P0855: Drive Switch Input Circuit High
The P0855 code indicates that the Powertrain Control Module (PCM) has detected a voltage signal from the drive switch (also known as the park/neutral position switch or transmission range switch) that is higher than the expected range. This switch tells the PCM whether the transmission is in Park, Neutral, Drive, or Reverse. A high voltage reading typically means there is a short to power in the circuit, a faulty switch, or a problem with the PCM itself. This can affect transmission operation and starting safety.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine may not start or starts only in Park or Neutral
- Transmission may not shift properly or stay in limp mode
- Backup lights may not work or stay on constantly
2. Most Common Causes
- Faulty transmission range sensor (TRS) / gear position switch
- Signal circuit shorted to battery voltage (B+)
- Open signal circuit (broken wire or disconnected connector)
- Corroded, loose, or damaged connector terminals
- Internal PCM failure (rare)
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Visually inspect the drive switch and its wiring for damage, corrosion, or loose connections.
Step 3: Test the drive switch voltage signal with a multimeter; compare to manufacturer specifications.
Step 4: If voltage is high, disconnect the switch and see if voltage drops; if so, replace the switch.
Step 5: Check for shorts to power in the wiring harness; repair as needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The vehicle may not start, or the transmission may shift erratically, leading to unsafe driving conditions.
How much does it cost to fix?▼
Typically between $50 and $150 for parts and labor, depending on the vehicle and whether the switch or wiring needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.