Bobcat A8503 (85-03) Fault Code: ACD/RACD Output "F" Error Off
Also shown on the panel as 85-03 · Also called ACD Output ‘F’ Error Off
ACD/RACD Output "F" Error Off · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
A8503 (panel code 85-03) sets when the Bobcat ACD/RACD controller sends voltage to energize an attachment solenoid coil on output "F", wire 5350, but detects no voltage return. The controller shuts off the output if it senses a large current draw, and the ACD/RACD icon blinks on the right instrument panel.
Medium severity. The affected attachment output on "F" will stop working, which limits attachment function, but it does not by itself indicate a loss of machine drive, braking, or lifting control. Diagnose it before relying on that attachment circuit again.
What does Bobcat error code A8503 mean?
A8503 is set by the ACD/RACD controller, which manages the Attachment Control Device / Remote Attachment Control Device system used to run hydraulically powered attachments on Bobcat loaders and compact track loaders. The controller sends a voltage out on output "F" (wire 5350) to energize an attachment solenoid coil. It then checks for voltage feedback to confirm the circuit closed correctly.
When the controller detects no voltage on that output after commanding it, or when it senses a large current draw on the circuit, it shuts the output off to protect the wiring and controller. The result is that the attachment connected to output "F" stops responding, and the ACD/RACD icon on the right instrument panel starts blinking to alert the operator.
This is an electrical fault in the attachment control circuit, not a hydraulic pump or valve failure by itself, though the end effect is a non-functioning attachment function.
Common causes of A8503
- Shorted solenoid coil on the attachment connected to output "F".
- Circuit output "F" wire 5350 to the attachment solenoid shorted to ground.
- Fault in the ACD/RACD controller itself.
- Moisture, corrosion, or pushed-back pins in the mainframe or attachment control harness connectors.
- Intermittent causes that may not be found at the time of testing, including loose connections, corrosion, pushed-back pins, the controller, the wire harness, or a combination of these problems.
How to troubleshoot Bobcat A8503: first checks
- Turn the key switch to run/enter on and watch for the ACD/RACD icon blinking on the right instrument panel to confirm the code is currently active.
- Inspect the attachment solenoid coil for a short: check coil resistance and look for obvious damage or burnt insulation.
- Trace wire 5350 from the ACD/RACD controller output "F" to the attachment solenoid connector, checking for chafing, pinched wire, or a short to ground anywhere along the run.
- Disconnect and inspect the mainframe and attachment control harness connectors for moisture, corrosion, or pins that have pushed back out of their sockets.
- If the code is not active during testing, treat it as intermittent and recheck all connections, terminals, and harness routing since the cause may not show up on a single test.
- If the wiring, connectors, and solenoid all check good, suspect the ACD/RACD controller itself.
How the code clears
Cycle power to the machine (key switch off, then back to run/enter on) once the repair is complete. No separate clearing step is listed beyond cycling power.
Affected models and serial ranges
A8503 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 ATZC11001-99999 |
| 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 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 |
Frequently asked questions
What does A8503 mean on a Bobcat machine?
It means the ACD/RACD controller sent voltage out on output "F" (wire 5350) to energize an attachment solenoid coil but did not see the expected voltage come back, or it detected a large current draw and shut the output off. The attachment on that output stops working and the ACD/RACD icon blinks on the right instrument panel.
Which Bobcat models can show code A8503?
It applies to S510, S530, S550, S570, S590, S630, S650, S750, S770, T550, T590, T630, T650, T750, and T770, and T870 models equipped with the ACD/RACD attachment control system.
Can a bad connector cause A8503 instead of a wiring short?
Yes. Moisture, corrosion, or pushed-back pins in the mainframe or attachment control harness connectors are listed causes, and they can produce the same no-feedback condition as a shorted wire or solenoid.
Why does my attachment stop working but the code clears after I cycle the key?
The controller shuts off output "F" when it senses no return voltage or a large current draw, and cycling power resets that output. If the underlying short, corrosion, or connector issue is still present, the code and the attachment shutdown will likely come back.
What if A8503 is intermittent and I can't find the cause during testing?
That is a recognized possibility with this code. If the fault isn't active when you test, probable causes still include loose connections, corrosion, pushed-back pins, the controller, the wire harness, or some combination of these. Recheck all the attachment harness connectors and terminals carefully even if nothing shows up on the first pass.
Is A8503 a hydraulic problem or an electrical problem?
It is an electrical fault in the attachment control circuit. The ACD/RACD controller and wire 5350 are what the code points to, not the hydraulic pump or valve body, even though the symptom is an attachment that won't operate.
How do I clear code A8503 after repair?
Cycle power to the machine, turning the key off and then back to run/enter on. No other clearing procedure is specified for this code.