P07B9Transmission Park Position Sensor/Switch B Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- With electronic gear selection the park position sensor/switch reports the park request or position. On GM's shift-by-wire selectors (2017 LaCrosse, XT4/XT5, Bolt EV, later SUVs and pickups) it is the P button, read by two redundant analog sensors A and B with separate 'released' and 'pressed' voltage zones. P07B9 is the same check as P07B3 for sensor B: below 446 counts (43.6 % of 5 V) in GM's selector modules, below 35 % in the ICCM, 115 or less in the 2025 diesel engine module, after two trips. A short to ground or an open supply is typical.
- What you may notice
- Check engine light, 'service transmission' or 'unable to shift' message
- Park cannot be selected by button, or the car will not shift out of P
- P button illumination off
- Likely causes
- LikelySignal shorted to ground or supply wire open
- PossibleSelector knob not fully seated or connector not latched
- PossibleSensor in the P button faulty
- RareSelector or control module
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.