Auto Shift Manual Control Circuit
Diagnostic trouble code P0950 indicates a malfunction in the Auto Shift Manual (ASM) control circuit. 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 control circuit, which manages the upshift and downshift requests in an automated manual or electronically controlled automatic transmission.
While the vehicle can usually still be driven, the manual shifting feature may be disabled, and erratic automatic shifting could occur. It should be diagnosed soon to prevent potential drivability issues or further transmission stress.
Common symptoms
- Check Engine Light illuminated
- Inability to use manual shift mode (paddle shifters or tap-shift)
- Harsh or erratic transmission shifting
- Transmission stuck in a specific gear (limp mode)
- Gear indicator on the dashboard flashing or displaying incorrectly
Likely causes
- Faulty Auto Shift Manual (ASM) switch or shifter assembly
- Damaged, corroded, or loose wiring and connectors in the ASM circuit
- Spilled liquid or debris inside the center console affecting the shifter switch
- Faulty Transmission Control Module (TCM)
- Faulty Powertrain Control Module (PCM)
What to check before replacing parts
Scan for all related diagnostic trouble codes and record freeze frame data.
Look for: Check if there are other transmission or communication codes present that might indicate a broader electrical issue or TCM failure.
Visually inspect the wiring and connectors related to the shifter assembly and ASM circuit.
Look for: Look for chafed wires, loose connections, corrosion, or signs of liquid intrusion (like spilled coffee) near the center console shifter.
Test the Auto Shift Manual switch operation using a digital multimeter or scan tool.
Look for: Verify that the switch state changes correctly on the scan tool data stream when moving the shifter through the manual upshift and downshift positions, or check for proper continuity/resistance at the switch terminals.
Check the voltage and ground circuits at the ASM switch connector.
Look for: Ensure the switch is receiving the correct reference voltage (usually 5V or 12V depending on the system) and has a solid ground. A lack of voltage indicates a wiring issue between the module and the switch.
Perform a continuity test on the signal wire between the ASM switch and the TCM/PCM.
Look for: An open circuit (infinite resistance) or a short to ground/power indicates a wiring harness failure that needs repair.
This page explains the generic P0950 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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