What it means
This code has no standardized generic meaning in the SAE/ISO list. Its meaning, if used by your vehicle, depends on the manufacturer.
How it works
C0594 is not a standardized OBD-II code, so its title alone cannot confirm that the fault concerns brake booster motor A. If a vehicle uses this code, the relevant component and the condition that sets it are defined by that manufacturer.
Common causes
Most likely first.
- Manufacturer-specific code definition
- Vehicle-specific diagnostic data needed
Symptoms
- Symptoms depend on the vehicle-specific fault
How to diagnose it
- Check the vehicle’s service information to confirm whether C0594 is supported and what system it identifies.
- Scan all modules with a tool that can read manufacturer-specific chassis codes, and record the reporting module and any related codes.
- Review the freeze-frame or fault record and vehicle-specific data available for the reporting module.
- Inspect the identified component, its connectors, and nearby wiring for damage, looseness, or corrosion.
- Follow the manufacturer’s diagnostic procedure to test the named circuit or component before replacing parts.
Common fixes
- Repair damaged or loose wiring or connector terminals identified during inspection.
- Restore any poor power or ground connection identified by the vehicle-specific tests.
- Complete the manufacturer-specified repair for the confirmed component or circuit fault.
- Replace or reprogram a module only if the vehicle-specific diagnosis confirms it is faulty or incorrectly configured.
Can I keep driving?
Driving advice cannot be determined from C0594 alone because its meaning varies by manufacturer. If a brake warning appears or braking feels different, stop somewhere safe and have the vehicle checked before driving further.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.