C0123 is a chassis/ABS diagnostic trouble code associated with a fault in an ABS hydraulic solenoid valve circuit on applicable vehicles. The exact definition of C0123 can vary depending on the vehicle manufacturer, ABS system, and model year.
On some ABS systems, including applicable Subaru applications, C0123 refers to a front outlet solenoid valve on the right-hand side. The manufacturer-specific service information should always be checked before diagnosis or repair.
Fault Code Description
C0123 can indicate a malfunction involving the front right ABS outlet solenoid valve.
The ABS outlet solenoid valve is part of the hydraulic control system that regulates brake-fluid pressure during ABS operation. The ABS control module monitors the electrical operation of the solenoid and may store C0123 when the detected condition is outside the expected range.
C0123 does not automatically mean that the complete ABS hydraulic unit has failed. Wiring, connectors, electrical resistance, power supply, or an internal ABS hydraulic-control fault can also cause the code.
What Does C0123 Mean?
C0123 means that the ABS system has detected a fault associated with an ABS outlet solenoid valve circuit.
On systems that use the right-front valve definition, the affected component is the front right outlet solenoid valve. The exact component location and code definition depend on the vehicle.
C0123 ABS System Operation
During ABS operation, the control module uses hydraulic solenoid valves to increase, hold, or reduce brake pressure at individual wheels. The outlet valve helps release or regulate hydraulic pressure when the ABS system needs to prevent wheel lockup.
Symptoms of C0123
- 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 may be stored.
- ABS braking performance may be affected during emergency braking.
The exact symptoms depend on the vehicle and the ABS control strategy.
Common Causes of C0123
- Faulty front right ABS outlet solenoid valve.
- Open solenoid valve circuit.
- Shorted solenoid circuit.
- Damaged ABS wiring.
- Corroded electrical connector.
- Loose or damaged terminals.
- Incorrect solenoid resistance.
- Poor ABS module power supply.
- Poor electrical ground.
- Internal hydraulic control unit fault.
- ABS control module fault.
- Water or contamination in the connector.
How to Diagnose C0123
1. Scan the ABS Module
Use an ABS-capable scan tool to confirm C0123 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.
2. Check ABS Power and Ground
Verify that the ABS control module receives the correct power supply and has a reliable ground connection. Low voltage or poor grounding can cause incorrect 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 front right outlet 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 outlet 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 external wiring, connector, power, ground, and solenoid circuits have been tested.
C0123 Diagnostic Signal Flow
Is C0123 Serious?
C0123 should be treated as an important ABS fault.
A malfunctioning ABS outlet solenoid can affect the system's ability to control hydraulic 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 C0123?
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 it has been inspected.
C0123 Repair Cost
The repair cost for C0123 depends on the actual cause of the ABS fault. Electrical repairs are generally less expensive than replacing the 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 C0123. 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 C0123 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
C0123 may appear together with other ABS codes. Related faults should be considered before replacing components.
Related ABS Codes
- C0120 – ABS valve/solenoid circuit fault on applicable systems.
- C0121 – ABS valve/solenoid circuit 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 valve/solenoid circuit fault on applicable systems.
- C0126 – ABS valve/solenoid circuit fault on applicable systems.
FAQ About C0123
What does C0123 mean?
C0123 is an ABS/chassis diagnostic trouble code. On applicable systems, it indicates a fault involving an ABS outlet solenoid valve, including the front right outlet valve on some vehicles.
What causes C0123?
Possible causes include a faulty solenoid valve, open or shorted wiring, poor electrical connections, damaged terminals, poor ABS power or ground, or an internal hydraulic-control-unit fault.
Is C0123 an ABS code?
Yes. C0123 is a chassis-related code associated with the ABS system on applicable vehicles.
Can a bad ABS solenoid cause C0123?
Yes. A defective outlet solenoid can cause C0123 on systems using this definition. However, the solenoid circuit and connector should also be tested before replacing the component.
Can I drive with C0123?
Driving should be minimized until the ABS system is diagnosed because ABS and related electronic braking functions may be unavailable.
Does C0123 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 C0123?
Start by scanning the ABS module, checking ABS power and ground, inspecting the hydraulic-unit connector, and testing the applicable outlet solenoid circuit according to the manufacturer's specifications.
Final Result
C0123 is an ABS/chassis diagnostic trouble code associated with an ABS outlet solenoid valve fault on applicable vehicles. On some systems, the affected component is the front right outlet 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 C0123 is manufacturer-dependent, always verify the exact definition, component location, connector pinout, electrical specifications, and diagnostic procedure for the specific vehicle.