U3504Control Module Input Power B Circuit Range/Performance
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- U3504 checks the plausibility of the second supply input, B. Modules with high-power stages often split their supply: in GM's electric brake booster tables B is the battery feed of the booster circuit (voltage sensor 1), checked separately against low and high limits and compared with feed C. U3504 applies when B is present but implausible, for example disagreeing with the logic supply or failing to follow battery voltage under load, without crossing a hard limit. No manufacturer documents U3504 publicly. Because B often feeds valves or motors, a high resistance tends to show only while current flows, as a drop that is invisible at rest. Measure the voltage drop across fuse, connector and ground under load and check whether U3018 or U3505 are stored as well.
- What you may notice
- Power stage functions weak or switched off under load
- Code mainly when motors or valves are active
- Likely causes
- PossibleResistance in fuse, connector or ground of feed B under load
- PossibleFeed B supplied from a different source than expected
- RareDrifting measurement of feed B inside the module
- Repair
- Medium · Often possible to do yourself.Typical cost: €10 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.