GM 28 Auto Transmission Range Pressure Switch Error
How to read it
Code 28 reads as 2 flashes, pause, 8 flashes 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 28 mean?
Auto Transmission Range Pressure Switch Error
Common causes of 28
- Failed transmission pressure switch assembly
- Internal transmission fluid leak into the switch connector
- Damaged wiring between the transmission and ECM
- Low fluid or worn valve body causing wrong pressure readings
How to fix 28
- Check fluid level and condition before electrical diagnosis
- Inspect the transmission pass through connector for oil and corrosion
- Test pressure switch continuity in each gear range per the manual
- Repair wiring faults before opening the transmission
- Recheck gear indication on a scan tool after repairs
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 28. Include your vehicle, the issue and a source if you have one.