C058C

Code

Generic C — Chassis

Brake Booster Motor B Position Sensor Circuit Low

Brand: Generic

Type: C — Chassis

Views: UK: 22 EN: 22 RU: 23

AI status

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Page language: EN

Causes

Open or shorted wiring in the brake booster motor B position sensor circuit
Corroded, loose, or damaged connector at the booster motor/sensor
Failed brake booster motor position sensor (potentiometer/Hall sensor)
Insufficient reference voltage or poor ground at sensor
Blown fuse or relay feeding the booster motor/sensor circuit
Internal failure in the brake booster motor/actuator assembly

Symptoms

Brake warning lamp, ABS or traction control lamp illuminated
Reduced or no power brake assist — hard brake pedal
Increased pedal travel and longer stopping distances
Stored DTC and inability to enable normal brake assist
Possible limp or reduced braking mode indicated by instrument cluster

What to check

Read and record DTCs and freeze-frame data with a scan tool; view live data for brake booster motor position
Verify battery voltage is within spec (12.4–14.5 V) before testing
Visually inspect connector at brake booster motor for corrosion, bent pins, water intrusion, or damage
Check related fuses and relays for continuity and proper operation
Backprobe the sensor connector to verify reference voltage and ground
Wiggle wiring harness while monitoring live data to detect intermittent faults

Signal parameters

Reference supply: typically 5 V (verify with manufacturer data)
Sensor output expected: approx. 0.5–4.5 V (depending on position) — low-level fault when below expected lower threshold (manufacturer-specific)
Ground: near 0.0–0.2 V reference at sensor ground pin
Resistance: position potentiometer style sensors commonly 1 kΩ–20 kΩ (check OEM spec)
Signal behavior: smooth, continuous change with actuator movement; no open circuit or stuck low

Diagnostic algorithm

Connect scan tool, record DTCs and live data for brake booster motor position. Note stored freeze-frame conditions.
Verify battery voltage and charge if low. Low system voltage can cause false low-signal DTCs.
Inspect all connectors, harness sections, and mounting of the brake booster motor assembly for damage or corrosion. Repair as needed.
Check related fuses and relays. Replace any blown fuses and retest.
Backprobe the sensor connector with ignition ON (engine off). Measure reference voltage, sensor output, and ground using a multimeter. Compare to expected signal parameters.
Operate booster motor (with scan tool command or by cycling brake system where applicable) and observe sensor output for smooth change. A stuck or constant low reading indicates sensor or internal fault.
Perform continuity and resistance checks on wiring between the sensor connector and ABS/ECM connector. Repair open/shorts.
If wiring and power/ground are good but signal remains low, remove and bench-test or replace the brake booster motor/position sensor assembly per manufacturer procedure.
After repair, clear codes and perform road test or commanded tests to confirm correct operation and absence of DTC.

Likely causes

Damaged connector or corroded pins at the brake booster motor
Broken or shorted wiring between booster motor sensor and control module
Failed position sensor inside the electric booster motor assembly
Blown fuse or missing reference voltage to the sensor
Poor sensor ground connection

Fault status

⚠️ Status

Brake Booster Motor B Position Sensor Circuit Low — sensor output below acceptable range or missing signal; control module has limited or no position feedback.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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