Powertrain, generic · Transmission
P07B9 Transmission Park Position Sensor/Switch B Circuit Low
Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible
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.
Likely causes
Signal shorted to ground or supply wire open
Selector knob not fully seated or connector not latched
Sensor in the P button faulty
Selector or control module
Symptoms
- 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
Repair estimate
DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
park position sensorelectronic range selectorsensor wiringtransmission control module
Related codes
References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.