OBD Code P0407: Exhaust Gas Recirculation Sensor A Circuit High

Q: What does OBD code P0407 mean?

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.

Q: What are the symptoms of fault code P0407?

Check Engine Light illuminated, Rough idle or engine hesitation during acceleration, Increased emissions or failed emissions test

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What This Actually Means

In plain language — no jargon

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.

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Symptoms You May Notice

3 known symptoms for this code

Check Engine Light illuminated

Rough idle or engine hesitation during acceleration

Increased emissions or failed emissions test

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Embedded Systems Insight

What the ECU/ECM is actually computing

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.

Voltage & Parameter Thresholds

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

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

EGR sensor wiring harness

Inspect connector for corrosion, loose pins, or bent terminals and clean or reseat the connection.

2

EGR sensor

Replace the sensor if voltage remains high after harness inspection and cleaning.

3

EGR valve

Clean or replace if valve is stuck open, preventing proper sensor signal variation.