P2779
Downshift Switch Circuit Range/Performance
Transmission controls
Generic OBD-II
Low
What it means
P2779 means the transmission controller sees an implausible or out-of-range signal from the manual downshift switch — the control used in tap-shift, paddle, or tow/haul modes to request a lower gear. The automatic transmission usually keeps shifting normally; the fault is with the driver-request input, most often a bad switch or its wiring.
Low
Can I keep driving? Yes — the automatic transmission still shifts on its own; only the manual downshift request from the switch is unreliable.
Common symptoms
What you'll notice
- Check-engine light on
- Manual/tap-shift downshift requests are ignored or act erratically
- Tow/haul or manual mode may not respond as expected
- No change to normal automatic shifting in most cases
Common causes
Most likely first
- Faulty downshift (paddle/tap-shift) switchLikely
- Liquid spilled into the shifter or switch assemblyCommon
- Chafed, corroded, or loose wiring/connector at the switchCommon
- Poor ground or open in the switch signal circuitLess often
- Transmission control module input fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the code is for the downshift switch input.
- Inspect the switch and connector for spilled liquid, corrosion, or bent pins.
- Operate the switch while watching live data to see if the signal responds.
- Check the wiring and ground between the switch and the TCM for opens/shorts.
- Replace the downshift switch if it fails to signal correctly, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2779?+
Generally yes. The transmission still shifts automatically; you mainly lose reliable manual downshift control. Get it fixed to restore full function.
Can I just clear P2779?+
You can, but it returns whenever the switch or its wiring acts up again until the fault is repaired.
Related codes
Often seen with P2779
Read & clear P2779 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX