Network, generic (extended)

U3504 Control Module Input Power B Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Resistance in fuse, connector or ground of feed B under load
Feed B supplied from a different source than expected
Drifting measurement of feed B inside the module

Symptoms

  • Power stage functions weak or switched off under load
  • Code mainly when motors or valves are active

Repair estimate

DifficultyMediumDIY possible
Parts and labour€10–500
Time0.3–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

module power bpower wiring

Related codes

U3505U3506U3507U3007U3018

References: law.cornell.edu, gsi.ext.gm.com.