Bobcat D7591 (75-91) Fault Code: Left Swash Plate Sensor - Reversed
Also shown on the panel as 75-91 · Also called Drive Left Swash Plate Sensor Reversed
Left Swash Plate Sensor - Reversed · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
D7591 (panel code 75-91) sets when the drive or drive plus controller sees the left wheel or track moving the same direction as the joystick, while the left swash plate sensor reports movement in the opposite direction. The machine will keep running but drops into speed management mode until the mismatch is fixed.
High severity. The machine does not shut down, it continues to operate in speed management mode, but a reversed swash plate signal means the controller cannot trust left-side drive direction feedback. Treat it as a stop-and-diagnose issue before doing real work, since drive response may not match operator intent.
What does Bobcat error code D7591 mean?
D7591 is set by the drive or drive plus controller on Bobcat loaders and compact track/wheel loaders when it detects a contradiction between commanded direction and sensed direction on the left side drive circuit. The joystick says the left wheel or track should be moving one way, but the left swash plate position sensor is reporting the opposite.
The swash plate sensors sit at the bottom of the drive pump and are keyed to the swash plate itself, so their signal tracks the actual physical position of the plate that controls oil flow direction and volume to the drive motors. These sensors receive battery voltage from the gateway controller, and their output signal ranges from 1.0 volts to 4.0 volts depending on swash plate position.
When this code is active, the machine does not stop. It continues operating, but the drive plus controller puts it into speed management mode as a protective measure while the direction feedback conflict remains unresolved.
Common causes of D7591
- Left swash plate sensor installed incorrectly, with the sensor shaft 180 degrees out of position
- Left and right swash plate sensor connections reversed at the pump or harness
- Signal wires 3810 and 3860 reversed (or, on some harness configurations, wires 4720 and 4950 reversed)
- Fault in the drive/drive plus controller itself
- Moisture, corrosion, or pushed-back pins in the drive/drive plus controller connectors or wire harness connectors
- Intermittent fault not present at time of testing: possible causes include loose connections, corrosion, pushed-back pins, the controller, the wire harness, or a combination of these
How to troubleshoot Bobcat D7591: first checks
- Confirm the code is active: key switch on, PTOL engaged, engine running, and a forward or reverse command given, since these are the conditions under which D7591 is set
- With diagnostic software open on the swashplate feedback (FB) graphs, command drive and watch that the bars move in opposite directions on a healthy system with no swash plate codes present, then compare against the left side behavior
- Inspect the left swash plate sensor mounting at the bottom of the pump and verify the sensor shaft is correctly keyed and not installed 180 degrees rotated
- Check that left and right swash plate sensor connectors have not been swapped during a prior service or pump removal
- Trace and check continuity on signal wires 3810 and 3860 (or 4720 and 4950 depending on harness) for reversal or damage
- Inspect drive/drive plus controller connectors and wire harness connectors for moisture, corrosion, or pushed-back pins
- If the code is not currently active, treat it as intermittent and focus on connector condition, loose terminals, and harness chafe points since the root cause may not be findable in that session
How the code clears
The only clearing step listed is to cycle power. There is no separate reset procedure beyond turning the key off and back on after the underlying wiring or sensor issue has been corrected.
Affected models and serial ranges
D7591 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 fault code D7591 mean?
It means the drive or drive plus controller detected the left wheel or track moving in the same direction as the joystick command, while the left swash plate position sensor reported movement in the opposite direction. It points to a reversed or miswired sensor signal, not necessarily a broken sensor.
Can I keep driving the machine with D7591 active?
The machine will continue to operate, but it drops into speed management mode. It is not a shutdown code, but the drive direction feedback cannot be trusted, so the machine should be diagnosed before continued use, especially in tight or hazardous work areas.
What is the panel display number for D7591?
On the machine display, this code shows as 75-91.
How do I clear D7591 after fixing the problem?
Cycle the key power off and back on. No separate reset procedure is listed beyond that.
What voltage should the left swash plate sensor put out?
The sensor receives battery voltage supply from the gateway controller, and its output signal should range between 1.0 volts and 4.0 volts depending on swash plate position. A signal stuck outside that pattern or reversed relative to actual movement points to a wiring or mounting problem.
Which wires are commonly involved in a D7591 fault?
Depending on the harness configuration, signal wires 3810 and 3860, or on other configurations wires 4720 and 4950, can be reversed and trigger this code.
Why would the swash plate sensor read backwards even if it is not damaged?
The sensor shaft can be installed 180 degrees out of position, or the left and right swash plate sensor connectors can be swapped during service. Either mistake makes the sensor report movement opposite to what is actually happening, which is exactly what sets D7591.