C1777

Code

LAND ROVER C — Chassis

Vacuum pressure - circuit failure

Brand: LAND ROVER

Type: C — Chassis

Views: UK: 12 EN: 22 RU: 17

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Page language: EN

Causes

Open or shorted wiring between vacuum pressure sensor and control module
Corroded or loose connector at the sensor or module
Faulty vacuum pressure sensor (internal failure)
Failed or weak vacuum pump or reservoir
Blocked, collapsed or disconnected vacuum hose or line
Blown fuse or failed relay supplying sensor/pump power

Symptoms

ABS/Brake warning lamp or other related dash warning lamps
Harder than normal brake pedal (reduced vacuum assist) or inconsistent brake feel
Related system faults depending on application (suspension leveling, HVAC actuator faults)
Stored DTC C1777 (may be accompanied by other codes)
Possible engine running irregularities if vacuum supply to engine systems affected

What to check

Read and record all stored DTCs and freeze frame data with a capable scan tool
Check live vacuum pressure sensor value and compare to expected values
Visual inspection of vacuum hoses, reservoir and pump for damage or disconnection
Inspect sensor and module connectors for corrosion, bent pins or water ingress
Check fuses and relays related to vacuum pump and sensor power
Backprobe sensor connector and verify reference voltage, signal voltage and ground

Signal parameters

Reference supply (typical): ~5.0 V reference from control module (verify with OEM spec)
Signal output: ~0.5–4.5 V proportional to vacuum (exact scale is manufacturer-specific — consult service data)
Ground:
Typical vacuum levels (engine idling/charging vacuum): roughly 18–22 inHg (≈60–75 kPa) depending on engine and conditions — check OEM values
Pump supply (if electrically driven): switched battery voltage (approx. 12 V) when commanded

Diagnostic algorithm

Connect a diagnostic scanner, record C1777 and any related codes, and note freeze-frame/live data.
Inspect vacuum hoses, reservoir, check valve and pump for obvious damage or disconnection; repair as required.
Visually inspect sensor and module connectors; disconnect, clean contacts and reseat; check for corrosion or water entry.
With ignition ON (engine OFF), backprobe the sensor connector: confirm reference voltage (~5V), good ground and measure signal voltage. Compare to expected idle/engine-run values in OEM data.
Start engine and monitor live vacuum pressure readings. If the signal is absent or erratic, perform wiggle tests on harness while observing signal.
If signal wiring shows open/short, trace and repair wiring using wiring diagrams; repair connector pins or replace harness section as needed.
If wiring and connectors are good but readings are incorrect, test or replace the vacuum pressure sensor with a known-good unit and re-check.
Test vacuum pump operation: verify pump receives power when commanded and produces expected vacuum to the reservoir; repair/replace pump or check valves if weak.
After repairs, clear codes, perform a relearn (if required by OEM), and road test to confirm the fault does not return.
If fault persists after sensor, wiring and pump verified, consider module/software diagnosis or dealer-level diagnostic procedures.

Likely causes

Damaged harness or pin pushed out at sensor connector
Sensor internal failure (common if wiring checks good)
Vacuum pump or reservoir not generating expected vacuum (mechanical failure)
Vacuum hose split/collapsed or one-way check valve failed
Intermittent connector corrosion causing open/short under load

Fault status

⚠️ Status

Vacuum pressure circuit fault detected — sensor circuit open/short/invalid signal or loss of expected vacuum input.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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