What it means
Voltage on the downshift switch line is above the expected window. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The downshift switch circuit carries the driver's request for a lower gear to the transmission control module. This code sets when the monitored signal is above the expected range, which can result from open switch contacts, a short to battery voltage, or a poor connector connection.
Common causes
Most likely first.
- Open switch contacts
- Switch wire shorted to B+
- Connector pins corroded - high contact resistance
Symptoms
- Check engine or transmission warning light may be on
- Downshift switch may not respond or may register unexpectedly
- Manual shift mode may behave unpredictably
How to diagnose it
- Read freeze-frame data and monitor downshift-switch voltage or status with the switch released and pressed to confirm the signal remains high.
- Inspect the switch connector for open, corroded, loose, or pushed-back terminals and check whether the switch contacts close when operated.
- Inspect the circuit for an open wire or a short to battery voltage, paying attention to chafing and previous repairs.
- Test switch continuity and circuit voltage using the manufacturer's procedure to separate failed contacts from a harness fault.
- If the switch and wiring pass, compare the signal at the control-module connector with the switch-end reading and verify module grounds.
Common fixes
- Restore a loose or corroded connector connection at the switch.
- Repair an open or damaged wire in the downshift switch circuit.
- Repair wiring shorted to battery voltage.
- Replace the downshift switch if its contacts remain open when operated.
- Repair a control-module connection or replace the module only if circuit tests point to it.
Can I keep driving?
If the transmission shifts normally, drive cautiously to arrange diagnosis and avoid relying on the downshift switch or manual mode. Unexpected or unavailable downshifts can reduce control during hills or overtaking.
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.