Bobcat D7577 (75-77) Fault Code: Left Speed Sensor Out of Range High
Also shown on the panel as 75-77 · Also called Drive Left Speed Sensor Out of Range High, Left Speed Sensor Out Of Range High
Left Speed Sensor Out of Range High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
D7577 (panel code 75-77) sets when the drive controller sees pulses from the left speed sensor above 4.85 volts. The machine drops into speed management mode until the issue is fixed. It affects the wiring, sensor, or drive controller on the left side of the drive system.
Medium severity. The machine keeps running but is limited to speed management mode, which reduces performance and can mask real handling problems. Not an immediate shutdown risk, but should be diagnosed before continued heavy use.
What does Bobcat error code D7577 mean?
D7577 is set by the drive controller when it reads pulses from the left speed sensor at a voltage greater than 4.85 volts, which is outside the expected range. The controller uses this sensor's signal to know how fast and whether the machine is actually moving on the left side.
On a wheel machine, the left speed sensor sits in the motor carrier and reads magnets on a rotating disk. On a track machine, the sensor is in the drive motor and reads teeth on a metal sprocket as it turns. Either way, the signal tells the controller real-world wheel or track speed so it can manage power and prevent runaway or mismatched drive behavior.
When this code is active, the machine automatically switches to speed management mode, a reduced or protected operating mode, until the fault clears or is repaired. This is the controller's way of continuing to operate safely without trusting a speed signal it can't verify.
What triggers a Bobcat D7577 code?
Key switch (run/enter) must be on for the controller to detect and set this code, and it sets when the left speed sensor signal is read above 4.85 volts.
Common causes of D7577
- Signal wire (3020, 3880, 3080, or 3885 depending on model/harness) shorted to supply voltage
- 5 volt supply wire (1540 or 5880 depending on model/harness) shorted to supply voltage
- Ground wire (2580 or 2880 depending on model/harness) open
- Faulty left wheel speed sensor
- Faulty drive controller
- Moisture, corrosion, or pushed-back pins in the drive controller connectors or SJC harness connectors
- Intermittent causes that may not show up during testing if the code isn't active: loose connections, corrosion, pushed-back pins, a marginal controller, harness damage, or a combination of these
How to troubleshoot Bobcat D7577: first checks
- Confirm the code is currently active or check history to see if it's intermittent, since intermittent faults may not reproduce during a static check
- Inspect the drive controller connectors and SJC harness connectors for moisture, corrosion, or pins that have pushed back out of their sockets
- Check the signal wire (3020/3880 or 3080/3885 depending on model) for a short to supply voltage
- Check the 5 volt supply wire (1540 or 5880 depending on model) for a short to supply voltage
- Check the ground wire (2580 or 2880 depending on model) for an open circuit
- Inspect the left wheel speed sensor itself for damage, debris, or incorrect air gap on the rotating disk or sprocket
- If wiring and sensor check out, suspect the drive controller
How the code clears
This code is self resetting. Once the underlying wiring, sensor, or controller issue is repaired, the code clears on its own without a separate manual reset procedure.
Affected models and serial ranges
D7577 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 |
| 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 D7577 mean?
It means the drive controller detected the left speed sensor signal reading above 4.85 volts, which is outside the normal range. The controller responds by putting the machine into speed management mode until the issue is resolved.
Is D7577 the same as panel code 75-77?
Yes. 75-77 is the numeric panel display form of fault code D7577 on Bobcat machines.
Can I keep operating with D7577 active?
The machine will still run but only in speed management mode, which limits performance. It's best treated as a diagnose-soon issue rather than something to ignore, since the controller can't fully trust the left speed signal while it's active.
Do I need to manually clear this code?
No. This code is self resetting. Once the wiring, sensor, or controller problem is fixed, the code clears on its own with no separate reset procedure needed.
Which Bobcat models can show D7577?
This code applies to S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, T770, and T870 models.
What's the difference between a wheel machine and track machine sensor for this code?
On wheel machines, the left speed sensor is in the motor carrier and reads magnets on a rotating disk. On track machines, the sensor is in the drive motor and reads teeth on a metal sprocket. Both feed the same type of speed signal to the drive controller.
Why does an intermittent code matter if it's not active right now?
If the code isn't on during testing, the root cause, such as a loose connection, corrosion, a pushed-back pin, or a marginal wire harness or controller, may not be found immediately. It's worth a thorough connector inspection even if the fault isn't currently showing.