Bobcat M2602 (26-02) Fault Code: Glow Plug Relay Error On
Also shown on the panel as 26-02
Glow Plug Relay Error On · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Bobcat fault code M2602, shown on the panel as 26-02, means the gateway controller detected voltage on the glow plug relay feedback wire (wire 3420 on some models, wire 8550 on others) for 30 seconds when the relay was not commanded on. It points to a stuck relay, a shorted wire, or a controller/connector problem in the glow plug circuit.
Medium severity. This code does not stop the machine from running, but an unwanted glow plug relay signal can mean a stuck relay, a chafed harness, or a controller fault that could worsen or cause hard starting or a drained battery over time. Diagnose it before it leads to a bigger electrical problem.
What does Bobcat error code M2602 mean?
M2602 is set by the gateway controller when it sees voltage on the glow plug relay feedback wire, either wire 3420 or wire 8550 depending on the machine, for 30 seconds while the controller itself did not command the relay on. In plain terms, the controller is watching for a signal that should only appear when it tells the glow plugs to heat, and it is seeing that signal without asking for it.
The glow plug relay controls power to the glow plugs, which preheat the engine's combustion chambers for easier cold starts. If the relay or its wiring is stuck on or shorted to voltage, the controller flags it as an error even if the glow plugs are not currently needed.
This code applies across a wide range of Bobcat skid steer and compact track loader models, including the S510 through S770 and T550 through T870 lines.
What triggers a Bobcat M2602 code?
The code sets when the key switch (run/enter) is on, ambient temperature is above 70°F, and the gateway controller detects voltage on the glow plug relay feedback wire for 30 seconds while the relay is not commanded on.
Common causes of M2602
- Glow plug wire 8500, or the feedback wire (3420 or 8550 depending on model), shorted to supply voltage.
- A stuck or failed glow plug relay.
- A fault in the gateway controller itself.
- Moisture, corrosion, or pushed-back pins in the gateway controller connectors, glow plug relay connectors, or the mainframe harness.
- An intermittent condition from loose connections, corrosion, pushed-back pins, the controller, the wire harness, or a combination of these, which may not be found if the code is not active at the time of testing.
How to troubleshoot Bobcat M2602: first checks
- Confirm the key switch is in the run/enter position and check whether ambient temperature is above 70°F, since these are the conditions under which the code is set.
- Inspect the glow plug relay connector and the gateway controller connectors for moisture, corrosion, or pushed-back pins.
- Check wire 8500 and the feedback wire (3420 or 8550, depending on your model) for signs of chafing or a short to supply voltage.
- Test the glow plug relay itself for a stuck-closed condition or internal failure.
- Inspect the mainframe harness along its run for damage, pinch points, or corrosion that could cause an unintended voltage signal.
- If the code is not active during testing, treat it as intermittent and recheck all connections, since the cause may not be found until the fault reoccurs.
How the code clears
This code is self resetting. No separate clearing step is listed once the repair is complete; once the underlying wiring, relay, or controller issue is fixed, the code should not reset on its own.
Affected models and serial ranges
M2602 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 M2602 mean?
It means the gateway controller detected voltage on the glow plug relay feedback wire for 30 seconds when it had not commanded the relay on. This points to an issue in the glow plug relay circuit, not a general engine failure.
Is M2602 the same as panel code 26-02?
Yes. 26-02 is the numeric panel display form of fault code M2602 on affected Bobcat machines.
Can I keep operating my Bobcat with M2602 active?
The code itself does not disable the machine, but it signals a possible stuck relay or wiring short. Since this is electrical and could affect cold starting or drain the battery over time, it should be diagnosed rather than ignored.
Why does ambient temperature matter for this code?
The conditions for setting M2602 include ambient temperature above 70°F. At that temperature glow plugs are not normally needed, so any relay feedback voltage detected under these conditions is treated as unexpected and flags the error.
Does M2602 clear itself after I fix the problem?
The code is listed as self resetting. No separate manual clearing procedure is documented, but the underlying wiring, relay, or controller issue must be repaired or the code can return.
Which wire is affected, 3420 or 8550?
It depends on the machine's wiring configuration. Some models use feedback wire 3420 and others use feedback wire 8550. Both wires perform the same glow plug relay feedback function, and either can trigger M2602 if shorted to supply voltage.
What if the code shows up only sometimes?
Intermittent M2602 codes are common with loose connections, corrosion, or pushed-back pins. If the fault is not active during testing, the exact cause may not be identifiable until it reoccurs, so a thorough inspection of all related connectors and harness sections is still worthwhile.