Diagnostic article Generic OBD-II
P2431: secondary-air pressure is compared before engine cranking
The GM P2431 example compares AIR pressure with manifold and boost-pressure references at rest, after excluding their circuit faults.
Read before applying this article
Documented application
GM 2009 09OBDG06 Engine Diagnostics, cited pre-cranking secondary-air pressure rationality monitor only. Document-level evidence does not establish per-code vehicle, engine or wiring applicability.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P2431 is a secondary-air pressure rationality check in this GM 2009 example. The table compares AIR pressure with manifold and turbocharger boost-pressure references before engine cranking. It is not an evaluation of normal running pressure differences under boost.
A stationary comparison uses several references
The source requires zero vehicle speed and zero engine speed with ignition on. It excludes the specified AIR, boost-pressure and manifold-pressure circuit faults. The comparison uses a short sequence of three readings at a 25-millisecond cycle time.
The printed logic contains several pressure-difference combinations. These distinguish AIR-to-reference disagreement from circumstances in which the other reference measurements also disagree. A single AIR pressure value therefore does not contain all the information needed to interpret the result.
Identify which comparison failed
A technician should preserve the three pressure reports and their circuit-fault states from the same stationary event. Replacing one of those readings with a value captured after cranking would change the operating condition and could invalidate the comparison.
The monitor does not automatically identify the AIR sensor as the faulty component, nor does it prove a blocked secondary-air passage. It supplies a rationality finding that needs the matching vehicle diagnostic procedure. The table provides no universal sensor-location mapping or connector test. Verification should establish a qualified, internally consistent pressure comparison rather than relying only on a cleared code or a plausible isolated sensor reading.
Source and applicability
GM 2009 09OBDG06 Engine Diagnostics, cited pre-cranking secondary-air pressure rationality monitor only. Document-level evidence does not establish per-code vehicle, engine or wiring applicability.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
AIR System Air Flow/Pressure Sensor Circuit Range/Performance Bank 1
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT