C05BA

Code

Generic C — Chassis

Brake Booster Motor A Position Sensor Supply Circuit High

Brand: Generic

Type: C — Chassis

Views: UK: 23 EN: 44 RU: 32

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short in sensor supply wire to battery or ignition voltage
Faulty brake booster motor position sensor (internal short/failed regulator)
Poor or corroded connector or pin damage at sensor or module
Control module (brake/ABS module) internal fault driving the supply high
Aftermarket wiring or incorrect replacement parts
Water intrusion or chafing causing intermittent shorts

Symptoms

Brake booster motor fault lamp or ABS/traction warning lamp illuminated (if applicable)
Diagnostic trouble code stored for sensor supply high
Reduced or degraded brake assist or related fault messages (depends on system)
Possible inability to perform certain brake system self-tests

What to check

Retrieve freeze frame and live data with a scan tool; confirm code and any related codes
Visually inspect sensor connector, wiring harness, and brake booster motor for damage, corrosion, or water intrusion
Check for aftermarket devices or recent repairs near the harness that could have altered wiring
With ignition ON (engine OFF), measure the sensor supply/reference voltage at the sensor connector with a quality digital multimeter
Back-probe the module harness connector to see if the supply voltage is present at the module side with the sensor disconnected
Check wiring continuity and short-to-voltage between the supply wire and battery positive

Signal parameters

Normal sensor reference/supply voltage: approximately 5.0 V (typical systems 4.5–5.5 V)
Fault condition: supply >5.5 V or supply at or near battery voltage (~9–16 V on running vehicle)
Sensor output (position) expected within 0.5–4.5 V range depending on position; supply high will likely push readings out of expected range

Diagnostic algorithm

Record freeze frame and live data, then clear the code and attempt to reproduce the fault
Perform a visual inspection of sensor, harness, and connectors for damage, corrosion, pins pushed out, or signs of water intrusion
With ignition ON (engine OFF), back-probe the sensor connector supply pin and measure voltage relative to chassis ground. Compare to expected ~5 V. If high, proceed.
Disconnect the sensor connector and measure supply voltage at the harness side (module side). If the supply is still high with the sensor disconnected, suspect wiring short to battery or module fault.
If supply is normal with sensor disconnected, test or replace the sensor (bench test if possible). Reconnect and re-check.
If supply remains high at module side with sensor disconnected, perform continuity tests: check for short-to-voltage between supply wire and battery positive, and for short-to-ground faults. Repair wiring as needed.
If wiring checks out (no short to battery) and supply at the module connector is high, suspect internal module fault. Verify with wiring diagrams and, where possible, swap module with known-good unit or consult manufacturer service info/TSBs before replacement.
After repairs, clear codes and road-test or cycle system to confirm the fault does not return. Re-scan for stored codes and verify proper supply and sensor outputs.

Likely causes

Shorted supply wire to battery/ignition circuit
Failed position sensor with internal short to Vbatt or internal regulator failure
Corroded/contaminated connector causing abnormal voltage reading

Fault status

⚠️ Status

Brake Booster Motor A position sensor supply (reference) voltage is higher than expected. Investigate for short to battery, sensor failure, wiring/connector problems, or control module fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours