P0855
UniversalDrive Switch Input Circuit High
Medium SeverityThe P0855 code indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected a high voltage reading in the drive switch input circuit. This typically means the module is receiving an incorrect signal regarding the transmission's drive selection, potentially leading to erratic shifting or the vehicle entering limp mode.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical repairs to prevent accidental short circuits or injury. Ensure the vehicle is securely supported if working underneath it, especially when dealing with transmission components. Allow the engine and transmission to cool down before inspection.
Common Symptoms
- Check Engine Light illuminated
- Transmission shifting erratically or harshly
- Vehicle stuck in limp mode (limited gear selection)
- Inability to select drive gear
- Vehicle may not move from a stop
Common Causes
- Faulty drive switch or transmission range sensor
- Open circuit or short to voltage in the wiring harness connected to the drive switch
- Corroded, damaged, or loose electrical connectors
- Internal fault within the Powertrain Control Module (PCM) or Transmission Control Module (TCM) (rare)
Frequently reported on: All Makes
Diagnostic Steps
- Scan for additional Diagnostic Trouble Codes (DTCs) to identify any related issues that might provide more diagnostic clues.
- Visually inspect the wiring harness and connectors for the drive switch (often part of the transmission range sensor) for any signs of damage, fraying, corrosion, or loose connections.
- Using a digital multimeter, test the continuity and voltage at the drive switch input circuit according to your vehicle's specific service manual wiring diagrams. Look for an abnormally high voltage reading when it should be low or vice-versa, depending on the switch's design.
- If the drive switch itself tests faulty (e.g., incorrect resistance or no continuity when actuated), proceed with replacing the drive switch or transmission range sensor.
- After any repairs, clear the code using an OBD-II scanner and test drive the vehicle to confirm the repair and ensure the code does not return.
👨🔧 When to Call a Professional
If you lack experience with electrical diagnostics, do not have access to a multimeter, or if the transmission's behavior is severely unpredictable, it is best to consult a professional mechanic for accurate diagnosis and repair. Incorrect electrical work can cause further damage.
Commonly Asked Questions
What does a 'Drive Switch Input Circuit High' mean?
It means the vehicle's computer (PCM/TCM) is receiving an unexpectedly high voltage signal from the circuit that monitors whether the transmission is in a drive gear, indicating a potential electrical fault in the switch or wiring.
Can I still drive my car with a P0855 code?
While you might be able to drive, it is not recommended for extended periods. This code can lead to unpredictable transmission behavior, including harsh shifts or the vehicle entering limp mode, which can be unsafe and potentially cause further damage.
Is the drive switch the same as a transmission range sensor?
Often, the function of detecting the 'drive' position is integrated into the transmission range sensor (also known as a neutral safety switch). This sensor tells the computer what gear is selected, including drive.
What tools do I need to diagnose P0855?
You will typically need an OBD-II scanner to read and clear codes, a digital multimeter to test voltage and continuity in the circuit, and potentially vehicle-specific wiring diagrams.
Could a P0855 code indicate a transmission problem?
The code itself points to an electrical issue with the switch circuit rather than a mechanical transmission failure. However, an incorrect signal from this circuit can cause the transmission to operate incorrectly, leading to perceived transmission problems like erratic shifting.