Idle Switch (Electric Control Throttle) Circuit Malfunction
Your vehicle's electronic throttle system isn't properly detecting when the engine is at idle, similar to a car that can't tell the difference between stopped and moving. The ECU is having trouble communicating with the idle position sensor on the throttle body.
The ECM monitors the electronic throttle position sensor to detect when the throttle is fully closed (idle position). It compares the signal voltage against expected thresholds and looks for continuity in the idle switch circuit. A break in the circuit or out-of-range voltage triggers this fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Idle Switch Voltage | 0.5–4.5V when throttle closed | Out of range or no signal detected |
| Circuit Resistance | Below 10 ohms (continuous path) | Open circuit or resistance above 100 ohms |
Code P1516 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, P1516 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.