What Does P07B9 Mean?
The transmission park position sensor/switch "B" circuit is reading lower voltage than expected. The TCM has detected that sensor B's signal is below the normal operating range for the current transmission position. This indicates a potential short to ground in the wiring, a failed sensor with low internal resistance, or connector issues creating a ground path. Since sensor B serves as a redundant Park position verification, this fault reduces the system's ability to reliably confirm Park engagement.
Common Causes
35%
Short to ground in park position sensor B signal wire from chafed insulation
30%
Failed park position sensor B with internal short producing low voltage output
20%
Moisture intrusion or corrosion in sensor B connector creating a ground path
10%
Internal transmission harness damage near sensor B location
5%
TCM ground reference issue affecting sensor B signal interpretation
Diagnostic Steps
1
Measure park position sensor B signal voltage at the TCM connector with the transmission in Park and compare to factory specifications.
2
Disconnect sensor B and verify the signal voltage at the TCM rises to reference voltage, confirming a sensor or wire-side short to ground.
3
Inspect sensor B wiring for chafed insulation, pinched wires, or contact with metal components that could create a ground short.
4
Test sensor B resistance values through all gear positions and compare to manufacturer specifications.
5
Check the sensor B connector for moisture, corrosion, or contamination that could create a low-resistance path to ground.
Estimated Repair Cost
$120 - $550
Parts + labor, varies by vehicle and location
The transmission park position sensor/switch "B" circuit is reading lower voltage than expected. The TCM has detected that sensor B's signal is below the normal operating range for the current transmission position. This indicates a potential short to ground in the wiring, a failed sensor with low i...
The most common cause of P07B9 (Transmission Park Position Sensor/Switch "B" Circuit Low) is: Short to ground in park position sensor B signal wire from chafed insulation
Typical repair costs for P07B9 range from $120 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle may still operate using sensor A for Park detection, but the redundancy is compromised. Gear position display may be inaccurate, and the system may intermittently fail to recognize Park position. Always use the parking brake. Schedule repair soon.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P07B9 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Control / Park System
Difficulty
Type
Generic (SAE)
Recommended Tools
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