P2780: Downshift Switch Circuit Low

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.

Symptoms

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

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fluid level and condition according to the manufacturer
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Check the transmission connector
4. Read the data with a transmission-compatible scanner
5. Measure the solenoid valve circuit
6. Leave opening the transmission to a specialized repair shop

Good to know

• Repair difficulty: medium

What each character of P2780 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 7: Transmission
• 80: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2780?

Drive as little as possible and gently. If the transmission slips or stays in one gear, go slowly to a repair shop or call for a tow truck.

What causes code P2780?

The most common causes are: signal wire rubbed through or pinched to ground; minus paddle shorted internally.

Related codes

• P2779Downshift Switch Circuit Range/Performance
• P2781Downshift Switch Circuit High
• P2782Downshift Switch Circuit Intermittent/Erratic
• P0816Downshift Switch Circuit
• P2776Upshift Switch Circuit Low

Sources

• gsi.ext.gm.com: 23OBDG07
• gsi.ext.gm.com: 24OBDG07
• fordservicecontent.com: OBDSM2400OUTPUT 16Jul2024 WSM final V2 MCS7001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.