Bobcat M4803 (48-03) Fault Code: Front Light Relay Error Off
Also shown on the panel as 48-03
Front Light Relay Error Off · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Bobcat fault code M4803, panel form 48-03, sets when the gateway controller commands the front work lights on but does not detect voltage feedback on wire 3460 (or wire 6330 on some models). It points to a front light circuit problem: a blown fuse, an open supply wire, a bad relay, or a wiring or connector fault, not a serious drivetrain or hydraulic issue.
Low severity. M4803 affects the front work lights only. It does not disable the machine or threaten engine, hydraulic, or structural safety. Fix it when convenient, but keep in mind reduced front lighting can be a real visibility and jobsite safety issue at night or in low light.
What does Bobcat error code M4803 mean?
M4803 is a front light relay error. The gateway controller sends a command to turn on the front work lights and then checks for a feedback voltage signal on a specific wire, either wire 3460 or wire 6330 depending on the machine and harness variant, to confirm the relay actually switched on. If that feedback voltage never shows up, the controller logs M4803.
This is strictly a feedback and confirmation circuit issue. The controller is not seeing what it expects to see, which usually means power is not getting to the relay, the relay itself is not switching, or the feedback wire has an open or short somewhere between the relay and the controller.
Because this only affects the front work light circuit, the machine will typically still drive, lift, and operate normally. The practical downside is you may be working without functional front lights, which matters for safety during early morning, evening, or indoor jobs.
Common causes of M4803
- FRC1 fuse (referred to as fuse 2 or fuse 10 depending on the specific harness/model documentation) blown or not making contact
- Supply wire 1330 open, cutting power to the front light relay circuit
- Controller feedback wire (3460 or 6330 depending on variant) shorted to ground or open
- Front work light wires 6100 or 6310 shorted to ground
- Faulty front work lights relay that fails to switch or confirm state
- Faulty gateway controller
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, front light relay connectors, tailgate connector, cab harness, tailgate harness, or mainframe harness
- Intermittent fault: if the code is not active at the time of testing, the cause may not be found right away; loose connections, corrosion, pushed-back pins, the controller, or the wire harness (or a combination) remain the likely suspects
How to troubleshoot Bobcat M4803: first checks
- Turn the key switch to run/enter and enable the front work lights, then confirm the fault is active before chasing wiring, since this code depends on that specific condition
- Check FRC1 fuse (documented as fuse 2 on some models, fuse 10 on others) for continuity and a solid seat in its holder
- Inspect supply wire 1330 for continuity from its source to the front light relay, looking for an open circuit
- Check the front work light wires 6100 and 6310 for shorts to ground, especially near the tailgate and mainframe harness routing
- Test the front work lights relay itself, checking that it switches correctly and is not stuck or damaged
- Inspect the controller feedback wire (3460 or 6330 depending on your model's wiring) for opens or shorts to ground between the relay and the gateway controller
- Open and inspect the gateway controller connectors, front light relay connectors, tailgate connector, cab harness, tailgate harness, and mainframe harness connectors for moisture, corrosion, or pushed-back pins
- If the code will not stay active for testing, treat it as intermittent and focus on connector conditions, loose terminals, and harness rub points rather than assuming a single failed part
How the code clears
Once the repair is complete, cycle power to clear the M4803 code. No separate clearing step is listed beyond a power cycle.
Affected models and serial ranges
M4803 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 M4803 mean?
It means the gateway controller commanded the front work lights on but did not detect the expected feedback voltage on wire 3460 or wire 6330 (depending on your machine's wiring), so it flagged a front light relay error.
Is M4803 dangerous to keep driving with?
No, it is limited to the front work light circuit and does not affect steering, braking, hydraulics, or engine operation. The main concern is reduced visibility if you rely on the front work lights.
Why does my Bobcat throw M4803 only sometimes?
Intermittent M4803 codes are usually caused by loose connections, corrosion, or pushed-back pins in the connectors rather than a fully failed part. If the code is not active when you test, you may need to wiggle-test harnesses and connectors to reproduce it.
Which fuse should I check first for M4803?
Check the FRC1 fuse, documented as fuse 2 on some models and fuse 10 on others depending on your machine's wiring variant. Confirm it has continuity and is seated firmly.
How do I clear M4803 after fixing it?
Cycle the key/power off and back on. No separate reset procedure is listed for this code beyond a power cycle.
Do I need a diagnostic tool to fix M4803?
A tool helps confirm the code and its variant (3460 vs 6330 feedback wire), but the actual repair is basic electrical diagnosis: check the fuse, supply wire, relay, feedback wire, and connectors for corrosion or damage.