P07B9: Transmission Park Position Sensor/Switch B Circuit Low

What it means

The signal in park position sensor or switch B circuit is below the expected range.

At a glance

• Usually lights the check-engine light

How it works

Park position sensor or switch B sends its signal to the transmission control module on circuit B. P07B9 sets when that signal is below the expected range, pointing to a low signal on the B circuit rather than a high signal or an open circuit.

Common causes

Most likely first.

1. Wire shorted to ground
2. Connector pins corroded - high contact resistance
3. Harness chafing through insulation

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. Capture freeze-frame data and inspect live data for sensor B's signal and the conditions when it falls low.
2. Inspect circuit B from sensor B to the module for chafing, crushed insulation, corrosion, or a pin contacting ground.
3. Check sensor B and module connector terminals for corrosion or weak contact that could pull the signal below its expected range.
4. Use the wiring diagram and manufacturer's procedure to test circuit B for an unintended short to ground.
5. If the wiring and connectors pass, test sensor or switch B and the module input against the manufacturer's specification.

Common fixes

• Clean and secure corroded or loose circuit B connector terminals.
• Repair damaged wiring that shorts circuit B to ground.
• Replace sensor or switch B if its output remains low during the specified test.
• Repair the module input only after testing isolates the fault there.

Can I keep driving?

Use the parking brake and confirm the vehicle is secure when parked, since an incorrect park signal can affect transmission control. Avoid driving if gear indication or shifting becomes unreliable, or if slipping or limp mode occurs.