Cause
Incorrect sensor fitted for engine
A sensor of the wrong specification fitted — physically compatible, electrically similar, calibrated differently. It plugs in, it responds, and every circuit test passes, which is why this survives a full diagnostic and is found only by checking the part number.
Airflow and pressure sensors are where it bites hardest. Two sensors that look identical can be scaled for different ranges, so the module receives a plausible value that is wrong by a consistent factor across the whole range. The result is fuel trims skewed in one direction with no leak and no fault anywhere, which is a genuinely difficult fault to chase.
Aftermarket parts and salvage parts are the usual routes in, along with a supplier substituting a superseded number. Compare the reading against a known-good expectation at a known condition — an airflow reading at idle and at a fixed speed is a strong check, and a value that is proportionally wrong rather than noisy points at calibration rather than at a fault. Verify the part number against the vehicle identification number rather than against what came off.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (3)
Codes where this is a likely explanation first, rather than merely a possible one.
Information, not instruction
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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