What it means
The auto-shift manual mode circuit reports a intermittent condition. Manual mode shift requests cannot be reliably interpreted.
At a glance
- Usually lights the check-engine light
How it works
The automatic transmission uses a manual-mode switch or position sensor to detect upshift and downshift requests. The transmission control module watches for a stable signal as the selector is moved. P0959 sets when that signal drops out or changes unpredictably rather than showing a consistent circuit fault.
Common causes
Most likely first.
- Connector not seated
- Noisy ground reference
- Connector with intermittent contact under vibration
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
- Record freeze-frame data and review live manual-mode input data for dropouts, especially when the fault was recorded.
- Operate the selector through manual mode while watching the data and gently move the harness near the switch and transmission connectors to look for signal interruptions.
- Inspect the switch or sensor connector for incomplete seating, loose terminals, corrosion, or signs of vibration-related movement.
- Check the ground and reference connections used by the manual-mode circuit for looseness or unstable contact.
- If the signal still cuts out, test circuit continuity and terminal retention while moving the harness, following the manufacturer's procedure.
Common fixes
- Reseat and lock the manual-mode circuit connector.
- Clean corroded terminals and repair loose or damaged connector contacts.
- Repair a poor ground or damaged wiring causing the signal to fluctuate.
- Replace a switch or sensor that intermittently loses its output, then confirm stable live data during selector operation.
Can I keep driving?
If shifts remain normal, keep driving limited and avoid depending on manual mode. If the fault causes missed or unpredictable shifts, stop driving until the circuit is repaired because the transmission may suddenly lose the requested gear.
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.