C1934

Code

Other C — Chassis

HPU (Hydraulic Pump Unit) Pressurisation Failure

Brand: Other

Type: C — Chassis

Views: UK: 26 EN: 44 RU: 32

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Causes

Low or contaminated hydraulic fluid in reservoir
Hydraulic pump/motor failure (mechanical wear or seized)
Electrical supply fault: blown fuse, faulty relay, poor battery/ground
Open or short in pump motor wiring or connector corrosion
Pressure sensor (transducer) failure or bad signal
Internal or external hydraulic leak (hoses, fittings, valves)

Symptoms

Warning light or message for hydraulic/HPU fault
Loss or reduction of hydraulic-assisted systems (e.g., suspension, steering assist, braking assist depending on system)
HPU runs continuously or fails to run
Pump noise is abnormal (grinding, whining) or is silent when commanded
Slow or no response of hydraulic actuators
Intermittent operation or fault clears/reappears

What to check

Read manufacturer codes and live data with a capable scan tool; record freeze/frame data
Visual inspection for fluid leaks, damaged hoses, and disconnected/corroded connectors at HPU
Check hydraulic fluid level and condition in the reservoir
Verify fuses and relays for HPU power circuit and test relay operation
Measure battery voltage at key on and during pump command; check for voltage drop
Inspect ground connections and wiring harness for chafing or opens/shorts

Signal parameters

HPU supply voltage: nominal battery voltage (~12 V) when commanded (allow for drop under load)
Pump motor current draw: should be within manufacturer specified range (typically tens of amps under load) — abnormally high or open indicates fault
Pressure sensor output: typical transducer range 0.5–4.5 V or 0–5 V depending on sensor; should change as pressure changes
Pressure build time: HPU should reach commanded pressure within specified time (manufacturer data) — prolonged/no build indicates fault
Control/comm signals: CAN/serial messages to/from HPU controller should be present and valid

Diagnostic algorithm

Connect a factory-level scan tool and read all stored and pending codes. Note freeze data and live pressure/PIDs related to HPU.
Attempt to command HPU ON via the scan tool while monitoring supply voltage, pump current (if available), and pressure PID. Observe whether the pump runs and whether pressure rises.
Check power and ground at the HPU connector with the pump commanded ON. Verify fuses and relays in the supply circuit and inspect wiring for corrosion or damage.
Inspect reservoir fluid level and condition. Top up with correct fluid only if contaminated check is not suspected; if contamination suspected, plan fluid change and system flush per manufacturer procedures.
Visually inspect hydraulic lines, fittings, and valves for leaks. Pressure-test the hydraulic circuit if safe and possible to locate leaks.
If pump does not run electrically, measure motor winding resistance and current draw during attempted operation. Replace pump if motor shows open/short or excessive current.
If pump runs but pressure does not build, isolate and test pressure sensor: compare sensor output to an independent mechanical pressure gauge. Replace sensor if readings do not match.
Check HPU control valves/solenoids for sticking or internal leakage. Perform manufacturer-recommended bench or functional tests.
If electrical and hydraulic components check good but fault persists, examine module communications and software — reprogram or replace control module only after confirming sensors, wiring, and HPU integrity.
After repairs, clear codes, re-test system through several pressure cycles, and road-test to confirm proper operation. Ensure no leaks and that pressures meet specification.