Error Code P07B9 is defined as Transmission Park Position Sensor/Switch B Circuit Low. meaning it applies to all vehicles with the OBD-II system, particularly those made from 1996 onwards and equipped with automatic transmission. Specifications on the definition and steps for repairs may vary depending on the model and make of the vehicle.

This includes vehicles from, but not limited to, Chevrolet, Dodge, Ford, Land Rover, Toyota, and Volkswagen. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.

This code indicates that the PCM (control module, also known as ECM or engine control module in other vehicle makes) has detected a malfunction that affects the operation of the transmission park position sensor/switch “B.”

The job of the transmission park position sensor/switch “B” is to observe the status of the transmission. When the transmission is in the park position, the circuit sends signals to the PCM. Based on the specific vehicle, this is a safety feature to keep the starter from engaging with the automatic transmission in gear.

With that said, it is associated with several Transmission Park Position Sensor/Switch “B” Circuit codes, namely:

  • Error Code P07B8
  • Error Code P07BA
  • Error Code P07BB
  • Error Code P07BC
  • Error Code P07BD

The specific situation determines the code that the PCM activates. When the Error Code P07B3 appears, that means that there is a low output voltage detected in the transmission park position sensor/switch “A” circuit.

Common Symptoms

  • No start (starter will not engage)
  • Starter engages when the vehicle is in gear
  • Transmission may not shift out of park position
  • Transmission may not shift into the park position
  • Check Engine light is on

Possible Causes

  • Faulty Transmission Park Position Sensor/Switch
  • Faulty connector (corroded or damaged)
  • Faulty wiring
  • Defective PCM (rare)

How to Check

As with most error code problems, the first step to troubleshoot this code is to check with the Technical Service Bulletin (TSB) for the common issues with the vehicle.

Next, find all the components associated with the transmission park position sensor/switch “A” circuit. This includes the transmission park sensor/switch itself, connectors, wiring, and PCM. Depending on the make, model, and year of the vehicle, the components may come with more components. Check all these components thoroughly. Make sure there are no visible problems with the wires (bare, burn, scraped, etc.). Also, make sure you check the connectors. Look for signs of corrosion buildup or damaged pins.

Advanced Steps

This is usually vehicle specific and may require special tools and equipment to perform, such as digital multimeter and the vehicle’s specific technical references. Also, voltage requirements may vary based on the make, model, and specific year of the vehicle.

Circuit Checks

As said earlier, voltage requirements can vary on the specific vehicle, as well as the transmission park position sensor/switch circuit configuration and other components. Thus, you should check it with the technical data. Find the right voltage specifications and follow the specific troubleshooting sequence. Internal failure usually happens when the right voltage input to a sensor/switch without the voltage output.

If the troubleshooting showed the absence of a power source or ground, then conduct a continuity test to check the condition of the connectors and wirings. A continuity test is performed with the power removed from the circuit. The normal reading must be at 0 ohms of resistance unless otherwise specified in the technical data.

Resistance or no continuity means there is a problem with the connectors or wirings, or there is an open or short in the wiring. Replace or repair as necessary.

How to Fix

Common repairs for this code include:

  • Replacement of the transmission park position sensor/switch
  • Repair or replacement of defective wiring or connectors
  • Cleaning corrosion off of the connectors
  • Replacement or flashing of PCM

The severity of this error code usually depends on the specific malfunction and the level of progress. However, this problem could become a safety issue, since the starter will engage with the vehicle in gear. Thus, to prevent its progress, it is vital to address it as soon as possible.