Bobcat M0921 (09-21) Fault Code: Fuel Level Out of Range High
Also shown on the panel as 09-21
Fuel Level Out of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
M0921 (panel code 09-21) sets when the gateway controller detects a short to supply voltage or an open on the fuel level sensor signal wire (3100 or 3180) for 30 seconds. When the code is active, the fuel gauge will peg full regardless of actual fuel level.
Low severity. This is an informational and gauge-accuracy fault, not a machine performance or safety fault. The engine will keep running normally, but you lose an accurate fuel reading, which creates a real risk of running out of fuel unexpectedly. Treat it as a nuisance to fix soon, not an emergency to stop for.
What does Bobcat error code M0921 mean?
M0921 is set by the gateway controller, which supplies 12 volts to the fuel level sensor on wire 3100 or 3180 (depending on model wiring) and watches that circuit for problems. If the controller sees the signal wire shorted to supply voltage, or sees the circuit go open, for 30 seconds, it logs M0921.
The practical symptom is simple: the fuel gauge will peg full. This happens whether or not the tank is actually full, so the gauge can no longer be trusted while the code is active.
This code only reflects a wiring, connector, or sensor problem in the fuel level signal circuit. It does not indicate a fuel system leak, contamination, or engine fueling issue by itself.
What triggers a Bobcat M0921 code?
The gateway controller sets M0921 when it detects a short to supply voltage or an open circuit on the fuel level sensor signal wire (3100 or 3180) that persists for 30 seconds, with the key switch in the run/enter (on) position. No other voltage, temperature, or pressure thresholds are specified.
Common causes of M0921
- Signal wire (3100 or 3180) open or shorted to supply voltage
- Ground wire (3110 or 2180) open
- Fuel level sensor disconnected
- Faulty fuel level sensor
- Faulty gateway controller
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, fuel level sensor connector, fuel harness, or mainframe wire harness
- Intermittent fault: if the code is not active during testing, the cause may not be found at that time, but likely culprits are the same as above, loose connections, corrosion, pushed-back pins, the controller, the harness, or a combination of these
How to troubleshoot Bobcat M0921: first checks
- Turn the key switch to run/enter and confirm the code is present, then check the fuel gauge, it should be pegged full if M0921 is active
- Inspect the fuel level sensor connector for disconnection, moisture, corrosion, or pushed-back pins
- Trace and inspect the signal wire (3100 or 3180) for chafing, an open, or contact with a supply voltage wire
- Check the ground wire (3110 or 2180) for continuity, an open ground will affect the sensor circuit
- Inspect the gateway controller connectors and the mainframe wire harness for corrosion or damaged pins
- If the code is intermittent, wiggle-test connectors and harness sections near the tank and controller while watching for the code to reappear
How the code clears
This code is self resetting. No separate clearing step or reset procedure is listed once the wiring, connector, sensor, or controller issue is repaired.
Affected models and serial ranges
M0921 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 M0921 mean?
It means the gateway controller detected a short to supply voltage or an open circuit on the fuel level sensor signal wire (3100 or 3180) for 30 seconds. While active, the fuel gauge will peg full.
Is it safe to keep operating with M0921 active?
The machine will operate normally since this only affects the fuel level signal circuit. The main risk is that you cannot trust the fuel gauge, so you could run out of fuel without warning. Track fuel by hours or fill-ups until the code is fixed.
Why does my fuel gauge show full when the tank isn't full?
That is the expected symptom of M0921. The gateway controller loses a valid reading on the signal wire and defaults the gauge display to full.
What is the panel display code for M0921?
On the machine display it shows as 09-21.
Does M0921 clear itself after I fix the wiring?
Yes. The code is self resetting once the fault condition, such as an open or shorted wire, disconnected sensor, or corroded connector, is corrected. No manual clearing step is listed.
Which wire numbers are involved in M0921?
Depending on the model and harness, the signal wire is 3100 or 3180, and the related ground wire is 3110 or 2180.
What if the code doesn't show up when I test the machine?
If M0921 is intermittent and not active during testing, the exact cause may not be found right away. Likely causes still include loose connections, corrosion, pushed-back pins, the fuel level sensor, the gateway controller, or the wire harness.