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DTC codes / C00xx · Brakes, steering and suspension / C0047

C0047Brake Booster Pressure Sensor

C0047 means the anti-lock brake system (ABS) module has detected a fault in the brake booster pressure sensor circuit, which monitors the vacuum or hydraulic pressure assisting your brake pedal. The computer compares the sensor signal against expected values and flags the code when the reading is out of range, erratic, or missing entirely.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • Illumination of the ABS warning light, and often the traction control and stability control lights as well
  • A brake pedal that feels unusually hard or requires more effort to push
  • Reduced or inconsistent power brake assist, especially during the first few presses after startup
  • A soft or spongy pedal if the sensor fault is accompanied by a pressure leak
  • Often no symptoms besides the warning light, with normal brake feel in many cases

Common causes, most likely first

  1. Failed brake booster pressure sensor sending an incorrect or no signal
  2. Damaged, corroded, or disconnected wiring and connector pins at the sensor or ABS module
  3. Vacuum leak in the brake booster hose, check valve, or booster diaphragm affecting the pressure reading
  4. Faulty ABS control module unable to process the sensor input correctly
  5. Contaminated or restricted vacuum supply line causing the sensor to read outside normal parameters
  6. Low brake fluid or air in the hydraulic system altering pressure readings at the sensor

How to diagnose and fix it

  1. Connect a scan tool and read all ABS and powertrain codes to confirm C0047 is current and not a stored history code from a past event
  2. Inspect the brake booster pressure sensor connector and wiring for corrosion, chafing, or loose pins, and repair as needed
  3. Check the vacuum hose and check valve between the booster and intake manifold for cracks, collapse, or leakage using a vacuum gauge
  4. Test the brake booster pressure sensor signal with a multimeter or scan tool live data, comparing voltage or pressure readings against the manufacturer's specification
  5. Verify brake fluid level and condition, and bleed the system if air or contamination is suspected
  6. Replace the brake booster pressure sensor if testing confirms it is out of specification, then clear codes and verify the repair with a road test
  7. If the sensor and wiring test good, diagnose the ABS module for internal faults or software issues before replacement

What the pressure sensor code really tells you

  • A vacuum leak at the booster check valve or hose often sets C0047 because the sensor reads low pressure even though the sensor itself is healthy, so always smoke-test or vacuum-test the supply line first.
  • The brake booster pressure sensor is sometimes integrated into the ABS module or the booster assembly on certain vehicles, meaning a sensor fault may require replacing a larger and more expensive component.
  • C0047 can be set by a momentary voltage drop or low battery during cranking, so check battery health and charging system output before condemning the sensor.
  • A misadjusted or sticking brake pedal position switch can cause the ABS module to see implausible pressure sensor values and set this code, so inspect pedal free play and switch operation.
  • After replacing the sensor, some vehicles require a relearn or calibration procedure with a scan tool to clear the code permanently, so do not assume a new part alone fixes it.

Can I keep driving with C0047?

You can usually drive the vehicle with C0047, but be aware that power brake assist may be reduced or inconsistent, so increase following distance and avoid heavy braking until the fault is repaired. If the pedal becomes very hard or braking performance drops noticeably, stop driving and have the system inspected immediately.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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