A faulty front right outlet solenoid valve inside the ABS hydraulic modulator assembly.; Damaged, corroded, or open wiring in the circuit between the ABS module and the front right outlet valve solenoid.; A poor electrical connection at the ABS module connector or at the valve body harness, often due to water intrusion or terminal fretting.; An internal failure in the ABS control module's driver circuit for that specific valve.; Low brake fluid level or air trapped in the front right hydraulic circuit, causing the valve performance test to fail.; A restricted or collapsed brake hose at the front right wheel that alters pressure release characteristics.; A weak or failing ABS pump motor that cannot build or release pressure quickly enough during the valve test.

DTC codes / C03xx · Brakes, steering and suspension / C0304

C0304Outlet Valve Front Right Performance

Q: What does code C0304 mean?

Outlet Valve Front Right Performance. C0304 indicates that the antilock braking system (ABS) control module has detected a performance fault with the front right outlet valve, which is the solenoid valve that releases hydraulic pressure from that wheel's brake circuit during antilock operation. The module monitors valve response and circuit integrity, and it sets this code when the valve does not react as expected during a self-test or active ABS event.

C0304 indicates that the antilock braking system (ABS) control module has detected a performance fault with the front right outlet valve, which is the solenoid valve that releases hydraulic pressure from that wheel's brake circuit during antilock operation. The module monitors valve response and circuit integrity, and it sets this code when the valve does not react as expected during a self-test or active ABS event.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaBrakes, steering and suspension

Symptoms you may notice

The ABS warning light stays illuminated on the dashboard.
The traction control or stability control warning light may also come on because those systems share the same hydraulic modulator.
The ABS may be disabled, leaving only conventional braking with a risk of wheel lockup during hard stops.
A soft, spongy, or unusually firm brake pedal feel may develop if the valve is stuck partially open or closed.
During low-speed braking or a panic stop, the driver may feel a pulsation or hear a cycling noise from the hydraulic modulator that does not match normal ABS operation.
Often no symptoms besides the warning light, especially if the fault is intermittent or only detected during the module's self-test.

Common causes, most likely first

A faulty front right outlet solenoid valve inside the ABS hydraulic modulator assembly.
Damaged, corroded, or open wiring in the circuit between the ABS module and the front right outlet valve solenoid.
A poor electrical connection at the ABS module connector or at the valve body harness, often due to water intrusion or terminal fretting.
An internal failure in the ABS control module's driver circuit for that specific valve.
Low brake fluid level or air trapped in the front right hydraulic circuit, causing the valve performance test to fail.
A restricted or collapsed brake hose at the front right wheel that alters pressure release characteristics.
A weak or failing ABS pump motor that cannot build or release pressure quickly enough during the valve test.

How to diagnose and fix it

Verify the code with a scan tool that can read ABS module data and check for any related pending or history codes before replacing parts.
Inspect the brake fluid level and condition, then check for leaks or air in the front right brake circuit and bleed the system if needed.
Visually inspect the wiring harness and connector at the ABS module and at the front right wheel for corrosion, chafing, or loose terminals.
Perform a resistance and continuity test on the front right outlet valve solenoid circuit using the manufacturer's wiring diagram and specified values.
Command the outlet valve on and off with a bidirectional scan tool while listening for a distinct click and monitoring hydraulic pressure response.
If the valve does not respond electrically or hydraulically, replace the ABS hydraulic modulator assembly or the affected valve body component as required.
After repair, clear the codes, perform the ABS module calibration or self-test, and take the vehicle on a safe road test to confirm the code does not return.

Why the outlet valve code misleads

A low brake fluid level or air in the front right circuit can set C0304 even when the outlet valve itself is mechanically sound, because the module's performance test relies on expected pressure changes.
Corroded terminals at the ABS module connector are a frequent cause that is overlooked when technicians jump straight to replacing the expensive hydraulic modulator.
The outlet valve is only active during antilock braking events, so a vehicle can pass a basic brake inspection and still have a valve that fails the module's automated self-test.
A failing ABS pump motor or a weak accumulator can produce valve performance codes because the valve cannot release pressure if the pump cannot supply it correctly.
This code does not always mean the ABS modulator is defective; wiring faults, fluid issues, and even a collapsed brake hose can mimic the same symptom.

Can I keep driving with C0304?

You can usually drive the vehicle with the ABS warning light on, but the antilock braking system will be disabled, so maintain extra following distance and avoid hard braking or slippery conditions. Have the fault diagnosed promptly, because a valve that sticks open or closed can affect brake balance and increase stopping distances in an emergency.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.