3 hours ago
The Bobcat 753 skid steer is one of the most widely used compact loaders in North America, known for its simplicity, reliability, and compatibility with a wide range of hydraulic attachments. Many units have accumulated thousands of hours in landscaping, agriculture, and construction work. As these machines age, electrical and hydraulic monitoring systems—especially the early BOSS control system—can trigger error codes such as HP‑1 and HP‑3. These warnings often confuse new owners because they may appear intermittently or only when certain sensors are connected.
Understanding the meaning of these codes, the role of the hydraulic charge pressure switch, and the interaction between the ignition circuit and auxiliary hydraulics is essential for diagnosing the issue.
Background of the Bobcat 753 and the BOSS System
The Bobcat 753 was introduced during a period when manufacturers were transitioning from purely mechanical controls to early electronic monitoring systems. Bobcat’s BOSS (Bobcat Operation Sensing System) was designed to protect the machine by monitoring hydraulic pressure, engine conditions, and operator inputs.
Key characteristics of the 753 include:
Understanding HP‑1 and HP‑3 Warnings
HP‑1 and HP‑3 codes generally relate to hydraulic pressure monitoring. When the charge pressure switch detects a condition outside its expected range, the BOSS system triggers an alarm and may shut the machine down to prevent damage.
In the case described in the retrieved content, the machine runs normally when the charge pressure switch is unplugged but triggers HP‑1/HP‑3 warnings and eventually shuts down when the switch is connected. This behavior strongly suggests:
Ignition Switch Influence on Auxiliary Hydraulics
Another symptom described is the machine starting and immediately dying unless the operator presses the auxiliary hydraulic buttons before cranking. This is not normal behavior and suggests an electrical interaction between the ignition switch and the BOSS system.
Experienced technicians note that:
Why the Charge Pressure Switch Causes Shutdown
The charge pressure switch is designed to protect the hydrostatic pumps. If the BOSS system believes charge pressure is too low, it assumes the pumps may be starved of oil and shuts the machine down.
Possible causes include:
Anecdotes from the Field
Many operators who grew up using older Bobcat machines recall that the BOSS system was both a blessing and a curse. One contractor shared that his 753 would occasionally shut down in the middle of auger work, only to restart normally after unplugging the charge pressure switch. Another mechanic remembered replacing multiple sensors before discovering that the real culprit was a corroded ground wire hidden behind the engine.
These stories highlight the importance of checking simple electrical issues before replacing expensive components.
Bobcat Company Background
Bobcat, founded in the 1950s, became the pioneer of the modern skid steer loader. The 700‑series machines, including the 753, were among the company’s best‑selling models, with tens of thousands produced. Their popularity stemmed from:
Practical Recommendations
HP‑1 and HP‑3 warnings on a Bobcat 753 typically point to issues with the charge pressure switch or the BOSS monitoring system. While the machine may run normally with the switch unplugged, the underlying electrical or sensor fault should be addressed to ensure long‑term reliability. With proper troubleshooting—starting with the ignition switch, wiring, and charge pressure sensor—most of these issues can be resolved without major repairs.
Understanding the meaning of these codes, the role of the hydraulic charge pressure switch, and the interaction between the ignition circuit and auxiliary hydraulics is essential for diagnosing the issue.
Background of the Bobcat 753 and the BOSS System
The Bobcat 753 was introduced during a period when manufacturers were transitioning from purely mechanical controls to early electronic monitoring systems. Bobcat’s BOSS (Bobcat Operation Sensing System) was designed to protect the machine by monitoring hydraulic pressure, engine conditions, and operator inputs.
Key characteristics of the 753 include:
- A 1,300–1,400 lb rated operating capacity
- A simple mechanical drive system
- A hydraulic system designed for auxiliary attachments
- Early electronic monitoring through the BOSS module
- Charge pressure switch: A sensor that monitors hydraulic charge pressure feeding the hydrostatic pumps.
- Auxiliary hydraulics: Additional hydraulic circuits used to power attachments such as augers or trenchers.
- BOSS system: Bobcat’s early electronic safety and monitoring system.
- Micron filter: A fine filter element used to protect sensitive hydraulic components.
Understanding HP‑1 and HP‑3 Warnings
HP‑1 and HP‑3 codes generally relate to hydraulic pressure monitoring. When the charge pressure switch detects a condition outside its expected range, the BOSS system triggers an alarm and may shut the machine down to prevent damage.
In the case described in the retrieved content, the machine runs normally when the charge pressure switch is unplugged but triggers HP‑1/HP‑3 warnings and eventually shuts down when the switch is connected. This behavior strongly suggests:
- A faulty charge pressure switch
- A clogged or partially restricted micro‑filter
- Internal leakage causing incorrect pressure readings
- A wiring or grounding issue
- A BOSS module fault
Ignition Switch Influence on Auxiliary Hydraulics
Another symptom described is the machine starting and immediately dying unless the operator presses the auxiliary hydraulic buttons before cranking. This is not normal behavior and suggests an electrical interaction between the ignition switch and the BOSS system.
Experienced technicians note that:
- Aftermarket ignition switches often cause erratic auxiliary hydraulic behavior
- Incorrect voltage supply to the BOSS module can prevent proper startup
- The auxiliary buttons may be back‑feeding power into the system, temporarily stabilizing it
Why the Charge Pressure Switch Causes Shutdown
The charge pressure switch is designed to protect the hydrostatic pumps. If the BOSS system believes charge pressure is too low, it assumes the pumps may be starved of oil and shuts the machine down.
Possible causes include:
- A failing switch sending incorrect signals
- Internal leakage in the switch allowing hydraulic oil into the electrical cavity
- A damaged wiring harness
- A BOSS module that is misinterpreting the signal
Anecdotes from the Field
Many operators who grew up using older Bobcat machines recall that the BOSS system was both a blessing and a curse. One contractor shared that his 753 would occasionally shut down in the middle of auger work, only to restart normally after unplugging the charge pressure switch. Another mechanic remembered replacing multiple sensors before discovering that the real culprit was a corroded ground wire hidden behind the engine.
These stories highlight the importance of checking simple electrical issues before replacing expensive components.
Bobcat Company Background
Bobcat, founded in the 1950s, became the pioneer of the modern skid steer loader. The 700‑series machines, including the 753, were among the company’s best‑selling models, with tens of thousands produced. Their popularity stemmed from:
- Simple mechanical drivetrains
- Strong dealer support
- Compatibility with a wide range of attachments
- Ease of maintenance
Practical Recommendations
- Inspect the charge pressure switch for internal hydraulic leakage.
- Replace the switch if unplugging it eliminates the warning.
- Check wiring harnesses for corrosion or loose connections.
- Verify that the ignition switch is OEM, not aftermarket.
- Clean or replace the 10‑micron filter behind the switch.
- Inspect grounds and battery connections for voltage drops.
- If warnings persist, consider bypassing the BOSS system with a mechanical workaround—common on older machines.
HP‑1 and HP‑3 warnings on a Bobcat 753 typically point to issues with the charge pressure switch or the BOSS monitoring system. While the machine may run normally with the switch unplugged, the underlying electrical or sensor fault should be addressed to ensure long‑term reliability. With proper troubleshooting—starting with the ignition switch, wiring, and charge pressure sensor—most of these issues can be resolved without major repairs.
