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DTC codes / P07xx · Transmission / P07B8

P07B8Transmission Park Position Sensor/Switch B Circuit/Open

P07B8 indicates that the transmission control module has detected an open circuit or abnormal voltage on the signal circuit for Park Position Sensor/Switch B, which is used to confirm the transmission is mechanically locked in Park. The computer compares expected voltage on the sensor's signal line against what it actually sees and flags the code when the circuit is open or the signal is missing.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The warning light (malfunction indicator lamp) illuminates on the dashboard.
  • The engine may not start because the computer does not receive a confirmed Park signal.
  • The gear selector may feel loose or fail to engage Park fully.
  • A message such as 'Shift to Park' or 'Transmission not in Park' may appear on the driver information display.
  • The vehicle may not allow the key to be removed or the shifter to move out of Park.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. A damaged or corroded Park Position Sensor/Switch B or its electrical connector.
  2. An open or chafed wire in the sensor's signal or ground circuit.
  3. A faulty transmission control module (TCM) or a poor connection at the TCM harness.
  4. Mechanical wear or misalignment inside the transmission range selector mechanism.
  5. Water intrusion or debris contamination at the sensor or connector.
  6. A blown fuse or relay that supplies power to the sensor circuit.

How to diagnose and fix it

  1. Connect a scan tool and record all stored and pending codes, then clear the code and test-drive to see if it returns.
  2. Visually inspect the Park Position Sensor/Switch B, its connector, and the wiring harness for damage, corrosion, or loose pins.
  3. Check the sensor's power, ground, and signal circuits with a digital multimeter to confirm an open or short.
  4. Perform a wiggle test on the harness and connector while watching live data for the Park signal to catch intermittent faults.
  5. If the circuit tests good, remove and bench-test the sensor or replace it with a known-good unit.
  6. Check the transmission range selector mechanism for mechanical binding or misalignment that could prevent the sensor from signaling Park.
  7. If all external circuits and the sensor are good, inspect the TCM connector and, if necessary, test or replace the TCM.

Before you replace the park sensor

  • A loose or corroded connector at the sensor is far more common than a failed sensor itself, so always inspect and clean the terminals before condemning the part.
  • The code can be set by a weak or dying battery because low voltage during cranking can momentarily drop the sensor signal below the threshold the TCM expects.
  • On some vehicles, the Park Position Sensor B is integrated into the transmission range switch, so replacing only the external sensor may not fix the fault if the internal switch is worn.
  • An intermittent open circuit that only appears when the engine is hot or after driving over bumps often points to a chafed wire hidden inside the loom, not the sensor.
  • Do not assume the TCM is faulty just because the code persists after sensor replacement; a poor ground at the transmission case can mimic an open signal circuit.

Can I keep driving with P07B8?

If the vehicle starts and drives normally, you can drive it to a repair shop, but avoid relying on the Park position for safety until the fault is fixed. If the engine will not start or the shifter will not move out of Park, do not force it; have the vehicle towed or repaired on site.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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