🚨 Diagnostic Profile
- Vehicle/Equipment Make: GENERIC
- Technical Description: Brake Booster Motor A Position Sensor Supply Circuit High
This chassis code is set by the Electronic Brake Control Module (EBCM) when it detects a voltage reading that is higher than the expected calibrated range on the reference supply circuit feeding the Brake Booster Motor’s Position Sensor (Sensor ‘A’). Modern electric brake booster units rely on an internal electric motor and position sensor to precisely modulate brake pedal feel and assist pressure, replacing traditional vacuum-based systems. The EBCM continuously monitors the supply voltage to this sensor to ensure it stays within a tight tolerance (usually between 4.5V and 5.5V for a standard 5V reference circuit). A ‘Circuit High’ fault indicates that the sensor is receiving a voltage higher than this programmed threshold, which is typically caused by a short-to-power (B+) condition in the wiring harness, a faulty internal sensor, or a problem within the EBCM driver itself. Because this sensor is integral to the brake assist motor’s positioning, the module may default to a reduced-assist safety mode, resulting in a harder-than-normal brake pedal and the illumination of the ABS/Brake warning light.
🚨 Repair Difficulty Tier
- Difficulty Rating: Professional Only
This repair involves working directly with the electric brake booster assembly, which is a critical safety system requiring specialized bleeding procedures and precise electrical diagnostics. A technician will need a professional-grade scan tool capable of bi-directional controls and a digital multimeter to safely isolate the short circuit without damaging the EBCM. Due to the safety-critical nature of brake assist systems, DIY repair is strongly discouraged.
🛠️ Resolution Steps
- Step 1: Preliminary Inspection
Begin by visually inspecting the wiring harness and connector leading to the Brake Booster Motor Position Sensor. Look for signs of chafing, pinched wires, or corrosion where the 5V reference wire might be shorting against a power supply wire (such as a 12V ignition or battery source wire) within the harness loom near the booster assembly. - Step 2: Diagnostic Verification
Using a scan tool, access the EBCM live data stream and monitor the voltage reported on the Position Sensor Supply Circuit to confirm the high voltage condition is active. Next, disconnect the sensor connector and use a digital multimeter to check for voltage on the reference wire pin. If voltage remains high even when disconnected from the sensor (with the ignition on and the connector unplugged), this confirms a wiring short to power upstream between the EBCM and the connector, rather than an internal sensor failure. - Step 3: Resolution & Reset Process
If the wiring is confirmed to be shorted, repair or replace the damaged harness section, ensuring sufficient wire loom protection is reinstalled to prevent recurrence. If the wiring tests normal but the high voltage persists only when the sensor is connected, the booster motor/position sensor assembly itself will require replacement. After the repair, use the scan tool to clear the EBCM fault codes and perform any required brake system bleeding and calibration (zero-point reset) procedures specific to the electric booster unit to ensure proper pedal feel and assist function are restored.
📦 Parts, Labor, and Budget Estimates
- Required Components/Software: Brake Booster Wiring Harness Repair Kit OR Electric Brake Booster/Motor Assembly, Professional Bi-Directional Scan Tool
- Average Component Price: $150 – $450 USD (highly dependent on whether a simple wire repair or full booster assembly replacement is needed)
- Estimated Labor Hours: 1.5 – 3.0 hours
- Total Estimated Budget: $300 – $750 USD