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Home / DTC / C101A — Pressure sensor of vacuum Brake vacuum pump left

C101A — Pressure sensor of vacuum Brake vacuum pump left

Detailed page for trouble code C101A.

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Code

C101A

LAND ROVER C — Chassis

Pressure sensor of vacuum Brake vacuum pump left

Brand: LAND ROVER
Type: C — Chassis
Views: UK: 14 EN: 29 RU: 11
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Page language: EN

Causes

  • Failed/failed‑to‑calibrate left brake vacuum pump pressure sensor
  • Open, shorted or corroded wiring or connector at the sensor
  • Poor ground or lost reference supply to the sensor
  • Vacuum leak in supply hose, check valve or connections to the pump
  • Mechanical fault or electrical failure of the vacuum pump itself
  • Obstruction or blockage in vacuum lines or filter

Symptoms

  • Brake assist/ABS/warning indicator lamp illuminated
  • Increased brake pedal travel or hard pedal feel (reduced boost)
  • Reduced brake assistance at idle or low engine speed
  • Possible engine idle or load changes if pump is engine‑driven
  • Stored diagnostic trouble code(s) and related fault data in vehicle controller

What to check

  • Scan for stored codes and freeze‑frame/fault data with an OEM or qualified scan tool
  • Perform a thorough visual inspection of the left pump sensor, connector and wiring for damage, corrosion, or loose pins
  • Backprobe sensor connector and check for proper reference (usually 5V) and ground at key ON/engine running states
  • Monitor live sensor voltage/pressure values with scan tool or multimeter while exercising brake pump and during engine idle/load
  • Inspect vacuum hoses, check valve and fittings for leaks, cracks or blockages
  • Use a vacuum gauge at the pump/sensor port to verify actual vacuum level under various conditions

Signal parameters

  • Typical sensor reference: +5 V supply (verify with vehicle data)
  • Typical signal output: approximately 0.5–4.5 V (sensor mid‑range ≈2.5 V at nominal vacuum) — confirm exact values with OEM data
  • Ground continuity between sensor ground and chassis/ECU ground should be near 0 Ω
  • Expected vacuum at pump/sensor (nominal): verify with OEM spec; typical brake vacuum systems produce significant vacuum at idle — confirm with a vacuum gauge

Diagnostic algorithm

  1. Read and record all DTCs, freeze frame and live data with an OEM scan tool; note time‑stamped events. 2) Visually inspect sensor, connector and harness for obvious damage or corrosion; repair as needed. 3) With ignition ON, backprobe the sensor connector: verify reference voltage (≈5 V), sensor ground, and measure signal voltage. Compare to OEM expected values. 4) Monitor live sensor signal while operating the brake vacuum pump (or cycling ignition if applicable). Look for slow response, stuck high/low, or intermittent signal. 5) Perform a wiggle test of wiring/connectors while watching live data to find intermittent opens/shorts. 6) Fit a vacuum gauge to the pump/sensor port and measure vacuum under idle and during pump operation. Inspect hoses and check valve for leaks or restrictions. 7) If wiring/supply/ground are correct and vacuum is present but signal is incorrect, replace the left pressure/vacuum sensor and retest. 8) If sensor replacement does not clear the issue and vacuum is low, diagnose the vacuum pump (mechanical/electrical) and related control components; repair/replace as required. 9) After repairs, clear codes, perform functional tests and road test while monitoring live data to confirm the fault is resolved.

Likely causes

  • Faulty pressure/vacuum sensor (most common)
  • Damaged connector or pin corrosion at sensor
  • Broken or shorted harness between sensor and ABS/PCM module
  • Vacuum leak or failed check valve reducing vacuum at the sensor
  • Vacuum pump not producing expected vacuum due to mechanical/electrical failure

Fault status

⚠️ Status
Left brake vacuum pump pressure sensor circuit fault — signal out of range or missing (C101A).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

C101B C1220 C1234 C1500 C1A00
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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