P0408 — Exhaust Gas Recirculation Sensor B Circuit Low
Drive with caution — fix soon.
What P0408 means
This code means the engine computer is reading too low a voltage from the 'B' EGR position sensor, which monitors how the exhaust gas recirculation valve moves. It usually points to a wiring fault, a bad sensor, or a sticking EGR valve. It's a fairly common code and is often fixable without major engine work.
Common symptoms
- Check engine light is on
- Rough idle or slight engine shaking
- Hesitation or reduced power on acceleration
- Slightly worse fuel economy
- May fail an emissions test
Common causes
- Faulty EGR position sensor (B)
- Short to ground in the sensor circuit
- Damaged or corroded wiring or connector at the EGR sensor
- Failing or stuck EGR valve
- Poor power supply or ground to the sensor
Typical repair cost
$150 – $450
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0408 code?
For short trips, usually yes, since it's mostly an emissions and sensor issue and won't normally leave you stranded. But you shouldn't rely on it long-term, because a faulty EGR system hurts fuel economy and can cause an emissions test failure. Have it diagnosed soon.
How much does it cost to fix a P0408?
Most repairs fall between about $150 and $450. Wiring or connector fixes are cheaper, while replacing the EGR position sensor or the EGR valve raises the cost.
Is a P0408 code serious?
It's not an emergency and rarely strands you, but it shouldn't be ignored. Over time it can worsen fuel economy, cause rough running, and lead to a failed emissions test.
What does the 'B' sensor circuit low mean in P0408?
It means the EGR position sensor 'B' is sending a voltage lower than expected, typically caused by a short to ground, a failing sensor, or a damaged connector rather than serious engine damage.