P0495: Fan speed high is judged against an estimated limit

P0495 is a cooling-fan speed-performance code. In this GM implementation the controller subtracts a maximum estimated fan speed from actual fan 1 speed. The relevant evidence is that difference, not simply a loud fan or a single high rpm reading.

A mapped deviation persists over time

The table gives a calibration-dependent difference threshold of 1,300–4,050 rpm and points to lookup table 34. Those values are not a universal normal fan-speed range. They belong to a comparison against the controller’s estimate.

The condition is evaluated over 20 seconds and uses two-trip reporting. Supply and commanded-fan conditions also qualify the monitor. A short speed spike or a reading without the expected-speed context cannot independently reproduce this test.

Compare command, estimate and actual speed

A useful scan record retains the commanded fan percentage and the actual speed, together with the applicable estimated limit or manufacturer diagnostic context. A fan commanded to run rapidly is not automatically exhibiting the deviation described by P0495.

The source does not establish a failed fan motor, controller or wiring path from the code alone. It supplies monitor logic rather than a hands-on fan test. Keep clear of powered cooling fans and use the correct service procedure to investigate speed feedback and control behavior. Monitor completion under the required conditions is more informative than merely clearing the stored warning.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 815.