Diagnostic engine · 16 codes covered deeply

Fault codes

We cover a focused cluster — boost control, air measurement and fuelling — in the depth that actually changes what you do next. Each page gives the order to check things in, not a parts list.

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Valve timing

P0011 Camshaft Position — Timing Over-Advanced (Bank 1) The variable valve timing on bank 1 is further advanced than the ECU commanded, or will not return. VVT runs on oil pressure, so this is an oil story far more often than a hardware one.

Fuelling

P0087 Fuel Rail / System Pressure Too Low Actual fuel pressure fell below what the ECU commanded. On a modern direct-injection engine this is a request-vs-actual pressure problem, and where it falls away decides everything. P0171 System Too Lean (Bank 1) The fuelling control system has hit its lean-correction limit on bank 1 — it has been adding fuel to compensate for something and has run out of adjustment. It is a mixture-control threshold, not a reading from any one sensor. P0172 System Too Rich (Bank 1) The fuelling control has hit its rich-correction limit on bank 1 — it has been pulling fuel out to compensate for something and has run out of adjustment. It is a mixture threshold, not a reading from one sensor.

Boost control

P00AF Turbocharger / Supercharger Boost Control "A" Module Performance Something in the boost-control chain is not performing the way the ECU expects. Manufacturers word this code quite differently, so what "module" means here depends on the engine. P0234 Turbocharger / Supercharger Overboost The engine produced more boost than the ECU allowed, so it cut back to protect itself. P0243 Wastegate Solenoid A Malfunction The electrical circuit controlling the wastegate solenoid is not behaving as expected. P0299 Turbocharger / Supercharger Underboost Your ECU asked for boost. The engine did not deliver enough of it, for long enough that the ECU logged a fault. P2263 Turbocharger / Supercharger Boost System Performance The boost system is not performing the way the ECU expects. This one is deliberately broad: depending on the manufacturer it can be logged for too little boost OR too much, so the direction has to be established before anything else. P2563 Turbocharger Boost Control Position Sensor Range / Performance The feedback that tells the ECU where the boost-control actuator actually is does not agree with where it was told to go. On most engines that carry this code it is a variable-geometry actuator.

Air measurement

P0101 Mass Air Flow Circuit Range / Performance The airflow the MAF reports does not agree with what the ECU expects from the throttle, boost and rpm it can see. P0106 MAP / Barometric Pressure Circuit Range / Performance The manifold pressure reading is not plausible for the conditions the ECU can otherwise measure.

Misfire

P0300 Random / Multiple Cylinder Misfire The ECU detected misfires but could not attribute them to one cylinder. "Random" means unattributed, not that every cylinder is failing. P0301 Cylinder 1 Misfire The ECU attributed misfires specifically to cylinder 1. Because it names a cylinder, one swap test splits ignition from everything mechanical.

Emissions

P0401 Exhaust Gas Recirculation Flow Insufficient The ECU commanded EGR flow and did not see enough of it. This is about flow, not the electrical circuit, and the usual culprit is carbon, not electronics. P0420 Catalyst System Efficiency Below Threshold (Bank 1) The ECU judged the catalytic converter to be storing less oxygen than it expects, by comparing the sensors before and after it. That judgement can be fooled.