Subsidiary Throttle Valve Solenoid Circuit Malfunction
The ECU detected an electrical problem with the secondary throttle valve solenoid—the valve that helps control airflow isn't responding correctly. Think of it like a stuck relay switch that controls a gate; the gate won't open or close when commanded.
The ECU commands the subsidiary throttle solenoid and monitors the circuit voltage and current draw to confirm activation. It detects opens, shorts, or excessive resistance in the solenoid winding or its control circuit. If voltage or current falls outside expected parameters, the fault is logged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid Control Voltage | 12V nominal when commanded ON | <10V or >14.5V, or no response |
| Circuit Current Draw | 0.5–2.0 A when energized | <0.1 A (open) or >3.0 A (short) |
Code P1533 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, P1533 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.