🚨 Diagnostic Profile
- Vehicle/Equipment Make: GENERIC
- Technical Description: Brake Booster Motor B Phase U-V-W Current Low
This code is a Chassis diagnostic trouble code set by the Electronic Brake Control Module (EBCM) or the dedicated Brake Booster/Power Steering Control Module. It indicates that the module has detected abnormally low current flow in Phase B of the three-phase (U-V-W) brushless motor windings used to drive the electro-hydraulic or electric vacuum brake booster pump assembly. This motor is responsible for generating the assist pressure needed for brake pedal feel and stopping power on vehicles equipped with electric brake boosters (common on hybrid, stop-start, and advanced ADAS-equipped platforms). A low current reading on one phase of the three-phase winding set typically points to an internal winding fault, a disconnected or corroded phase wire, a failing motor driver transistor inside the pump control module, or insufficient voltage supply to the pump motor. Because this circuit directly affects brake assist, the stability control and traction control systems may also set related faults or disable themselves as a protective measure, and the brake assist indicator on the dash may illuminate.
🚨 Repair Difficulty Tier
- Difficulty Rating: Professional Only
This repair requires a bidirectional scan tool capable of accessing chassis/brake modules, an oscilloscope or advanced digital multimeter to evaluate three-phase motor current waveforms, and specialized knowledge of brake booster pump assemblies. Due to the safety-critical nature of the brake booster system and the need for precise bleeding and calibration procedures after repair, this is not a recommended DIY task.
🛠️ Resolution Steps
- Step 1: Preliminary Inspection
Begin by visually inspecting the wiring harness and connector leading to the brake booster pump motor assembly, checking specifically the Phase B (V-phase) wire for corrosion, chafing, or a loose/disconnected pin. Inspect the pump motor housing for signs of fluid intrusion, overheating, or physical damage, and confirm the main power and ground connections to the EBCM/booster control module are clean and tight. - Step 2: Diagnostic Verification
Connect a scan tool to pull freeze frame data and confirm whether the fault is present continuously or intermittently. Using a digital multimeter or oscilloscope, measure resistance and current draw across all three motor phases (U, V, W) to identify imbalance — Phase B should show comparable resistance and current draw to Phases A and C. Command the booster pump motor on using bidirectional controls (if supported) and observe live current data to confirm the fault reoccurs under load. - Step 3: Resolution & Reset Process
If wiring or connector damage is found, repair or replace the affected harness section. If the phase imbalance persists after confirming wiring integrity, replace the brake booster pump motor assembly or the integrated EBCM/booster control module, depending on vehicle architecture. After replacement, clear codes, perform the manufacturer-required brake system bleed and booster initialization/calibration procedure, and road test to confirm proper pedal feel and that no stability or traction control warnings return.
📦 Parts, Labor, and Budget Estimates
- Required Components/Software: Brake booster pump motor assembly, wiring harness repair kit (if applicable), OEM-level scan tool with bidirectional brake module access
- Average Component Price: $350 – $900 USD
- Estimated Labor Hours: 2.0 – 4.0 hours (includes diagnosis, replacement, and brake bleed/calibration)
- Total Estimated Budget: $550 – $1,400 USD