P0407: EGR Sensor B Circuit Low Voltage
The P0407 code indicates that the Engine Control Module (ECM) has detected a low voltage signal from the Exhaust Gas Recirculation (EGR) sensor B circuit. This sensor monitors the position of the EGR valve or the flow of exhaust gases. A low voltage reading suggests a short to ground, faulty sensor, or wiring issue. The EGR system reduces NOx emissions by recirculating exhaust gases back into the intake, and a malfunction can affect engine performance and emissions.
01. Most Common Causes
- Faulty EGR sensor B
- Short to ground in EGR sensor B circuit
- Open or damaged wiring/connectors
- Corroded or loose electrical connections
- Failed ECM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or engine hesitation
- Increased emissions
- Failed emissions test
- Possible decrease in fuel economy
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the EGR sensor B wiring and connector for damage, corrosion, or loose connections.
Step 3: Test the EGR sensor B voltage with a multimeter; compare to manufacturer specifications.
Step 4: Check for continuity and shorts in the circuit between the sensor and ECM.
Step 5: If wiring is good, replace the EGR sensor B and clear the code.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause rough idling, reduced performance, and increased emissions. Prolonged driving could damage the EGR system or catalytic converter.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on the vehicle and whether the sensor or wiring needs replacement.