P0341 and P0344: camshaft sensor range and intermittent signal
An intermittent camshaft signal is one of the harder faults to pin down, because the car works perfectly most of the time. Here is how to catch it.
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P0351 to P0358: ignition coil primary and secondary circuit by cylinder
These codes name the cylinder, which is more than a misfire code does at first. But the code names a circuit, and the circuit includes more than the coil.
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P0365 to P0369: camshaft position sensor B circuit
Sensor B is usually the exhaust camshaft. On a twin-cam engine with variable timing on both shafts, that sensor is doing real work — not sitting there as a spare.
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P0400 and P0403: EGR flow malfunction and control circuit
P0400 says the exhaust gas is not flowing. P0403 says the valve is not being commanded properly. One is usually carbon; the other is usually electrical.
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P0404: EGR position sensor range/performance explained
P0404 compares commanded EGR position against measured position. Carbon, not electronics, is behind most of them — and cleaning beats replacing far more often than parts sellers admit.
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P0405 and P0406: EGR position sensor A low and high
These are the feedback side of the EGR system. Without a trustworthy position signal the ECU is commanding a valve blind, and it will not do that for long.
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P0411 to P0414: secondary air injection flow and valve circuit
The system only runs for a minute after a cold start, which is why the fault is nearly invisible and the code arrives with no symptom at all.
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P0421 and P0422: warm-up catalyst efficiency below threshold
A separate code for the close-coupled catalyst, and a separate meaning: this one is usually about how the engine behaves in the first minute, not about the converter.
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P0440 and P0446: EVAP purge and vent valve faults
These two codes point at the valves that seal and breathe the fuel vapour system. A stuck purge valve is one of the few EVAP faults you can actually feel while driving.
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P0441: EVAP incorrect purge flow — the valve that never opens
Not a leak code. This one says the purge valve is not moving the vapour it should, which is a different repair from every other EVAP code.
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P0442: small EVAP leak — finding a hole you cannot see
P0442 means a leak around 1 mm across somewhere in the fuel vapour system. Guessing costs more than testing, and the fuel cap is innocent more often than the internet claims.
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P0443 to P0445: EVAP purge valve control circuit
Electrical codes for a valve that is easy to reach and easy to test. This is one of the more DIY-friendly items on the EVAP system.
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