Auto Shift Manual Mode Circuit
Diagnostic trouble code P0955 indicates a malfunction in the auto shift manual mode circuit, which allows the driver to manually select gears in an automatic transmission. The powertrain control module (PCM) or transmission control module (TCM) sets this code when it detects an improper voltage or resistance signal from the manual shift circuit.
While the vehicle can usually still be driven in fully automatic mode, the manual shifting feature will be disabled. It should be diagnosed soon to restore full functionality and prevent potential wiring issues from affecting other systems.
Common symptoms
- Illuminated Check Engine Light
- Inability to manually shift gears using the shifter or steering wheel paddles
- Transmission remains in fully automatic mode
- Gear indicator on the dashboard may flash or display incorrectly
- Transmission may default to a limp mode in rare cases
Likely causes
- Faulty auto shift manual mode switch (shifter assembly or paddle shifters)
- Damaged, corroded, or loose wiring and connectors in the manual shift circuit
- Spilled liquid on the center console affecting the shifter electronics
- Faulty transmission control module (TCM)
- Faulty powertrain control module (PCM)
What to check before replacing parts
Scan for all present DTCs and record freeze frame data.
Look for: Check if other transmission or communication codes are present, which could indicate a broader electrical issue or module failure.
Visually inspect the wiring and connectors related to the shifter assembly and manual shift circuit.
Look for: Look for frayed wires, loose connections, corrosion, or signs of liquid intrusion (especially near the center console shifter).
Test the auto shift manual mode switch for proper operation using a multimeter.
Look for: Verify that the switch opens and closes correctly and provides the manufacturer-specified resistance or voltage when toggled.
Check the circuit for continuity and shorts between the shifter switch and the TCM/PCM.
Look for: Ensure there is no open circuit, high resistance, or short to ground/power in the wiring harness.
Monitor the manual shift switch PID using an advanced scan tool while operating the shifter.
Look for: Observe if the TCM/PCM recognizes the switch state changes (e.g., upshift/downshift requests). If the switch tests good but the module doesn't see the input, suspect a wiring or module issue.
This page explains the generic P0955 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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