Park/Neutral Switch Input Circuit Malfunction
The P0850 code indicates a problem in the park/neutral position (PNP) switch circuit, which tells the PCM whether the transmission is in Park or Neutral. This switch is critical for starting the engine and engaging safety features. A fault can prevent starting or cause erratic transmission behavior.
1. Symptoms You Will Notice
- Engine cranks but won't start
- Engine starts in gear
- Check Engine Light illuminated
- Transmission shifting issues
2. Most Common Causes
- Faulty or misadjusted park/neutral safety switch
- Open or short circuit in the wiring harness
- Corroded, damaged, or poorly connected electrical connectors
- Faulty CAN bus communication line
- Damaged PCM or TCM (rare)
- Low transmission fluid level or contaminated fluid (on transmissions with internal switch)
3. Step-by-Step Diagnosis
Step 1: Scan for codes and verify P0850 is present.
Step 2: Inspect the PNP switch and its wiring for damage or corrosion.
Step 3: Test the switch continuity with a multimeter in Park and Neutral positions.
Step 4: Check voltage and ground signals at the PCM connector.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The vehicle may not start or could start in gear, posing a safety risk. Have it diagnosed immediately.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on the switch location and labor rates.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.