P0408: EGR Sensor B Circuit High Voltage
The P0408 code indicates that the Engine Control Module (ECM) has detected a high 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 high voltage reading typically means the sensor is reporting a value outside the expected range, often due to a short to voltage, a faulty sensor, or wiring issues. This can lead to improper EGR operation, affecting engine performance and emissions.
01. Most Common Causes
- Faulty EGR sensor B
- Short to voltage in the EGR sensor B circuit
- Damaged wiring or connector
- Corroded terminals
- Faulty ECM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or stalling
- Poor engine performance
- Increased emissions
- Failed emissions test
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 shorts to voltage or ground in the circuit.
Step 5: If wiring is intact, 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?▼
It is generally not recommended to drive with this code as it can cause poor engine performance and increased emissions. However, if the vehicle is running fine, you may drive short distances to a repair shop.
How much does it cost to fix?▼
The cost to fix P0408 typically ranges from $50 to $150 for parts and labor, depending on the cause and vehicle make/model.