Bobcat H3128 (31-28) Fault Code: Interrupted Power Failure
Also shown on the panel as 31-28
Interrupted Power Failure · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
H3128 (panel code 31-28) means the auxiliary controller, or on some machines the deluxe MX controller, unexpectedly lost battery power after the system was already powered up. It is a stored-only code, meaning it never displays live to the operator, it only shows up when a technician pulls stored fault history with the key switch or run/enter switch on.
Medium severity. H3128 does not disable the machine outright since it is a stored code only, but an unexpected power interruption to a controller can point to a fuse, wiring, or grounding fault that may cause other intermittent electrical problems or controller dropouts. It should be diagnosed before it leads to repeated no-start or control module resets.
What does Bobcat error code H3128 mean?
H3128 sets when the auxiliary controller (or, on machines equipped with it, the deluxe MX controller) briefly or fully loses its battery power supply after the machine has already completed power-up. Since the code is stored only, the operator never sees an active warning for it. It shows up later when a technician connects a diagnostic tool and reviews stored fault codes.
This code is really a symptom of a power delivery problem somewhere in that controller's circuit, not a failure of a specific sensor or actuator. The controller itself detected that its own power input dropped out or interrupted while it should have stayed on.
Because the auxiliary and deluxe MX controllers often manage secondary functions, an interrupted power event can cause those functions to reset, hesitate, or temporarily stop responding, even if the operator never noticed a visible fault light.
Common causes of H3128
- Blown or failing fuse: depending on the machine and controller variant, this is FRC1 fuse 4, FRC1 fuse 6, FC1 fuse 2, or fuse 4/fuse 6 on deluxe MX-equipped machines.
- Supply wire 1150, 1170, or 1180 shorted to ground or open (wire number depends on controller variant).
- Switched power wire 1560 or 1700 shorted to ground or open (wire number depends on controller variant).
- Ground wire 2540, 2550, 2730, or 2740 open (wire number depends on controller variant).
- A fault in the auxiliary controller or deluxe MX controller itself.
- Moisture, corrosion, or pushed-back pins in the controller connectors, control harness, power harness, or mainframe harness.
- Intermittent causes that may not be found if the code is not active at the time of testing: loose connections, corrosion, pushed-back pins, a controller fault, a harness fault, or a combination of these.
How to troubleshoot Bobcat H3128: first checks
- Turn the key switch or run/enter switch on and pull stored codes with the diagnostic tool to confirm H3128 is present and check for related active codes.
- Inspect the relevant fuse for the machine's controller type (FRC1 fuse 4, FRC1 fuse 6, or FC1 fuse 2 for auxiliary controllers; fuse 4 or fuse 6 for deluxe MX controllers) for continuity and secure seating in the fuse block.
- Visually inspect the auxiliary controller or deluxe MX controller connectors, and the mainframe harness connectors, for moisture, corrosion, or pins that have pushed back out of their sockets.
- Check supply wire (1150, 1170, or 1180) and switched power wire (1560 or 1700) for chafing, shorts to ground, or open circuits along their length.
- Check ground wire (2540, 2550, 2730, or 2740) for continuity and a clean, tight ground connection.
- If the code does not reappear during testing, treat it as intermittent and focus on loose connections, corrosion, and pushed-back pins since these are the most common repeat offenders.
How the code clears
No separate clearing step is listed for this code. It is a stored-only code, so once the underlying wiring, fuse, or connector issue is repaired, it will not reset on its own until the same power interruption condition happens again. Clear stored codes with the diagnostic tool after repairs and run the machine to confirm it does not return.
Affected models and serial ranges
H3128 appears in our records across 18 Bobcat models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| E35 | SN A93K110001-99999, SN AC2P11001-99999 |
| E45 | SN AHHC11001-99999 |
| S510 | SN A3NJ11001-99999, SN A3NK11001-99999, SN ATZC11001-99999 |
| 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 A39511001-99999, 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 H3128 mean?
It means the auxiliary controller, or on some machines the deluxe MX controller, lost battery power unexpectedly after the machine had already powered up. It's stored in fault history and does not display live to the operator.
Why don't I see H3128 on my Bobcat display while operating?
H3128 is a stored-only code. It only appears when a technician retrieves stored fault codes with a diagnostic tool with the key switch or run/enter switch on. It was never designed to alert the operator in real time.
Which fuse should I check first for H3128?
It depends on your machine's controller setup. Auxiliary controller machines may point to FRC1 fuse 4, FRC1 fuse 6, or FC1 fuse 2. Machines with the deluxe MX controller may point to fuse 4 or fuse 6. Check the fuse listed for your specific controller variant.
Is H3128 dangerous to keep operating with?
It's not an immediate safety shutdown since it's a stored code, but an interrupted power supply to a controller suggests a wiring, fuse, or grounding issue that could cause intermittent electrical problems elsewhere. It's worth diagnosing promptly rather than ignoring it.
Why does H3128 come back even after I check everything and find nothing wrong?
This is common with intermittent power interruptions. If the code isn't active during testing, the cause may be loose connections, corrosion, or pushed-back pins that only cause a problem under vibration, temperature change, or specific conditions. Keep an eye on connector condition over time.
Does H3128 clear itself after a repair?
No separate clearing step is listed for this code. After repairing the wiring, fuse, or connector issue, clear the stored code with a diagnostic tool and run the machine to verify it doesn't return.
Which Bobcat machines can show code H3128?
H3128 applies across a range of Bobcat excavators, skid-steers, and track loaders including the E35, E45, S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, and T770 models.