DiagnosticsMedium severity

Bobcat M4404 (44-04) Fault Code: Auxiliary Controller No Communication

Also shown on the panel as 44-04 · Also called Auxiliary No Communication

Auxiliary Controller No Communication · ai-assisted, editor-reviewed · Last updated 2026-07-13

TL;DR

Bobcat code M4404 (panel form 44-04) means the gateway controller has lost CAN communication with the auxiliary controller. It sets whenever the key switch (run/enter) is on and the gateway can't talk to the auxiliary controller. This affects a wide range of Bobcat skid steer and compact track loader models including the S510 through S770 and T550 through T870 series.

Medium severity. M4404 is a communication fault, not an immediate mechanical failure, but it can disable functions controlled by the auxiliary controller until fixed. Diagnose it before returning the machine to full work duty, especially if other CAN codes are present at the same time.

What does Bobcat error code M4404 mean?

M4404 fires when the gateway controller, which acts as the central communication hub on the machine, stops receiving CAN bus messages from the auxiliary controller. CAN (Controller Area Network) is the wiring network that lets the machine's various controllers talk to each other. If that link drops, the gateway can't get status or command information from the auxiliary controller, and functions tied to it may not work correctly.

This code is listed for a wide range of Bobcat loader models, and it appears across several documentation variants (labeled A and B in Bobcat service literature) with only minor differences in the fuse numbers cited. The underlying meaning is the same: a break somewhere in the power, ground, or data path between the gateway and auxiliary controllers.

Common causes of M4404

Other CAN communication codes present at the same time, which can point to a bus-wide problem rather than an isolated wiring fault
CAN communication wire 9120 or 9220 open
Supply wire 1150 or 1180 shorted to ground or open
Ground wire 2540 or 2550 open
Switched power wire 1560 open
A blown fuse: depending on the machine variant this is FC1 fuse 2, FC1 fuse 4, FRC1 fuse 4, FRC1 fuse 6, fuse 4, or fuse 6
A failed auxiliary controller
A failed gateway controller
Moisture, corrosion, or pushed-back pins in the gateway controller connectors, the auxiliary controller connectors, or the mainframe harness
An intermittent fault that is not active at the time of testing, which can be caused by loose connections, corrosion, pushed-back pins, a marginal controller, harness damage, or a combination of these

How to troubleshoot Bobcat M4404: first checks

Turn the key switch to run/enter and check whether M4404 is active now or was only stored, since intermittent faults may not be present during testing
Check for other CAN communication codes logged at the same time, since a shared wiring or bus problem can trigger multiple codes together
Inspect the fuses listed for your machine variant (FC1 fuse 2, FC1 fuse 4, FRC1 fuse 4, FRC1 fuse 6, fuse 4, or fuse 6) for continuity and correct seating
Visually inspect the gateway controller and auxiliary controller connectors and the mainframe harness for moisture, corrosion, or pushed-back pins
Check switched power wire 1560, supply wires 1150/1180, and ground wires 2540/2550 for opens or shorts to ground using a meter with the harness disconnected from the controllers
Trace CAN communication wires 9120 and 9220 for continuity end to end, looking for chafe points, pinches, or connector damage along the mainframe harness
If no fault is found and the code was intermittent, wiggle-test connectors and harness sections near the gateway and auxiliary controllers while monitoring for the code to reset

How the code clears

Bobcat's documented clearing step for M4404 across every variant is the same: cycle the key power off and back on after the repair is complete. No separate reset procedure or scan tool clear step is listed beyond a power cycle.

Affected models and serial ranges

M4404 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

Safety-critical: confirm before use

Electrical safety: stop the engine before inspecting wiring, fuses, connectors, or drive belts, and avoid shorting power terminals. Thresholds, component locations, wire numbers, fuse locations, and reset procedures can vary by model, configuration, and serial number. Confirm them in the service documentation for your exact machine.

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Frequently asked questions

What does Bobcat code M4404 mean?

It means the gateway controller cannot communicate over CAN with the auxiliary controller. It's a communication fault between two of the machine's control modules, not a specific sensor or component failure by itself.

What is the panel display code for M4404?

On machines that show numeric panel codes, M4404 displays as 44-04.

Which Bobcat models can show code M4404?

It's listed for the S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, T770, and T870.

Can a blown fuse cause M4404?

Yes. Depending on the machine, the relevant fuse is FC1 fuse 2, FC1 fuse 4, FRC1 fuse 4, FRC1 fuse 6, fuse 4, or fuse 6. Checking these is one of the fastest first steps.

Why does M4404 come and go instead of staying on?

If the fault is intermittent, Bobcat notes the cause may not be found during testing. Likely culprits are loose connections, corrosion, pushed-back pins, a marginal controller, or harness wear, sometimes in combination.

How do you clear M4404 after repair?

Cycle the key power off and back on. That is the only clearing step listed for this code.

Does M4404 mean the auxiliary controller itself is bad?

It could be, but Bobcat lists the auxiliary controller and gateway controller as just two of several possible causes alongside wiring, fuses, and connector corrosion. Wiring and connectors should be ruled out first since they are more common and cheaper to fix.