Fault Phenomenon: Hongda HBT80 pumps normally when cold. After reaching operating temperature (high system pressure), the S-pipe fails to reverse, system pressure spikes instantly, with no alarm on the dashboard.

Troubleshooting Process:
– Checked S-pipe swing cylinder: piston rod not bent, seals intact.
– Checked reversing solenoid valve: coil energized and pulls normally, spool not stuck.
– Checked pressure sensor wiring: connections secure, no short circuit.
– Measured pressure sensor feedback at operating temperature: found voltage drift exceeds allowable range.

Root Cause: Zero-point drift of the main system pressure sensor misleads the control system.

Required Parts: Main system pressure sensor.