P2456: filter differential-pressure signal jumps too rapidly

P2456 is the quick-change diagnosis for the particulate-filter differential-pressure signal. The controller compares consecutive raw samples and flags a difference above 20.00%. It is concerned with signal dynamics, rather than a constant pressure offset or absolute filter loading.

How the monitor is enabled

The source specifies 99 failures out of 200 samples on a 12.5 ms task. Calibration, run/crank and ignition conditions must permit monitoring; cranking and diagnostic reset must be absent. Electrical-range errors and communication loss for applicable digital sensors are exclusions. Reporting is Type A, one trip.

What to preserve

A graph averaged over several seconds may hide the changes that trigger this test. Capture the available raw history and operating state before treating a normal-looking average as evidence against the code. Equally, a smooth pressure increase with exhaust flow is not automatically the excessive sample-to-sample behavior described here.

Use the related fault state to distinguish a valid but erratic signal from a signal already outside its electrical range. A hard electrical fault may inhibit the quick-change assessment. Verification requires a completed dynamic check under enabled conditions. The monitor does not identify whether the ultimate cause lies in the sensor, its electrical path or pressure transmission, so the exact vehicle diagnostic procedure is needed to choose a repair.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 833.