Bobcat M4721 (47-21) Fault Code: 8 Volt Sensor Supply Out of Range High
Also shown on the panel as 47-21
8 Volt Sensor Supply Out of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
M4721 (panel code 47-21) sets when the gateway controller sees the 8 volt sensor supply, on wire 5190 or wire 3400 depending on model, go above 8.9 volts for 5 seconds. This supply feeds the hydraulic charge pressure sensor, engine coolant temperature sensor, and hydraulic oil temperature sensor, so the fault can affect readings from all three at once.
Medium severity. This is a sensor supply voltage fault, not a direct engine or hydraulic shutdown code. It can cause inaccurate readings from three sensors at once, so it should be diagnosed within the shift rather than ignored, especially before relying on coolant or hydraulic oil temperature gauges.
What does Bobcat error code M4721 mean?
>The M4721 code means the gateway controller has detected that its own 8 volt reference supply is reading higher than it should be. Instead of holding steady near 8 volts, the supply has climbed above 8.9 volts and stayed there for 5 seconds, which is long enough for the controller to flag it as a real fault rather than a brief glitch.
This 8 volt supply is not just for one sensor. It powers the hydraulic charge pressure sensor, the engine coolant temperature sensor, and the hydraulic oil temperature sensor. Because all three sensors share this supply, a high-voltage fault on it can throw off multiple readings at the same time, which is why this code deserves attention even if the machine seems to be running normally.
Depending on the machine's wiring configuration, the affected wire is either 5190 or 3400. Both versions of the fault work the same way and use the same threshold and timing.
What triggers a Bobcat M4721 code?
The gateway controller sets M4721 when it detects the 8 volt sensor supply (wire 5190 or wire 3400) reading above 8.9 volts for 5 seconds, with the key switch in the run/enter position.
Common causes of M4721
- The 8 volt supply wire (5190 or 3400 depending on model) is shorted to battery voltage somewhere in the harness.
- A fault in the gateway controller itself.
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, the hydraulic charge pressure sensor connector, or the mainframe harness connectors.
- An intermittent condition where the code is not active at the time of testing. In this case the cause may be pushed-back pins, the controller, the wire harness, or a combination of these problems, making it harder to pin down on a single check.
How to troubleshoot Bobcat M4721: first checks
- >Check the wiring for the 8 volt supply wire (5190 or 3400) for chafing, pinching, or contact with battery-voltage wiring that could cause a short.
- Inspect the gateway controller connectors for moisture, corrosion, or pins that have been pushed back out of their sockets.
- Inspect the hydraulic charge pressure sensor connector for the same issues: moisture, corrosion, or pushed-back pins.
- Inspect the mainframe harness connectors along the run of wire 5190 or 3400 for damage or poor connections.
- If the code is not active when you test, treat it as intermittent and recheck all connectors and harness sections listed above rather than assuming a clean bill of health.
- If wiring and connectors check out, consider the gateway controller itself as a possible cause.
How the code clears
This code is self resetting. Once the underlying wiring or connector issue is repaired and the 8 volt supply reads within range again, the code should clear on its own without a separate manual reset procedure.
Affected models and serial ranges
M4721 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 M4721 mean?
It means the gateway controller detected the 8 volt sensor supply voltage (on wire 5190 or wire 3400 depending on the machine) reading above 8.9 volts for 5 seconds. This supply feeds the hydraulic charge pressure sensor, engine coolant temperature sensor, and hydraulic oil temperature sensor.
Is M4721 the same as panel code 47-21?
Yes. 47-21 is the numeric panel form of fault code M4721 on Bobcat equipment.
Which sensors does M4721 affect?
The 8 volt supply involved in this code powers three sensors: the hydraulic charge pressure sensor, the engine coolant temperature sensor, and the hydraulic oil temperature sensor. A fault here can affect readings from all three.
Do I need to manually clear M4721 after repair?
No separate reset procedure is listed for this code. It is self resetting, meaning it should clear on its own once the 8 volt supply voltage returns to normal range.
Can M4721 be an intermittent fault?
Yes. If the code is not active at the time of testing, the cause may still be pushed-back pins, a controller issue, harness wiring, or a combination of these, so intermittent behavior does not mean the problem is gone.
Which Bobcat models can show code M4721?
This code applies to a range of Bobcat skid-steer and track loader models, including the S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, and T770 lines.
What usually causes the 8 volt supply to read too high?
The most common causes are the 8 volt supply wire being shorted to battery voltage, moisture or corrosion in the gateway controller or hydraulic charge pressure sensor connectors, pushed-back pins in those connectors or the mainframe harness, or in some cases a fault in the gateway controller itself.