Bobcat M5107 (51-07) Fault Code: Rear Light Output Open Circuit
Also shown on the panel as 51-07
Rear Light Output Open Circuit · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
M5107, panel code 51-07, sets when the gateway controller detects an open circuit on the rear light relay signal wire 6210. The controller sends battery voltage on wire 6210 to the rear light relay whenever the lights are commanded on, and if that circuit doesn't complete, the code sets.
Low severity. This code affects rear lighting output only. It does not indicate an engine, hydraulic, or drivetrain problem, but running without working rear lights is a real safety and legal issue, especially at night, in low visibility, or on public roads. Diagnose it before the next shift that requires lighting.
What does Bobcat error code M5107 mean?
A code M5107 occurs when the gateway controller detects an open on the rear light relay signal wire 6210. Normally, when the operator commands the lights on, the gateway controller sends battery voltage down wire 6210 to the rear light relay to energize it and turn on the rear lights. If the controller doesn't see that circuit complete the way it expects, it logs M5107 as an open circuit fault.
This is strictly an output-circuit fault on the rear lighting system. It does not affect engine performance, hydraulics, or machine controls. The main risk is operating with no rear lights, which is a safety and visibility hazard rather than a mechanical one.
Depending on the machine and harness variant, the return path for this circuit is ground wire 2010 on some models and ground wire 2055 on others. Either way, the fault logic is the same: the gateway controller expects a complete circuit through the rear light relay and flags it when that circuit is open.
Common causes of M5107
- Signal wire 6210 open, or the ground return wire open (ground wire 2010 on some models, ground wire 2055 on others depending on harness variant)
- Faulty rear light relay
- Faulty gateway controller
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, rear light relay connector, or the mainframe harness
- Loose connections or a combination of wiring, connector, and controller issues, especially if the code is intermittent and not present at the time of testing
How to troubleshoot Bobcat M5107: first checks
- Confirm the code is present with the key switch in run/enter position, since that is the condition under which the gateway controller monitors this circuit
- Inspect the rear light relay connector and gateway controller connectors for moisture, corrosion, or pins that have been pushed back out of place
- Check signal wire 6210 for continuity and for any chafe points, cuts, or loose terminals along the mainframe harness
- Check the ground return wire (2010 or 2055 depending on the machine) for a solid, clean ground connection
- Test the rear light relay itself for proper function, since a failed relay will present the same open-circuit symptom
- If the code is not currently active but was logged previously, treat it as intermittent and focus on loose connections, corrosion, and pushed-back pins as the most likely repeat offenders
How the code clears
Once the repair is complete, clear the code by cycling power (turning the key switch off and back on). No separate reset procedure is listed for this code beyond a power cycle.
Affected models and serial ranges
M5107 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 M5107 mean?
It means the gateway controller detected an open circuit on the rear light relay signal wire 6210. The controller sends battery voltage on that wire to the rear light relay whenever the lights are commanded on, and this code sets when that circuit doesn't complete as expected.
Is M5107 a serious fault?
It's low severity mechanically since it only affects rear lighting output, but it's a real safety concern if you need rear lights and they aren't working, especially at night or on roadways. Get it fixed before operating in low light.
What is the panel display code for M5107?
On the dash panel, this fault shows as 51-07.
Which Bobcat models can show M5107?
This code applies to S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, T770, and T870 models.
How do I clear M5107 after fixing the wiring or relay?
Cycle power by turning the key switch off and back on. That's the only clearing step listed for this code.
Why does M5107 come and go instead of staying on?
Intermittent M5107 codes are usually caused by loose connections, corrosion, or pushed-back pins in the connectors rather than a fully broken wire. These issues can make and break contact as the machine vibrates or heats up, so the fault may not be present when you test it.
Is the ground wire for M5107 the same on every machine?
No. Depending on the specific model and harness variant, the ground return for this circuit is either wire 2010 or wire 2055. Check both the signal wire 6210 and whichever ground wire applies to your machine.