Bobcat D7579 (75-79) Fault Code: Left Speed Sensor Out of Range Low
Also shown on the panel as 75-79 · Also called Drive Left Speed Sensor Out of Range Low, Left Speed Sensor Out Of Range Low
Left Speed Sensor Out of Range Low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Bobcat code D7579 (panel display 75-79) means the drive controller is reading pulses from the left speed sensor below 0.15 volts, which is too low for it to trust for machine movement and speed data. The machine will drop into speed management mode until the fault is resolved.
Medium severity. D7579 does not shut the machine down, but it forces speed management mode, which limits normal drive performance. It should be diagnosed before returning the machine to full production work, since a lost speed signal affects how the controller manages travel.
What does Bobcat error code D7579 mean?
D7579 sets when the drive controller detects that the pulse signal coming from the left speed sensor is less than 0.15 volts. The controller uses this pulse signal to know how fast, and whether, the machine is moving on the left side drive.
On wheeled machines, the left speed sensor reads magnets on a rotating disk inside the motor carrier. On track machines, the sensor reads the teeth on a metal sprocket inside the drive motor. Either way, if the controller sees a signal that stays under the 0.15 volt threshold, it assumes the sensor input is unreliable.
When this happens, the machine does not shut down, but it switches to speed management mode as a protective measure, meaning drive performance is limited until the fault clears or is repaired.
Common causes of D7579
- Signal wire shorted to ground. Depending on model and wiring revision, this is signal wire 3080, 3885, 3020, or 3880.
- 5 volt supply wire shorted to ground or open. Depending on model and wiring revision, this is wire 1540 or 5880.
- A faulty left wheel speed sensor.
- A faulty drive controller.
- Moisture, corrosion, or pushed-back pins in the drive controller connectors or SJC harness connectors.
- Intermittent faults: if the code is not active at the time of testing, the root cause may not be found right away. Likely culprits include loose connections, corrosion, pushed-back pins, the controller itself, the wire harness, or some combination of these.
How to troubleshoot Bobcat D7579: first checks
- Confirm the key switch is in the run/enter position, since this is the condition under which the code sets.
- Inspect the drive controller connectors and SJC harness connectors for moisture, corrosion, or pins that have pushed back out of their sockets.
- Check the left wheel speed sensor wiring and connector for damage, chafing, or a poor seat.
- Test the signal wire (3080, 3885, 3020, or 3880 depending on your machine) for a short to ground.
- Test the 5 volt supply wire (1540 or 5880 depending on your machine) for a short to ground or an open circuit.
- If no fault is found and the code is intermittent, recheck all connections under load and vibration, since intermittent faults often trace back to loose or corroded connectors rather than a failed component.
- If wiring and connectors check out, test the left wheel speed sensor itself, then suspect the drive controller as a last step.
How the code clears
D7579 is self resetting. There is no separate manual clearing procedure listed for this code. Once the wiring, sensor, or connector issue causing the low voltage signal is repaired, the code should clear on its own as the controller sees a valid pulse signal again.
Affected models and serial ranges
D7579 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 D7579 mean?
It means the drive controller is seeing a left speed sensor signal below 0.15 volts, which is too low to use reliably for tracking machine speed and movement. The machine responds by running in speed management mode.
Can I keep operating the machine with D7579 active?
The machine will still move, but it operates in speed management mode with limited drive performance. It is best to diagnose the cause before continuing normal work, since the controller is not getting a trustworthy speed signal from the left side.
Do I need a scan tool to clear D7579?
No. The code is self resetting once the underlying wiring, connector, or sensor problem is fixed. There is no separate manual reset step.
Which wires should I check first for D7579?
Check the signal wire feeding the left speed sensor (labeled 3080, 3885, 3020, or 3880 depending on your model and harness) for a short to ground, and the 5 volt supply wire (1540 or 5880 depending on model) for a short to ground or an open.
Why does D7579 come and go instead of staying on?
Intermittent behavior usually points to loose connections, corrosion, or pushed-back pins in the drive controller or SJC harness connectors. These faults may not show up unless the machine is vibrating or the connector is disturbed, which can make the cause hard to pin down on a static test.
Is the left speed sensor different on wheeled and tracked Bobcat machines?
Yes. On wheeled machines, the sensor is in the motor carrier and reads magnets on a rotating disk. On tracked machines, the sensor is in the drive motor and reads the teeth on a metal sprocket. Both feed the same type of pulse signal to the drive controller.
Which Bobcat models can show D7579?
This code applies across a range of loader models including the S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, T770, and T870.