P0955: Auto Shift Manual Mode Circuit

What it means

The auto-shift manual mode circuit reports a fault condition. Manual mode shift requests cannot be reliably interpreted.

At a glance

• Usually lights the check-engine light

How it works

The auto-shift manual mode circuit tells the control module when the driver selects manual shifting. P0955 sets when the module detects a general fault in that mode circuit and cannot reliably accept manual shift requests; a failed mode switch or wiring fault can interrupt the signal.

Common causes

Most likely first.

1. Mode switch failed
2. Wiring fault

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

1. Record freeze-frame data and check live data for the manual mode selection and shift request inputs as the control is operated.
2. Inspect the mode switch and its connector for damage, loose fit, corrosion, or contamination.
3. Check the manual mode circuit wiring and grounds for an open, short, or poor connection.
4. Measure the switch output while changing modes and compare its operation with the manufacturer's specification.
5. If the switch and wiring test correctly, check the module input and related circuit connections using vehicle service information.

Common fixes

• Reseat or clean the manual mode switch connector.
• Repair damaged wiring or a poor ground in the mode circuit.
• Replace a failed manual mode switch.
• Repair a confirmed module input fault.

Can I keep driving?

The transmission may continue to shift automatically, but manual mode or its shift requests may not work. Drive without relying on manual selection, and stop if shifting becomes harsh, slips, or the vehicle enters limp mode.