Faulty park position sensor or switch, or selector range sensor assembly, giving a low output; Wiring short to earth or chafed harness on the park position circuit B; Corroded, damaged or water-affected connector at the sensor or control unit; Selector linkage or cable out of adjustment so the switch reads the wrong position; Open circuit or poor reference supply or earth to the sensor; Fault within the transmission or powertrain control unit.

P07B9

Transmission Park Position Sensor/Switch B Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
B9: FaultThe specific fault in that area

What it means

P07B9 is the generic code for a low signal in circuit B of the transmission park position sensor or switch. The transmission or powertrain control unit saw a voltage lower than expected on that circuit, typically a short to earth, an open circuit or a faulty sensor. The control unit can no longer reliably confirm whether the transmission is in Park.

Symptoms

Engine will not crank, or cranks only in certain selector positions
Gear selector position shown incorrectly on the dashboard
Reversing lights or shift interlock not working correctly
Warning light on, possibly with a transmission warning message
Car may not lock or switch off properly, or may roll when it should be held in Park
Harsh, delayed or incorrect gear engagement

Possible causes

Faulty park position sensor or switch, or selector range sensor assembly, giving a low outputlikely
Wiring short to earth or chafed harness on the park position circuit Blikely
Corroded, damaged or water-affected connector at the sensor or control unitpossible
Selector linkage or cable out of adjustment so the switch reads the wrong positionpossible
Open circuit or poor reference supply or earth to the sensorpossible
Fault within the transmission or powertrain control unitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting any other transmission or selector-related codes
Check the live data for park or range sensor status while moving the selector through every position, and compare it with the actual lever position
Visually inspect the sensor, harness and connectors for damage, chafing, oil contamination, corrosion and water ingress
Check the battery condition and charging voltage, as low voltage can cause false circuit faults
Check the selector linkage or cable adjustment and the lever condition, following the manufacturer's procedure for the model
Measure the reference supply, earth and signal voltages at the sensor connector against the manufacturer's specification
Test the harness for short to earth and for continuity between the sensor and control unit with the connectors disconnected
Clear the code and road test to see whether it returns, which helps to confirm the repair

How to fix

Replace the park position sensor or switch, or the range sensor assembly, if it fails testing
Repair or replace the damaged wiring section causing the short to earth
Clean, repair or replace corroded or damaged connectors and seal out moisture
Adjust or repair the selector linkage or cable and recalibrate the sensor if the model requires it
Repair the supply or earth fault on the sensor circuit
Replace or reprogram the control unit only after the wiring and sensor are proven good and the manufacturer confirms it is necessary

Can I keep driving?

Medium severity

The car may be driven carefully if it starts and drives normally, but get it checked soon as it may fail to start or not hold in Park. Always use the handbrake when parking, and do not rely on Park alone.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.