Failed 2-4 brake timing solenoid valve itself, often due to internal coil failure or contamination; Damaged or corroded wiring harness connector at the transmission solenoid pack; Open or shorted wire in the circuit between the TCM and the solenoid valve; Contaminated transmission fluid (ATF) causing solenoid sticking or poor electrical contact; Faulty TCM, though this is less common and should be diagnosed last; Internal transmission mechanical wear causing the solenoid to work outside its expected electrical parameters; Loose or damaged ground connection for the transmission control system

DTC codes / Subaru codes / P1704

P1704 · Subaru2-4 Brake Timing Solenoid Valve Circuit Malfunction

Q: What does code P1704 mean?

2-4 Brake Timing Solenoid Valve Circuit Malfunction. P1704 on a Subaru means the transmission control module (TCM) has detected an electrical fault in the circuit for the 2-4 brake timing solenoid valve, which is a critical shift-control solenoid inside the automatic transmission valve body. The computer monitors the solenoid's commanded current versus the actual current flow and sets this code when the circuit is open, shorted, or out of expected resistance range.

P1704 on a Subaru means the transmission control module (TCM) has detected an electrical fault in the circuit for the 2-4 brake timing solenoid valve, which is a critical shift-control solenoid inside the automatic transmission valve body. The computer monitors the solenoid's commanded current versus the actual current flow and sets this code when the circuit is open, shorted, or out of expected resistance range.

SystemPowertrain

Code typeSubaru specific

SeverityMedium

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms
Harsh or delayed shifts, especially when engaging the 2-4 brake band during upshifts or downshifts
Transmission may enter limp mode, holding a single gear or refusing to shift
Flashing 'AT OIL TEMP' light or 'Sport' mode indicator on the dash
Poor fuel economy or unusual engine RPM fluctuations during steady-speed driving
In some cases, the vehicle may start off in a higher gear or feel sluggish from a stop

Common causes, most likely first

Failed 2-4 brake timing solenoid valve itself, often due to internal coil failure or contamination
Damaged or corroded wiring harness connector at the transmission solenoid pack
Open or shorted wire in the circuit between the TCM and the solenoid valve
Contaminated transmission fluid (ATF) causing solenoid sticking or poor electrical contact
Faulty TCM, though this is less common and should be diagnosed last
Internal transmission mechanical wear causing the solenoid to work outside its expected electrical parameters
Loose or damaged ground connection for the transmission control system

How to diagnose and fix it

Verify the code with a scan tool that can read Subaru-specific transmission codes and check for any related codes in the TCM
Inspect the transmission fluid level and condition; a low or burnt fluid level can cause solenoid performance issues
Disconnect the battery and inspect the solenoid valve connector and wiring for corrosion, chafing, or loose pins
Measure the resistance of the 2-4 brake timing solenoid with a multimeter and compare to Subaru specifications
Check for continuity and short-to-ground on the wires between the TCM and the solenoid connector
If the solenoid fails electrical tests, replace the solenoid valve, which may require removing the transmission pan or valve body
After repair, clear the code and perform a relearn or adaptation drive cycle as specified for the Subaru transmission

What Subaru techs check before replacing the solenoid

A common misdiagnosis is replacing the solenoid when the real problem is a chafed wire in the harness near the transmission mount, so always perform a wiggle test on the harness while monitoring solenoid resistance.
Contaminated transmission fluid from neglected service intervals can cause the solenoid to stick mechanically and set P1704 even when the electrical circuit tests good, so fluid condition is a critical first check.
The 2-4 brake timing solenoid is part of the valve body assembly on many Subaru transmissions, and replacing just the solenoid requires careful cleaning of the valve body passages to prevent debris from damaging the new part.
P1704 can be set intermittently by a poor ground connection at the transmission case, so checking and cleaning ground points is a cheap step that often resolves the issue.
On some Subaru models, a failing TCM can mimic a solenoid circuit fault, but TCM failure is rare and should only be considered after all wiring and solenoid tests pass.

Can I keep driving with P1704?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because the transmission may shift harshly or enter limp mode. If the transmission is stuck in a single gear or the warning light is flashing, stop driving and have the vehicle towed to prevent further damage.

Tools that help

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