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Home / DTC / C05C9 — Brake Pressure Sensor Supply Circuit

C05C9 — Brake Pressure Sensor Supply Circuit

Detailed page for trouble code C05C9.

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C05C9

Generic C — Chassis

Brake Pressure Sensor Supply Circuit

Brand: Generic
Type: C — Chassis
Views: UK: 20 EN: 24 RU: 18
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Page language: EN

Causes

  • Blown fuse or tripped circuit protecting sensor supply
  • Open or high-resistance wiring between ECU and sensor (broken wire, damaged insulation)
  • Short to battery voltage or short to ground on the sensor supply wire
  • Corroded, loose, or damaged sensor connector pins
  • Faulty brake pressure sensor
  • Faulty ECU/ABS module internal supply or connector

Symptoms

  • ABS, ESC or brake warning lamp on the dash
  • Stored C05C9 and possibly related chassis/ABS codes
  • Loss of ABS or ESC function; backup/brake assist may be limited
  • Erroneous brake pressure readings or implausible values in live data
  • Intermittent or permanent limp mode of stability control systems

What to check

  • Retrieve all related codes and freeze frame data with a scan tool
  • Visually inspect harness and connectors at brake pressure sensor and ABS module for corrosion, damage, pin push-out, water
  • Verify battery voltage and main power fuses (key ON, engine OFF)
  • Check fuse or fusible link that supplies the ABS/sensor circuits
  • Backprobe sensor connector with key ON to measure supply/reference voltage and ground
  • Measure signal voltage from sensor at rest and while applying pressure (or actuating brake system)

Signal parameters

  • Typical reference/supply: 5 V (many systems) — acceptable approx. 4.75–5.25 V (verify vehicle-specific service data)
  • Signal output range: about 0.5–4.5 V depending on pressure (varies by sensor type)
  • Short to battery would show ~12 V on supply; short to ground shows ~0 V
  • Expected supply current: low (tens of milliamps); high current may indicate short
  • Resistance of supply circuit should be low (< a few ohms for short segments); open circuit shows very high/OL

Diagnostic algorithm

  1. Read and record all stored and pending codes and freeze frame data with a scan tool. Note related ABS/brake codes.
  2. Perform a visual inspection of the brake pressure sensor connector, wiring harness routing, and ABS module connector for damage, corrosion, or water ingress.
  3. Check relevant fuses and relays for the ABS/sensor power supply; replace if blown and re-test.
  4. With key ON (engine OFF), backprobe the sensor supply terminal. Compare to expected reference voltage from service data (commonly ~5 V). Record value.
  5. Check sensor ground by measuring voltage drop between sensor ground and chassis with key ON. Should be near 0 V.
  6. Measure sensor signal voltage at rest and while applying brake pressure (or using a pressure pump) and confirm values change plausibly and remain within expected range.
  7. If supply voltage is missing or out of range, isolate harness: disconnect sensor and measure supply at harness side and at ABS/ECU connector. Perform continuity and short-to-ground/battery tests.
  8. Wiggle wiring harness and connectors while monitoring live data and DTCs to find intermittent faults.
  9. If wiring and supply check good, swap in a known-good brake pressure sensor or bench-test the sensor. Replace sensor if faulty.
  10. If wiring and sensor are good, inspect/replace ABS/ECU connector or evaluate the module’s internal power regulator; consult manufacturer service data for module replacement/testing.
  11. Clear codes and perform a road test/functional test to verify the repair. Re-scan for reappearance.

Likely causes

  • Corroded/loose connector at the brake pressure sensor
  • Open or shorted supply wire in the harness (common at harness flex points)
  • Blown fuse or fusible link supplying sensor reference
  • Failed brake pressure sensor
  • Internal ABS/ECU supply regulator fault

Fault status

⚠️ Status
Brake pressure sensor supply circuit fault — reference/supply voltage open, shorted, or out of range. May disable ABS/ESC functions.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

C05C8 C05CA C05CB C1234 C1210
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