Output Circuit Check Signal High
The ECU detects that a control output signal is stuck at a higher voltage than expected, like a light switch that won't turn fully off. This typically indicates a wiring or component problem preventing the output from reaching its proper low state.
The ECU monitors the voltage level of an output control circuit to verify it's functioning correctly. When the ECU commands the circuit low, it should drop to near ground voltage; a high voltage reading indicates the circuit isn't responding to commands. This is typically measured through feedback or diagnostic circuits that monitor solenoid drivers, relay outputs, or similar actuators.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Output Control Voltage | 0.5V or less when commanded low | Greater than 2.0V when commanded low |
| Circuit Resistance | Less than 5 ohms | Open circuit or excessive resistance |
Code P1668 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, P1668 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.