P0407: EGR Sensor B Circuit Low
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 typically means the sensor signal is below the expected range, which can be caused by a faulty sensor, wiring issues, or a malfunctioning EGR valve. This can lead to improper EGR flow, affecting engine performance and emissions.
1. Most Common Causes
- Faulty EGR sensor B
- Open or shorted wiring in sensor circuit
- Corroded or loose electrical connector
- Failed EGR valve (stuck open or closed)
- Carbon buildup on EGR valve or passages
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or engine hesitation
- Increased emissions
- Poor fuel economy
- Engine stalling
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect EGR sensor B connector and wiring for damage or corrosion.
Step 3: Test sensor voltage and ground with a multimeter; compare to manufacturer specs.
Step 4: Check EGR valve operation by applying vacuum or using a scan tool to command it open/closed.
Step 5: Clean EGR passages and valve if carbon buildup is present.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe for short distances, but prolonged driving may cause poor performance, increased emissions, and potential damage to the EGR system or catalytic converter.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether the sensor or valve needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.