Exhaust Gas Recirculation Sensor A Circuit High
The EGR sensor is sending a voltage signal that's too high, like a thermostat reading the room as hotter than it actually is. The engine computer thinks exhaust gases aren't flowing properly through the recirculation system.
The ECM monitors the EGR sensor's voltage output to verify exhaust gas recirculation flow. When voltage remains above the acceptable threshold, the ECU detects a circuit high condition. This typically indicates a stuck sensor, wiring short, or faulty EGR valve.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| EGR Sensor Voltage | 0.5–4.5 volts (varies by manufacturer) | Above 4.7 volts or stuck at max voltage |
| EGR Flow Detection | Sensor responds to valve open/close cycles | No voltage change when EGR valve operates |
Code P0407 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, P0407 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.