P0704 — Torque Converter/Brake Switch B Circuit Malfunction
Drivable short-term, but fix now to avoid damage.
What P0704 means
This code is set when the transmission control module sees a fault in the brake switch B circuit that helps manage the torque converter clutch. The brake signal tells the transmission when to release the converter lock-up, so a bad signal can cause shuddering or harsh engagement. Common fixes include replacing or adjusting the brake light switch and repairing wiring or connectors.
Common symptoms
- Check engine light is on
- Torque converter shudder or vibration
- Harsh or slipping shifts
- Cruise control won't engage
- Brake lights behave abnormally
Common causes
- Faulty or out-of-adjustment brake light switch
- Damaged or corroded wiring in the brake switch circuit
- Blown fuse related to the brake switch
- Failing transmission control module
- Loose or poor ground connection
Typical repair cost
$100 – $450
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0704 code?
Short trips are usually fine, but it's not ideal. Because the code affects torque converter lock-up, you may feel shuddering or rough shifts that can wear the transmission over time. Have it looked at soon.
How much does it cost to fix a P0704 code?
A brake switch replacement typically costs $100 to $200. If wiring repair or control module work is needed, expect $300 to $450 or more depending on the vehicle.
Is a P0704 code serious?
It's worth taking seriously. The fault can cause torque converter shudder and harsh shifting, which may lead to transmission wear if left unfixed. The root cause is often inexpensive, so prompt repair pays off.
What is the brake switch B circuit?
It's a secondary brake signal circuit the transmission uses to know when you're braking. This tells it to disengage the torque converter clutch smoothly, so a fault here disrupts converter operation.