroded contacts or drifting coding resistor in the minus paddle
Added resistance in the clock spring
Corrosion in the steering wheel connector

Symptoms

  • Downshift paddle inoperative
  • Manual mode refused, usually no MIL

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 switchsteering wheel controls

Related codes

P2780P2781P2782P0816P2775

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