Bobcat M0521 (05-21) Fault Code: Hydraulic Charge Pressure Out of Range High
Also shown on the panel as 05-21
Hydraulic Charge Pressure Out of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
M0521 (panel code 05-21) sets when the gateway controller sees a short to supply voltage for 30 seconds on the hydraulic charge pressure sensor signal wire. It runs with the key switch in run/enter and is self resetting once the fault clears.
Medium severity. The hydraulic charge circuit is being monitored electrically, not mechanically overloaded, so the machine is not in immediate danger of catastrophic failure. However, a bad charge pressure signal can affect hydraulic system performance and should be diagnosed before continued heavy use.
What does Bobcat error code M0521 mean?
: M0521 is set by the gateway controller when it detects a short to supply voltage lasting 30 seconds on the hydraulic charge pressure sensor's signal wire (wire 3190 on some models, wire 3420 on others depending on harness variant). The sensor itself runs on an 8.0 volt supply from the gateway controller.
In plain terms, the charge pressure sensor tells the controller how much pressure is present in the hydraulic charge circuit, which helps keep the hydraulic pump supplied and protected. When the signal wire reads a voltage that looks like it is shorted to the supply line, the controller cannot trust the pressure reading anymore and logs M0521.
This is an electrical circuit fault, not necessarily a sign that charge pressure is actually too high. The controller is reporting a wiring or sensor problem that mimics an out-of-range-high condition.
What triggers a Bobcat M0521 code?
The code sets when the gateway controller detects a short to supply voltage for 30 seconds on the hydraulic charge pressure sensor signal wire, with the key switch in the run/enter position.
Common causes of M0521
- 8 volt supply wire (5190 or 3400 depending on harness) shorted to battery voltage or shorted to ground
- Signal wire (3190 or 3420 depending on harness) shorted to supply voltage
- Ground wire (2190 or 3410 depending on harness) open
- Faulty hydraulic charge pressure sensor
- Faulty gateway controller
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, hydraulic charge pressure sensor connector, or mainframe wire harness
- If the code is intermittent and not active during testing, the cause may not be found immediately; likely culprits include loose connections, corrosion, pushed-back pins, the controller, the wire harness, or a combination of these
How to troubleshoot Bobcat M0521: first checks
- With key off, inspect the hydraulic charge pressure sensor connector and the gateway controller connectors for moisture, corrosion, or pushed-back pins
- Trace the 8 volt supply wire (5190 or 3400) for signs of chafing or contact with battery voltage or ground
- Check the signal wire (3190 or 3420) for shorts to the supply voltage wire, especially where harnesses are bundled together or rub against the frame
- Verify the ground wire (2190 or 3410) has continuity and is not open
- If all wiring checks out, test the hydraulic charge pressure sensor output against the expected 8.0 volt supply and swap or bench test if suspect
- If the fault is intermittent, wiggle-test the harness and connectors near the sensor and controller while monitoring for the code to reappear
How the code clears
This code is self resetting. Once the short to supply voltage is repaired and the circuit reads correctly, the code clears on its own without a separate manual clearing procedure.
Affected models and serial ranges
M0521 appears in our records across 16 Bobcat models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| S510 | SN A3NJ11001-99999, SN A3NK11001-99999, SN ATZC11001-ATZC99999 |
| S530 | SN A7TV11001-99999, SN ATZD11001-99999 |
| S550 | SN A3NK11001-A3NL99999, SN A3NM11001-99999 |
| S570 | SN A7U711001-799999, SN A7U811001-899999 |
| S590 | SN ANMN11001-99999, SN ANMP11001-99999 |
| S630 | SN A3NT12370-99999, SN A3NU11001-11111, SN A3NU11112-99999 |
| S650 | SN A3NV11001-13098, SN A3NV13099-99999, SN A3NW11001-11248, SN A3NW11249-99999 |
| S750 | SN A3P211001-299999 |
| S770 | SN A3P411001-99999 |
| T550 | SN A7UJ11001-AJZV12276 |
| T590 | SN ALJU11001-999999, SN B37811001-999999, SN B3Z711001-999999 |
| T630 | SN A7PU11001-11663, SN A7PU11664-99999 |
| T650 | SN A3P012214-099999, SN A3P111242-199999 |
| T750 | SN ANKA11001-A99999 |
| T770 | SN A3P811001-899999, SN A3P911001-999999 |
| T870 | SN A3PG11001-99999, SN A3PH11001-99999 |
Frequently asked questions
What does Bobcat code M0521 mean?
It means the gateway controller detected a short to supply voltage for 30 seconds on the hydraulic charge pressure sensor signal wire, which makes the reading look like an out-of-range-high charge pressure condition.
Is M0521 the same as panel code 05-21?
Yes, 05-21 is the numeric panel display form of M0521.
Do I need to manually clear M0521?
No separate reset procedure is listed for this code. It is self resetting once the underlying short is repaired.
Can I keep operating the machine with M0521 active?
Since this is a sensor circuit fault rather than a confirmed hydraulic overpressure event, short-term operation may be possible, but the hydraulic charge circuit reading is unreliable while the code is active. It is best to diagnose it before continued heavy use.
Which wires are involved in M0521?
Depending on the harness variant, the affected wires are the 8 volt supply (5190 or 3400), the signal wire (3190 or 3420), and the ground wire (2190 or 3410).
Why does M0521 come and go intermittently?
Intermittent faults are often caused by loose connections, corrosion, or pushed-back pins in the connectors rather than a fully failed component. If the code is not active during testing, a thorough wiggle test of the harness and connectors is needed.
What triggers M0521 to set in the first place?
The gateway controller sets the code when it sees the signal wire shorted to supply voltage for 30 seconds while the key switch is in run/enter.