Cause
Blocked or kinked sensor line
The small line connecting a pressure sensor to the point it measures, blocked or kinked so the reading no longer follows what is happening. The sensor is faultless and honest about the pressure at its own port — which is now isolated from the system.
A blocked line gives a flat, plausible trace, which is the dangerous outcome: nothing looks broken, the value sits in range, and the module acts on a number that stopped changing. A reading that barely moves between idle and load is the tell, and it is only visible if you look at how the value behaves rather than what it is.
Exhaust pressure lines soot up and evaporative lines crush. The first is a steel tube into the exhaust that fills with carbon; the second is plastic under the vehicle that a jack or a kerb flattens. Clear and inspect the line whenever a pressure sensor is suspected — it costs nothing, and a new sensor into a blocked line reproduces the fault exactly.
Typically a moderate job.
Codes this can cause (3)
Codes where this is a likely explanation first, rather than merely a possible one.
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