What it means
General electrical fault on the third transmission mode select switch input C — used for additional drive modes (Sport, Snow, Tow/Haul, Eco) on transmissions that offer more than two operator-selectable shift maps. Without a valid input the TCM falls back to the default mode.
At a glance
- Usually lights the check-engine light
How it works
Transmission mode switch input C reports a selected shift mode to the TCM on vehicles equipped with this additional mode input. The TCM sets this circuit code when the input voltage or state is electrically invalid, and may use its default shift mode instead.
Common causes
Most likely first.
- Faulty transmission mode switch or selector
- Open or shorted switch wiring
- Loose, damaged, or corroded connector
- Fault in the transmission control module input circuit
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Save freeze-frame data and check scan-tool mode-switch data to see whether input C changes when the driver selects the associated transmission mode.
- Inspect the mode selector and its connector for damage, loose fit, or contamination.
- Check the wiring between the selector and TCM for opens, shorts, or corroded terminals.
- Test the switch input and circuit states against the manufacturer's wiring diagram and specification.
- If the switch and wiring pass, check the TCM input circuit using the manufacturer's procedure.
Common fixes
- Repair or replace a damaged transmission mode switch or selector.
- Reconnect or clean corroded input C terminals.
- Repair open or shorted wiring in the mode switch circuit.
- Repair a confirmed TCM input fault after ruling out the switch and wiring.
Can I keep driving?
The transmission may default to another shift mode, so avoid relying on the selected mode and drive gently until repaired. If shifting becomes harsh, slips, or gears are lost, stop driving and have the fault checked.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.