U3028Control Module A Disable Feedback Circuit
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- A disable line is only useful if someone can prove it works, so many designs read back what actually arrives at the switched module. U3028 reports a fault in that feedback path for module A: the returned signal is missing or does not match the state that was commanded. GM's patent US9122662B2 shows the principle: while the ignition is off, several processors set their outputs in a fixed series of test states and compare the resulting output of the inhibit path with the expected value, flagging a fault on any mismatch. FCA's patent US10676100B2 likewise steps through six combinations of shutoff signals. No manufacturer documents U3028 publicly. Unlike U3025, the shutdown line itself may be fine; the system just cannot confirm it, so it often withholds the function until a test passes.
- What you may notice
- Function of module A blocked after the self-test, system warning
- Fault may appear only at start-up or shutdown
- Likely causes
- LikelyOpen feedback wire or loose pin between module A and the monitoring module
- PossibleSelf-test disturbed by low voltage or an early shutdown
- RareFaulty readback stage in module A or the monitoring module
- Repair
- Hard · Usually a job for a workshop.Typical cost: €50 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.