What is the difference between P0407 and P0408?

P0407 means sensor B signal is too low (short to ground or failed sensor). P0408 means sensor B signal is too high (open wire, missing ground, or sensor failed open). The diagnostic approach is similar, but the failure modes are opposite.

Can I drive with P0408?

Short distances yes. The ECU may stop using the affected EGR circuit, and some diesels enter limp mode. Long-term driving accelerates intake carbon buildup and may trigger secondary DPF or SCR faults. Plan repair within a few weeks.

Which engines have an EGR sensor B?

Only engines with two EGR valves or two EGR circuits. Many modern diesels combine a high-pressure and a low-pressure EGR circuit, each with its own valve and position feedback (many VW Group EA288 engines work this way), and the manufacturer decides which one is called B. On an engine with a single EGR valve, P0408 is unusual: recheck the code and look up the manufacturer's own definition.

Do I have to replace both EGR valves?

Not always, but it is worth considering on a high-mileage engine with two EGR valves, because both share the same age, soot exposure and thermal cycling. If one has failed, the other may not be far behind, and the labour for the second can be lower if the work overlaps.

P0408: Exhaust Gas Recirculation Sensor "B" Circuit High

Quick Answer

Safe to drive (short-term)

P0408 means EGR position sensor 'B' is sending a voltage above its normal operating range. Sensor B only exists on engines with a second EGR valve or a second EGR circuit, such as diesels that combine high-pressure and low-pressure EGR. The fault is usually an open signal wire, a missing ground, or a sensor that has failed internally.

Severity: Moderate · Emissions
Estimated repair cost: From €70 to €730+, varies by vehicle

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What does P0408 mean?

P0408 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0408 and illuminates the check engine light.

Where it is on the car

Engine
Exhaust manifold
EGR cooler (diesels and many newer petrols)
EGR valve and position sensor
Intake manifold

Sensor B exists only on engines with a second EGR valve or a second EGR circuit, for example some diesels with high and low pressure EGR.

What are the symptoms of P0408?

If your vehicle has triggered P0408, you may notice one or more of these symptoms:

Check engine light illuminated
Rough or uneven idle
Reduced power and possible limp mode on diesels
Hesitation during light throttle
Failed emissions or periodic technical inspection

What causes P0408?

Here are the most common causes of P0408:

Sensor B failed internally, driving its signal high
: high
Open signal wire or broken connector pin on sensor B
: high
Missing sensor B ground connection
: medium
Loose or unseated sensor B connector after recent service
: medium
Failed ECU 5V reference circuit (rare, usually affects multiple sensors)
: low

Is it safe to drive with P0408?

Generally yes, for short-term driving. Driveable. P0408 affects the second EGR position sensor (sensor B), reporting a voltage above the expected range. The ECU may stop using the affected EGR circuit, and some diesels reduce power. Expect rough idle, reduced power and a likely rejection at an emissions check.

How do you diagnose P0408?

Follow these steps to pinpoint the root cause of P0408:

Identify which physical valve or sensor is 'B' in the manufacturer's service data. On engines with high- and low-pressure EGR it belongs to one of the two circuits, and manufacturer-level software names it directly
Back-probe sensor B signal wire. Reading near 5V with key on indicates an open signal or sensor failed open
Verify sensor B ground at the connector. Missing ground will let the signal float high
Inspect for loose connector locks, especially after recent intake or turbo service
If signal stays high with the connector fully seated and ground confirmed, replace the integrated valve or sensor assembly, then have the EGR adaptation carried out with manufacturer-level software

How much does P0408 cost to fix?

Repair costs for P0408 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Re-seat and clean sensor B connector	€10–€60	€60–€180	€70–€240	Moderate
Replace EGR valve B (sensor integrated)	€150–€450	€100–€280	€250–€730	Moderate
Repair EGR sensor B wiring harness branch	€20–€120	€120–€350	€140–€470	Professional

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

EGR Valve Replacement Cost

P0408 on specific vehicles

P0408 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0408 on Volkswagen

Volkswagen Golf

See Volkswagen-specific causes & cost

These codes are often seen alongside P0408 or indicate related issues:

Common questions about P0408

What is the difference between P0407 and P0408?: P0407 means sensor B signal is too low (short to ground or failed sensor). P0408 means sensor B signal is too high (open wire, missing ground, or sensor failed open). The diagnostic approach is similar, but the failure modes are opposite.
Can I drive with P0408?: Short distances yes. The ECU may stop using the affected EGR circuit, and some diesels enter limp mode. Long-term driving accelerates intake carbon buildup and may trigger secondary DPF or SCR faults. Plan repair within a few weeks.
Which engines have an EGR sensor B?: Only engines with two EGR valves or two EGR circuits. Many modern diesels combine a high-pressure and a low-pressure EGR circuit, each with its own valve and position feedback (many VW Group EA288 engines work this way), and the manufacturer decides which one is called B. On an engine with a single EGR valve, P0408 is unusual: recheck the code and look up the manufacturer's own definition.
Do I have to replace both EGR valves?: Not always, but it is worth considering on a high-mileage engine with two EGR valves, because both share the same age, soot exposure and thermal cycling. If one has failed, the other may not be far behind, and the labour for the second can be lower if the work overlaps.

Read our detailed guides

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