Bobcat M2107 (21-07) Fault Code: Glow Plug Output Open Circuit
Also shown on the panel as 21-07
Glow Plug Output Open Circuit · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Bobcat fault code M2107, shown as 21-07 on the panel, sets when the gateway controller detects an open circuit on wire 8510 to the glow plug relay. It applies with the key switch in the run/enter position and is self resetting once the underlying wiring or relay fault is corrected.
Medium severity. This code affects cold-start glow plug operation rather than engine safety systems directly. It will not stop the machine from running, but it can cause hard starting or no-start conditions in cold weather, so it should be diagnosed before the next cold start rather than ignored.
What does Bobcat error code M2107 mean?
M2107 is set by the gateway controller when it detects an open circuit on wire 8510, the output wire that runs to the glow plug relay. In plain terms, the controller sends a command signal down this wire to energize the glow plug relay for cold starting assistance, and it expects to see a certain electrical condition on that circuit. When the circuit reads open instead, the controller flags M2107.
This is not a code about the glow plugs themselves overheating or failing individually. It is about the control circuit that switches power to the glow plug relay. That means the fault could be in the wiring, the relay, the ground path, or the gateway controller itself, rather than in the glow plugs in the cylinder head.
Because glow plugs assist cold starts, a machine with this code may crank longer or run rough in cold temperatures until it warms up, even though it may otherwise operate normally once running.
Common causes of M2107
- Controller output wire 8510 shorted to supply voltage or open.
- Ground wire open: listed as wire 2115 in some documentation and as wire 2016/2055 in others, depending on model or harness revision.
- A faulty glow plug relay.
- A faulty gateway controller.
- Moisture, corrosion, or pushed back pins in the gateway controller connectors, glow plug relay connectors, or the mainframe harness.
- An intermittent fault that is not present at the time of testing. In this case the cause may not be found immediately, and probable causes include loose connections, corrosion, pushed back pins, the controller, the wire harness, or a combination of these problems.
How to troubleshoot Bobcat M2107: first checks
- Turn the key switch to run/enter as required to set and read the code, and confirm with a diagnostic tool that M2107 is active or stored.
- Visually inspect the gateway controller connectors and the glow plug relay connectors for moisture, corrosion, or pins that have been pushed back out of position.
- Trace and inspect wire 8510 from the gateway controller to the glow plug relay for chafing, breaks, or a short to supply voltage.
- Check the ground wire path (2115 or 2016/2055 depending on model) for continuity and a clean, tight ground connection.
- Test the glow plug relay itself for proper operation, since a failed relay can present the same open-circuit symptom to the controller.
- If the code appears intermittent and is not active during testing, wiggle-test the harness and connectors while monitoring for the fault, since loose connections and pushed back pins often only show up under vibration or movement.
How the code clears
M2107 is listed as self resetting. Once the open circuit is repaired, whether it is the wiring, ground, relay, or a connector issue, the code should clear on its own. No separate manual reset procedure is listed for this code.
Affected models and serial ranges
M2107 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 A3NT10001-12369, 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 M2107 mean?
It means the gateway controller detected an open circuit on wire 8510, the wire that carries the command signal to the glow plug relay. It is an electrical fault in the glow plug control circuit, not a glow plug performance code.
Will M2107 stop my Bobcat from running?
No, this code affects the cold-start glow plug assist circuit rather than core engine operation. However, it can cause hard starting or rough running in cold weather until it is fixed.
Is M2107 the same as fault code 21-07?
Yes, 21-07 is the numeric panel display form of M2107 on affected Bobcat models.
Which Bobcat models can show M2107?
Documented affected models include the S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, and T770 T870.
Why does the ground wire number differ in different manuals for the same code?
Different documentation versions list the ground wire as either 2115 or 2016/2055. This likely reflects different harness revisions or model years, so check your specific machine's wiring diagram to confirm which ground wire applies.
Do I need to manually clear M2107 after repair?
No separate reset procedure is listed. The code is self resetting once the open circuit is repaired.
What if the code shows up intermittently but I can't find the fault?
Intermittent M2107 codes that are not active during testing may not reveal their cause right away. Likely culprits include loose connections, corrosion, pushed back pins, the controller, the wire harness, or a combination of these issues, so a thorough wiggle test of connectors is recommended.