Code
C0587
Generic
C — Chassis
Brake Booster Motor A Position Sensor Circuit/Open
Views:
UK: 22
EN: 29
RU: 18
AI status
Completed
Completed
100%
Causes
- Open or broken signal wire between sensor and control module
- Corroded, loose or damaged connector/pins at the sensor or module
- Blown fuse or failed relay supplying the brake booster module
- Faulty brake booster motor position sensor
- Internal failure of the brake booster/actuator assembly or its control module
- Poor or missing ground at sensor or control module
Symptoms
- Brake system warning light or ABS/ESC lamp illuminated
- Reduced or no power brake assist — hard or heavier brake pedal
- Longer pedal travel or delayed brake response
- Stored or active DTCs related to brake booster/position sensor
- Possible limp-in/limited braking/traction control intervention depending on vehicle
What to check
- Retrieve all related DTCs and freeze frame/live data with a scan tool
- Visually inspect brake booster and harness for damage, corrosion, pinched wires, and crushed connectors
- Check for blown fuses and faulty relays that supply the booster/control module
- Wiggle harness and operate the pedal/booster while watching live data for intermittent changes
- Backprobe connector and check for proper reference voltage, ground continuity and signal voltage while operating
- Measure continuity and resistance between sensor connector and control module pin to identify open circuits
Signal parameters
- Typical reference voltage: ~5 V (varies by manufacturer)
- Sensor signal: variable voltage proportional to position — commonly ~0.5–4.5 V or 0–5 V depending on design (manufacturer-specific)
- Supply voltage for motor/actuator: switched 12 V (verify per vehicle)
- Open-circuit condition: no signal or infinite resistance reported by continuity check (OL)
- Ground: near 0 Ω to chassis ground (verify continuity)
Diagnostic algorithm
- Read and record fault code(s), freeze-frame data and live sensor values with a scan tool. Note if code is current or historic.
- Visually inspect booster's connector, wiring harness and module for damage, corrosion or loose pins. Repair any obvious damage.
- Check related fuses and relays for the brake booster/control module circuit; replace if blown and retest.
- With ignition ON, backprobe connector: verify reference (5 V typical), sensor signal and ground presence. If reference or ground missing, trace to power/ground source.
- If voltages present, actuate brake booster (or have assistant press pedal, or use diagnostic actuator) while monitoring signal. If signal does not change, suspect sensor or internal booster fault.
- Perform continuity/ohm test from sensor pins to the control module pins to find opens or high resistance. Repair/replace wiring as required.
- If wiring and supplies are good but signal absent or out of range, replace the brake booster position sensor or the booster/actuator assembly per service manual.
- After repair, clear codes, perform functional tests and a road test to confirm proper brake assist and that the code does not return.
Likely causes
- Open or damaged signal/return wiring
- Corroded or poorly seated connector at the sensor
- Failed position sensor inside the brake booster/actuator
- Blown/loose supply or ground to the booster control module
Fault status
Status
Brake Booster Motor A Position Sensor Circuit/Open — the control module detects an open or interrupted signal from the brake booster motor/position sensor; brake assist may be reduced or disabled until the circuit is repaired.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Code
C0587
HUMMER
C — Chassis
Left Rear Solenoid Circuit Low
Views:
UK: 10
EN: 14
RU: 9
AI status
Completed
Completed
100%
Causes
- Open or broken signal wire between sensor and control module
- Corroded, loose or damaged connector/pins at the sensor or module
- Blown fuse or failed relay supplying the brake booster module
- Faulty brake booster motor position sensor
- Internal failure of the brake booster/actuator assembly or its control module
- Poor or missing ground at sensor or control module
Symptoms
- Brake system warning light or ABS/ESC lamp illuminated
- Reduced or no power brake assist — hard or heavier brake pedal
- Longer pedal travel or delayed brake response
- Stored or active DTCs related to brake booster/position sensor
- Possible limp-in/limited braking/traction control intervention depending on vehicle
What to check
- Retrieve all related DTCs and freeze frame/live data with a scan tool
- Visually inspect brake booster and harness for damage, corrosion, pinched wires, and crushed connectors
- Check for blown fuses and faulty relays that supply the booster/control module
- Wiggle harness and operate the pedal/booster while watching live data for intermittent changes
- Backprobe connector and check for proper reference voltage, ground continuity and signal voltage while operating
- Measure continuity and resistance between sensor connector and control module pin to identify open circuits
Signal parameters
- Typical reference voltage: ~5 V (varies by manufacturer)
- Sensor signal: variable voltage proportional to position — commonly ~0.5–4.5 V or 0–5 V depending on design (manufacturer-specific)
- Supply voltage for motor/actuator: switched 12 V (verify per vehicle)
- Open-circuit condition: no signal or infinite resistance reported by continuity check (OL)
- Ground: near 0 Ω to chassis ground (verify continuity)
Diagnostic algorithm
- Read and record fault code(s), freeze-frame data and live sensor values with a scan tool. Note if code is current or historic.
- Visually inspect booster's connector, wiring harness and module for damage, corrosion or loose pins. Repair any obvious damage.
- Check related fuses and relays for the brake booster/control module circuit; replace if blown and retest.
- With ignition ON, backprobe connector: verify reference (5 V typical), sensor signal and ground presence. If reference or ground missing, trace to power/ground source.
- If voltages present, actuate brake booster (or have assistant press pedal, or use diagnostic actuator) while monitoring signal. If signal does not change, suspect sensor or internal booster fault.
- Perform continuity/ohm test from sensor pins to the control module pins to find opens or high resistance. Repair/replace wiring as required.
- If wiring and supplies are good but signal absent or out of range, replace the brake booster position sensor or the booster/actuator assembly per service manual.
- After repair, clear codes, perform functional tests and a road test to confirm proper brake assist and that the code does not return.
Likely causes
- Open or damaged signal/return wiring
- Corroded or poorly seated connector at the sensor
- Failed position sensor inside the brake booster/actuator
- Blown/loose supply or ground to the booster control module
Fault status
Status
Brake Booster Motor A Position Sensor Circuit/Open — the control module detects an open or interrupted signal from the brake booster motor/position sensor; brake assist may be reduced or disabled until the circuit is repaired.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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