Electronic Feedback Signal Not Detected
The engine control computer isn't receiving a response signal from a feedback sensor or actuator, like a sensor that's supposed to confirm a component is working. It's like pressing a doorbell but never hearing it ring back to confirm someone got the message.
The ECU sends commands to various actuators and expects to receive confirmation feedback signals within a specified timeframe. When the feedback signal fails to return or is too weak to detect, the ECU logs a fault. This typically applies to oxygen sensors, mass airflow sensors, or solenoid feedback circuits.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Feedback Signal Voltage | 0.4-4.6V within expected response time | No signal or signal outside valid range for >2 seconds |
| Sensor Response Time | Signal detected within 500ms of command | No response or delayed response >1 second |
Code P1684 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, P1684 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.