What does it mean?
In this case the humidity signal usually stays inside its normal voltage window, but it jumps, cuts out or changes far faster than the moisture content of the air actually can. Alongside the fixed range tests the module runs continuity and rate of change checks, and it stores this code when the input behaves unstably rather than settling on a wrong value. Faults of this type are almost always mechanical connection problems: a terminal that loses contact when the engine rocks, or insulation rubbed thin against a bracket. Because the failure comes and goes, the lamp may appear and clear over several drive cycles before the code becomes permanent.
Symptoms
- MIL that switches on and off over several journeys
- Brief hesitation or a soft spot in acceleration that cannot be reproduced on demand
- Humidity value visibly jumping on a scan tool while conditions are steady
- Occasional knock on gasoline engines or a puff of smoke on diesels
- Idle that is inconsistent from one start to the next
- Fuel consumption that drifts up without a clear reason
Likely causes
- Loose or spread terminals in the sensor or module connector
- Chafed harness making momentary contact with ground or another circuit under vibration
- Moisture inside the connector producing a resistance that changes with temperature
- Cracked sensing element that opens intermittently as it heats
- High resistance ground splice that only shows up under load
- Harness pulled tight over a mounting point so movement stresses the conductor
- Contamination on the element causing unstable, jumpy readings
How to fix it
- Start from the freeze frame and note whether the fault appears on rough roads, in the wet or when the engine is hot
- Graph the humidity signal live and perform a wiggle test on the connector and harness with the engine running
- Use a scope where possible, since short drop-outs can be too fast for a scan tool to display
- Measure voltage drop on the sensor ground and reference circuits while flexing the harness
- Open the connector, inspect for moisture and corrosion, and check that each terminal grips its mating pin firmly
- Repair damaged insulation, re-pin poor terminals and re-route harness sections that rub or stretch
- Replace the sensor last, only after the wiring is proven and the instability follows the sensor itself