🚨 Diagnostic Profile
- Vehicle/Equipment Make: GENERIC
- Technical Description: Brake Booster Motor A Phase U-V-W Circuit/Open
This code is set by the Electronic Brake Control Module (EBCM) when it detects an open or high-resistance condition on one or more of the three-phase (U, V, W) windings that drive the electric brake booster pump motor. Many modern brake-by-wire and electro-hydraulic brake booster assemblies use a brushless DC motor to generate hydraulic pressure for brake assist instead of a traditional vacuum booster. The EBCM monitors current flow and feedback across these three phase windings to confirm the motor is spinning correctly and producing adequate pressure. If any one of the U, V, or W phase circuits reports an open circuit, a broken winding, a disconnected pump motor connector, or a wiring harness break between the EBCM and the booster pump assembly, this code will set. This typically triggers a stability control warning light, a brake system warning indicator, and in many cases a noticeably harder brake pedal due to loss of power assist, since the pump can no longer build or maintain hydraulic pressure.
🚨 Repair Difficulty Tier
- Difficulty Rating: Professional Only
This repair requires a bidirectional scan tool capable of reading EBCM-specific live data and running booster pump actuation tests, along with a digital multimeter to check resistance and continuity across three separate phase windings. Because this system is tied directly to brake assist and hydraulic pressure generation, any wiring or component work carries significant safety liability and should only be performed by a technician trained in electro-hydraulic brake systems.
🛠️ Resolution Steps
- Step 1: Preliminary Inspection
Begin by visually inspecting the brake booster pump motor connector and surrounding wiring harness for corrosion, melted insulation, chafing, or a loose/disconnected pin. Check the connector at the EBCM as well, since a pushed-out terminal or damaged pin on either end can create an open circuit on one of the phase lines. - Step 2: Diagnostic Verification
Using a digital multimeter, back-probe the U, V, and W terminals at the brake booster pump motor connector and measure resistance phase-to-phase; all three readings should be nearly identical per the manufacturer’s specification, and any phase reading infinite resistance confirms an open winding or broken wire. With a scan tool, access EBCM live data and attempt a brake booster pump motor actuation test to see if the pump engages and if the module reports a stored fault on a specific phase. - Step 3: Resolution & Reset Process
If resistance testing confirms an open winding inside the pump motor itself, the brake booster/hydraulic pump assembly must be replaced as a unit, as these motors are not individually serviceable. If the fault is isolated to the harness or connector, repair or replace the damaged wiring section and connector terminals. After repair, bleed the brake hydraulic system per manufacturer procedure, clear the stored code with a scan tool, and perform a booster pump relearn or initialization procedure if required by the vehicle platform.
📦 Parts, Labor, and Budget Estimates
- Required Components/Software: Brake booster/hydraulic pump motor assembly, wiring harness repair kit or connector terminals, bidirectional scan tool with EBCM actuation capability, digital multimeter
- Average Component Price: $250 – $650 USD (pump assembly varies widely by make/model)
- Estimated Labor Hours: 1.5 – 3.0 hours (includes diagnosis, replacement, and brake system bleeding)
- Total Estimated Budget: $400 – $950 USD