Torque Converter/Brake Switch B Circuit Low
Your transmission's brake switch signal is too weak or missing, like a dimly lit brake light that the computer can't properly detect. This prevents the torque converter from operating correctly and may cause transmission shifting problems.
The ECM monitors the brake switch input voltage to detect when brakes are applied, which signals when to release the torque converter lock. A low voltage reading below the expected threshold triggers this fault. The ECU expects a clean 5V signal when brakes are released and near 0V when applied.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Brake Switch Voltage | 4.5V–5.0V (released) / 0V–0.5V (applied) | Below 1.5V continuously or erratic transitions |
| Signal Resistance | Less than 10 ohms when closed | Greater than 50 ohms indicating poor contact |
Code P0720 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0720 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.