Diagnostic engine · built by DMS Tuned

Your fault code is a starting point.
Not a diagnosis.

Search the code. Understand what the ECU actually measured. Follow the order to check things in — not a list of parts to replace blindly. Every page says what the code does not prove.

In depth: P0011 · P0087 · P00AF · P0101 · P0106 · P0171 · P0172 · P0234 · P0243 · P0299 · P0300 · P0301 · P0401 · P0420 · P2263 · P2563 · or look up any of 12,000+ codes →

Fault codes 16 codes in the boost / air / fuelling cluster, each with the real diagnostic order. Browse codes → Boost log analyser Drop in a requested-vs-actual boost log. Runs in your browser — the file never leaves your machine. It tells you what the log can and cannot prove. Open the analyser → Engine hubs 8 platforms with their ECUs and common codes, branched by boost-control architecture. Browse engines →

See it work · 15 seconds

Your ECU asked for boost. Did it get it?

The boost log analyser compares what the ECU requested against what the engine delivered, finds the full-load region on its own, and names the shape of the gap. Below is what a persistent undertrack looks like — actual boost rises with the request but plateaus short and never closes the gap.

Illustrative Requested vs actual boost · not a measurement from any vehicle
0.0 0.4 0.8 1.2 1.6 0s1s2s3s4s5s bar Requested Actual

Example shape: actual builds but plateaus around 0.9 bar and never reaches the 1.40 bar request — the gap is the fault.

Run this example in the analyser → Read your own log →

The example runs entirely in your browser. On your own log the analyser prints the exact figures — and refuses to judge when the data can't support it.

Why this is not another code dictionary

The order is the product. A list of "possible causes" is what every parts site publishes, and it is why people replace parts blindly. We tell you what to check first, and why.
Architecture-aware. A wastegated petrol engine and a variable-geometry diesel fail in a different order. A check that belongs to one is noise on the other — our pages branch for it.
Evidence, not confidence. Every fact carries where it came from. We can confirm an underboost in a log; we will not claim the wastegate is the cause before the test that proves it.
Honest about sign-off. The diagnostic order is technically reviewed. Where no tuner has yet put their name to it, the page says so out loud.

Behind What the Fault

A real ECU-tuning shop, not a content farm.

WhatTheFault is built and reviewed by DMS Tuned — years of ECU calibration, diagnostics and forced-induction work. If your code needs a human, you can message the engineers directly. When you need a workshop near you instead, we point you to VROUM, not to ourselves.

Ask the engineers