GM 31 Gear Position Switch Circuit Error
How to read it
Code 31 reads as 3 flashes, pause, 1 flash on the check-engine light. Jump terminals A and B on the ALDL connector with the key off, then turn the key on with the engine off and count the check-engine flashes.
New to flash codes? The How to Read GM OBD-I Codes with a Paperclip walks through the test and what the numbers mean. The general OBD-I guide covers the rest.
What does GM code 31 mean?
Gear Position Switch Circuit Error
Common causes of 31
- Misadjusted park neutral position switch
- Corroded PRNDL switch contacts
- Damaged wiring between the switch and ECM
- On turbo models a wastegate solenoid fault uses this same code
How to fix 31
- Verify the engine cranks only in park and neutral
- Inspect and adjust the position switch per the service manual
- Test switch continuity in each gear position
- Clean or replace corroded connectors before replacing the switch
- On turbo 3.8L models test the wastegate solenoid as the alternate cause
Source
Qualified source review
Sources and review
Review: qualified. Read the source limits below.
- GM and Chevrolet OBD1 Trouble Codes (ALDL Fault Code List)
live reference page (troublecodes.net)
Supports: code identity and GM meaning
Fetched directly. Single publisher, so the record is qualified, not verified. Causes and check order are curator-written from the circuit the code names.
https://www.troublecodes.net/gm/
Last updated 2026-09-19.
Report a correction for 31. Include your vehicle, the issue and a source if you have one.