What causes GM code 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 do I fix GM code 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

28 Auto Transmission Range Pressure Switch Error

Q: What does GM code 28 mean?

GM code 28. Auto Transmission Range Pressure Switch Error. Applies to 1988-1995 GM cars and trucks with automatic transmission, Corvette, C/K trucks.

Make: GM (1982-1995)
Category: Powertrain - Transmission
Severity: Check Engine Light
Applies to: 1988-1995 GM cars and trucks with automatic transmission, Corvette, C/K trucks

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.

What does GM code 28 mean?

28. Auto Transmission Range Pressure Switch Error. This code sets when your vehicle computer detects 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