U3504 code meaning
Control Module Input Power B Circuit Range/Performance
What U3504 means
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.
U3504 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.3 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3504
- Power stage functions weak or switched off under load
- Code mainly when motors or valves are active
Common causes of U3504
- PossibleResistance in fuse, connector or ground of feed B under load
- PossibleFeed B supplied from a different source than expected
- Less likelyDrifting measurement of feed B inside the module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Module power bPower wiring
What each part of U3504 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 04 | The exact fault in that area. |
What to do next
- Note U3504 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U3504
What does U3504 mean?
U3504 means "Control Module Input Power B Circuit Range/Performance". U3504 checks the plausibility of the second supply input, B. It is a generic code, so it means the same on every make.
Is it safe to drive with U3504?
Drive gently and only to a workshop. With U3504 the car can go into limp mode (reduced power) to protect itself.
Will U3504 fail an emissions test?
U3504 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U3504 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U3504 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.