C0124 is a specific chassis/ABS diagnostic trouble code associated with a fault in an ABS hydraulic solenoid valve circuit on applicable vehicles. The exact definition can vary between manufacturers, ABS systems, and model years.
On some ABS systems, including applicable Subaru applications, C0124 refers to a rear inlet solenoid valve on the left-hand side. Always verify the exact definition using vehicle-specific service information before diagnosis or repair.
Fault Code Description
C0124 can indicate a malfunction involving an ABS hydraulic solenoid valve. On systems using the rear-left valve definition, the affected component is the rear left inlet solenoid valve.
The ABS control module uses hydraulic solenoid valves to regulate brake-fluid pressure at individual wheels during ABS operation. If the electrical or functional condition of the monitored valve is outside the expected range, the ABS module may store C0124.
C0124 does not automatically mean that the complete ABS hydraulic unit has failed. Wiring, connectors, solenoid resistance, power supply, grounding, or an internal hydraulic-control-unit fault can also cause the code.
What Does C0124 Mean?
C0124 means that the ABS system has detected a malfunction associated with an ABS hydraulic solenoid valve.
On systems that use the rear-left valve definition, C0124 identifies the rear left inlet solenoid valve. The exact component and description are manufacturer-dependent.
C0124 ABS System Operation
During ABS operation, the control module commands hydraulic solenoid valves to control brake-fluid pressure. The inlet valve controls the flow of hydraulic pressure into the corresponding brake circuit.
Symptoms of C0124
- ABS warning light.
- Traction control warning light.
- Electronic stability control warning light.
- Brake system warning message.
- ABS function may be disabled.
- Traction control may be disabled.
- Stability control may be disabled.
- Additional ABS fault codes.
- ABS pressure control may not operate correctly.
The exact symptoms depend on the vehicle and its ABS control strategy.
Common Causes of C0124
- Faulty ABS inlet solenoid valve.
- Open solenoid circuit.
- Shorted solenoid circuit.
- Damaged ABS wiring.
- Corroded electrical connector.
- Loose or damaged connector terminals.
- Incorrect solenoid resistance.
- Poor ABS module power supply.
- Poor electrical ground.
- Water or contamination in the connector.
- Internal ABS hydraulic control unit fault.
- ABS control module fault.
How to Diagnose C0124
1. Scan the ABS Module
Use an ABS-capable scan tool to confirm C0124 and check for additional ABS, wheel-speed sensor, hydraulic, traction-control, or communication codes.
Record the stored codes and available freeze-frame information before clearing the fault memory.
2. Check ABS Power and Ground
Verify the ABS control module has the correct power supply and a reliable ground connection. Low voltage or poor grounding can create solenoid-related faults.
3. Inspect the ABS Connector
Inspect the ABS hydraulic-control-unit connector for corrosion, water intrusion, damaged terminals, loose connections, or overheating.
4. Check the Solenoid Wiring
Use the vehicle-specific wiring diagram to identify the applicable ABS solenoid circuit.
Check for an open circuit, short circuit, excessive resistance, damaged insulation, or poor terminal contact.
5. Check Solenoid Resistance
Measure the resistance of the applicable solenoid according to the manufacturer's specifications.
Do not use a universal resistance value because ABS solenoid specifications vary between vehicles.
6. Check the Hydraulic Unit
If the wiring and electrical connections are correct but the solenoid does not meet the manufacturer's test requirements, the ABS hydraulic control unit may require further diagnosis.
7. Check the ABS Module
An internal ABS control-module or hydraulic-unit fault should only be considered after the wiring, connector, power, ground, and solenoid circuits have been tested.
C0124 Diagnostic Signal Flow
Is C0124 Serious?
C0124 should be treated as an important ABS fault.
A malfunctioning ABS hydraulic solenoid can affect the system's ability to control brake pressure correctly during ABS operation.
Depending on the vehicle, ABS, traction control, electronic stability control, or other electronic braking functions may be disabled.
