Bobcat M3506 (35-06) Fault Code: Hydraulic Fan Solenoid Error Off
Also shown on the panel as 35-06 · Also called Hydraulic Fan Short to Ground
Hydraulic Fan Solenoid Error Off · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Bobcat code M3506 (panel form 35-06) sets when the gateway controller commands the hydraulic fan solenoid but does not detect voltage on signal wire 4010 or return wire 2910. When this code is active, the hydraulic fan runs at full speed as a fail-safe.
Medium severity. The machine keeps running and the hydraulic fan defaults to full speed, so there is no immediate shutdown risk, but constant full-speed fan operation increases wear and can mask a wiring or solenoid fault that should be fixed before it causes cooling problems or an electrical short elsewhere.
What does Bobcat error code M3506 mean?
M3506 is a Bobcat gateway controller code tied to the hydraulic fan solenoid circuit. The gateway controller normally turns the hydraulic fan solenoid on or off based on engine temperature or hydraulic temperature. It does this by commanding the solenoid through signal wire 4010 and return wire 2910.
When the controller sends the command but does not see the voltage it expects on those wires, it logs M3506. Because the controller can no longer trust or control the fan circuit normally, it defaults the hydraulic fan to run at full speed so the machine does not overheat while the fault is present.
This code affects the S510, S530, S550, S570, S590, S630, S650, S750, S770 skid-steer loaders and the T550, T590, T630, T650, T750, T770, T870 compact track loaders.
Common causes of M3506
- Controller output wire 4010 or return wire 2910 shorted to ground.
- Faulty hydraulic fan solenoid.
- Fault within the gateway controller itself.
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, the hydraulic fan solenoid connector, or the mainframe harness.
- Intermittent condition: if the code is not active at the time of testing, the root cause may not be found right away. Probable causes in that case include loose connections, corrosion, pushed-back pins, the controller, the wire harness, or a combination of these.
How to troubleshoot Bobcat M3506: first checks
- With the key switch on (run/enter) and during engine cranking, check for voltage on signal wire 4010 and return wire 2910 at the hydraulic fan solenoid connector and trace back to the gateway controller connector.
- Inspect the gateway controller connectors and the hydraulic fan solenoid connector for moisture, corrosion, or pins that have been pushed back out of position.
- Inspect the mainframe harness along the run to the hydraulic fan solenoid for chafing, pinch points, or exposed wire that could be shorting wire 4010 or 2910 to ground.
- Test the hydraulic fan solenoid itself for proper operation, since a failed solenoid can cause the controller to see an unexpected voltage state.
- If the code is not currently active, treat it as intermittent and recheck all connectors, terminals, and harness routing since loose connections and corrosion are the most likely repeat offenders.
How the code clears
Bobcat lists the clearing step as cycling the key power off and back on once the repair is complete. There is no separate reset procedure listed beyond a power cycle.
Affected models and serial ranges
M3506 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 M3506 mean?
It means the gateway controller commanded the hydraulic fan solenoid on or off but did not detect the voltage it expected on signal wire 4010 or return wire 2910. This points to a wiring, connector, solenoid, or controller problem in that circuit.
Is it safe to keep operating with M3506 active?
The machine will keep running and the hydraulic fan defaults to full speed as a safeguard, so it is not an immediate stop-work situation. However, the underlying wiring or solenoid fault should be diagnosed and repaired promptly since running the fan at full speed all the time is not normal operation.
Why does the hydraulic fan run at full speed when this code is set?
The gateway controller cannot verify or control the fan solenoid circuit correctly, so it defaults to full-speed fan operation as a fail-safe to prevent overheating while the fault is present.
What wires are involved in code M3506?
The code involves the hydraulic fan solenoid signal wire 4010 and return wire 2910, along with the connectors and mainframe harness that carry those wires between the gateway controller and the solenoid.
What if the code does not show up when I test the machine?
That means the fault is intermittent. Bobcat notes the cause may not be found right away in these cases, and the likely culprits are loose connections, corrosion, pushed-back pins, the controller, or the wire harness, or some combination of these.
How do I clear code M3506 after repair?
Cycle the key power off and back on. No other reset procedure is listed for this code.
Which Bobcat models can set M3506?
It applies to the S510, S530, S550, S570, S590, S630, S650, S750, S770 skid-steer loaders and the T550, T590, T630, T650, T750, T770, T870 compact track loaders.