The mirror image of P0401 – this code indicates the EGR system is flowing too much exhaust gas into the intake. Often a stuck-open valve or a faulty differential pressure sensor, not a catastrophic failure. Here's what to check and in what order.
P0402 means the ECU is detecting more EGR flow than commanded – the opposite of P0401. On most BMW diesels this is caused by a stuck‑open EGR valve or a faulty differential pressure sensor. It rarely indicates internal engine damage, and the fix is usually straightforward.
Do not assume the valve needs replacing – a simple clean or sensor test may solve it. Full diagnostic order below.
In a modern BMW common-rail diesel, the EGR system is carefully controlled by the ECU. The differential pressure sensor across the EGR cooler and the temperature sensor measure the actual flow. When the measured flow exceeds the commanded flow by a significant margin – typically more than 30% – the ECU logs P0402. This is the exact opposite of P0401 (insufficient flow). The most common cause is a valve that fails to close fully due to carbon fouling, or a sensor that reports incorrectly. Unlike P0401, a stuck-open EGR valve can cause rough idling, increased fuel consumption, and even engine stalling at low speeds. The code appears across all BMW diesel families – from N47 and B47 four‑cylinder units to N57 and B57 six‑cylinder engines – and the diagnostic approach is largely the same.
Ordered by how often each turns out to be the real culprit – with typical fitted cost against each, so you can sanity‑check any quote you've been given.
| Cause | Likelihood | Typical Cost (fitted) | Notes |
|---|---|---|---|
| EGR valve stuck open (carbon fouling) | Very High | £180–£380 | Cleaning often restores function; replacement if the shaft is seized |
| Faulty differential pressure sensor | High | £250–£450 | Reports incorrect flow; can be tested with live data |
| Wiring or connector issues (sensor signal) | Medium | £100–£250 | Corrosion or loose pins at sensor plugs |
| EGR cooler internal leak (passing) | Low | £600–£1,000 | Rare; usually accompanied by coolant loss |
| ECU software / calibration error | Very Low | £100–£300 | Can occur after ECU updates or tuning; dealer reflash may fix |
Cost figures [PATTERN DATA] – indicative independent BMW specialist pricing, not drawn from our engine replacement dataset.
Compare commanded EGR position vs actual flow. If flow is high even at idle, suspect a stuck-open valve.
Check sensor output with a vacuum pump or substitute a known‑good unit. Many P0402 cases are misdiagnosed as valve faults when the sensor is the issue.
Remove and inspect. If it doesn't close fully, clean it or replace if the shaft is worn.
Inspect sensor plugs for corrosion; perform continuity tests from sensor to ECU.
If all else is clear, check for software updates or tuning-related changes.
Our diagnostic wizard walks the same order, or confirm your engine with the registration lookup.
Yes, but with caution. P0402 itself is not immediately engine‑destroying, but a stuck‑open EGR valve can cause rough running, stalling at low speeds, and increased fuel consumption. If the engine stalls repeatedly or the car enters limp mode, avoid motorway driving. The primary risk is that excessive EGR flow can lead to carbon buildup in the intake manifold over time, which may eventually cause performance issues. Get it diagnosed within a few days; a simple clean or sensor swap usually resolves it. If you notice significant power loss or stalling, stop driving and arrange recovery.
Yes, for short trips to a garage. Avoid motorways if the engine stalls or limp mode is active. Prolonged driving with a stuck-open valve can lead to carbon buildup and reduced performance.
No. Often a clean is sufficient, and in many cases the differential pressure sensor is the real culprit – cheaper and easier to replace than the valve itself.
Only temporarily. The code will return as soon as the ECU sees the flow discrepancy again, typically within one drive cycle. Clearing it also erases freeze‑frame data that helps with diagnosis.
Expect 1–2 hours of diagnostic time at an independent BMW specialist, typically £100–£200. Many specialists will waive or offset this if you proceed with the repair.
Some BMW models had EGR cooler recalls (e.g., certain N47 and B47 engines). Check your VIN against BMW UK recalls or use our recall checker.
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