Can I Drive With C0124?
Driving should be minimized until the ABS fault has been diagnosed.
The conventional hydraulic brakes may continue to operate on some vehicles, but ABS and related electronic safety functions may not operate correctly.
If braking performance is reduced, the brake pedal feels abnormal, or a red brake warning light is illuminated, the vehicle should not be driven until the braking system has been inspected.
C0124 Repair Cost
The repair cost for C0124 depends on the actual cause of the ABS fault. Wiring and connector repairs are generally less expensive than replacing an ABS hydraulic control unit or ABS module.
- ABS diagnostic testing: approximately $80–$180.
- Wiring or connector repair: approximately $80–$350.
- ABS solenoid repair: approximately $200–$600+ where separately serviceable.
- ABS hydraulic control unit: approximately $500–$1,500+.
- ABS control module: approximately $400–$1,500+.
- Complete ABS hydraulic assembly: approximately $600–$2,000+ on some vehicles.
These are general estimates only. Actual costs vary according to the vehicle, model year, parts prices, labor rates, and the component that has failed.
Important: Do not replace the ABS module or hydraulic unit based only on C0124. Proper electrical and ABS testing should be completed first.
Common Repair Mistakes
Replacing the ABS Module Immediately
Do not replace the ABS module simply because C0124 is stored. Check the wiring, connector, power supply, ground, and solenoid circuit first.
Replacing the Hydraulic Unit Without Testing
A damaged connector or open circuit can produce symptoms similar to an internal hydraulic-unit failure.
Using the Wrong Solenoid Specification
ABS solenoid resistance and control strategies vary between systems. Always use the correct manufacturer specification.
Ignoring Other ABS Codes
C0124 may appear together with other ABS codes. Related faults should be considered before replacing components.
Related ABS Codes
- C0120 – ABS solenoid/valve fault on applicable systems.
- C0121 – ABS solenoid/valve fault on applicable systems.
- C0122 – Front right inlet solenoid valve malfunction on applicable systems.
- C0123 – Front right outlet solenoid valve malfunction on applicable systems.
- C0124 – ABS solenoid valve malfunction on applicable systems.
- C0126 – ABS solenoid valve malfunction on applicable systems.
FAQ About C0124
What does C0124 mean?
C0124 is an ABS/chassis diagnostic trouble code associated with an ABS hydraulic solenoid valve fault on applicable vehicles. The exact definition depends on the manufacturer and ABS system.
What causes C0124?
Possible causes include a faulty ABS solenoid, open or shorted wiring, poor electrical connections, damaged terminals, poor ABS power or ground, or an internal hydraulic-control-unit fault.
Is C0124 an ABS code?
Yes. C0124 is a chassis-related diagnostic code associated with the ABS system on applicable vehicles.
Can a bad ABS solenoid cause C0124?
Yes. A defective hydraulic solenoid can cause C0124 on systems using this definition. However, the solenoid circuit and connector should also be tested before replacing the component.
Can I drive with C0124?
Driving should be minimized until the ABS system is diagnosed because ABS and related electronic braking functions may be unavailable.
Does C0124 mean the ABS module is bad?
Not necessarily. Wiring, connectors, power, grounds, and the solenoid valve should be tested before condemning the ABS control module.
What should I check first for C0124?
Start by scanning the ABS module, checking ABS power and ground, inspecting the hydraulic-unit connector, and testing the applicable solenoid circuit according to the manufacturer's specifications.
Final Result
C0124 is an ABS/chassis diagnostic trouble code associated with an ABS hydraulic solenoid valve fault on applicable vehicles. On some systems, the affected component is the rear left inlet solenoid valve.
The most reliable diagnosis is to inspect the ABS power supply, grounds, connector, wiring, and solenoid circuit before replacing the hydraulic unit or ABS control module.
Because C0124 is manufacturer-dependent, always verify the exact definition, component location, connector pinout, electrical specifications, and diagnostic procedure for the specific vehicle.