P0820 — Problem with gear lever position sensor circuit

The code indicates an issue with the sensor that detects the gear lever's position. This sensor tells the car's computer which gear is selected. If it malfunctions or its circuit has a fault, the car may not correctly recognize the gear, causing shifting problems or incorrect gear display.

Common causes

The cause is almost always one of a few things. Here they are — P0820 rarely comes from anything outside this list:

• Faulty gear lever position sensor
• Damaged or corroded wiring/connectors
• Loose or misaligned sensor
• Faulty transmission control module
• Intermittent electrical connection

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Check and clean sensor connectors and wiring
2. Inspect wiring harness for damage or corrosion
3. Test sensor operation and replace if faulty
4. Check transmission control module for faults
5. Replace gear lever position sensor if needed

That is what holds for P0820 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.