Bobcat H4603 (46-03) Fault Code: Left Blinker Error Off
Also shown on the panel as 46-03
Left Blinker Error Off · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
H4603 (panel code 46-03) sets when the Bobcat auxiliary controller commands the left blinker relay but does not detect voltage back on signal wire 6420. It points to a wiring, relay, or controller problem in the left turn signal circuit, not a dash light malfunction by itself.
Low severity. This code affects the left turn signal only. It does not disable drive, lift, or hydraulic functions, but a non-working blinker is a real road-safety and compliance issue if the machine travels on public roads or shared jobsite paths. Fix it before operating where signaling matters.
What does Bobcat error code H4603 mean?
H4603 is set by the auxiliary controller when it sends a command to activate the left blinker relay but does not see the expected voltage return on signal wire 6420. The left blinker switch, mounted on the left grip, is what initiates this command when the operator activates it.
In plain terms, the controller is telling the switch to turn on the left blinker relay and then checking for confirmation that it happened. If that confirmation voltage is missing, the code sets. This is a feedback-circuit fault, not necessarily a failure of the bulb or light itself.
Affected models include the S510, S530, S550, S570, S590, S630, S650, S750, S770 skid steers and T550, T590, T630, T650, T750, T770, T870 compact track loaders.
Common causes of H4603
- Signal wire 6420 shorted to ground
- Left blinker relay failure
- Auxiliary controller fault
- Moisture, corrosion, or pushed-back pins in the auxiliary controller connectors, AWS horn/blinker harness, or the mainframe harness
- Loose connections, corrosion, pushed-back pins, controller issues, or wire harness problems in combination, particularly if the code is intermittent and not present at the time of testing
How to troubleshoot Bobcat H4603: first checks
- Turn the key switch to run/enter on and try activating the left blinker switch on the left grip to confirm the fault is repeatable
- Inspect the auxiliary controller connectors, the AWS horn/blinker harness, and the mainframe harness for moisture, corrosion, or pushed-back pins
- Trace signal wire 6420 for signs of chafing, pinching, or a short to ground, especially where it passes through frame junctions or connectors
- Check the left blinker relay for proper operation and secure seating in its socket
- Wiggle-test connectors and harness sections near the auxiliary controller while watching for the blinker to intermittently work, since intermittent faults may not be present at the time of testing
How the code clears
Once the repair is complete, cycle power (turn the key switch off, then back to run/enter on) to clear the code. No separate clearing step is listed beyond a power cycle.
Affected models and serial ranges
H4603 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, SN A3PH11001-99999 |
Frequently asked questions
What does Bobcat code H4603 mean?
It means the auxiliary controller commanded the left blinker relay on but did not detect the expected voltage on signal wire 6420, indicating a problem somewhere in that left turn signal circuit.
Will H4603 stop my Bobcat from driving or lifting?
No. This code is limited to the left blinker circuit. It does not affect drive, lift, or hydraulic functions, but it should be fixed promptly for safe road or jobsite operation.
Where is the left blinker switch located?
The left blinker switch is located on the left grip of the machine.
Why does my H4603 code come and go?
Intermittent H4603 codes are usually caused by loose connections, corrosion, or pushed-back pins in the harness or connectors, which can create a temporary open or short that clears itself when the connection shifts. If the code isn't active during testing, the exact cause may not be identifiable at that time.
How do I clear the H4603 code after repair?
Cycle power by turning the key switch off and back to run/enter on. No additional clearing procedure is listed.
What is signal wire 6420 on a Bobcat?
Wire 6420 carries the signal between the auxiliary controller and the left blinker relay. A short to ground on this wire is one of the listed causes of H4603.
Which Bobcat models can show code H4603?
H4603 applies to the S510, S530, S550, S570, S590, S630, S650, S750, S770 skid steer loaders and the T550, T590, T630, T650, T750, T770, T870 compact track loaders.