What does the code P2431 mean?

Here is the diagnostic chart for P2431.

DTC P2431

DTC DESCRIPTOR

DTC P2431
Secondary Air Injection (AIR) System Pressure Sensor Performance

DIAGNOSTIC FAULT INFORMATION
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Diagnostic Trouble Code Tests and Associated Procedures

TYPICAL SCAN TOOL DATA

AIR Pressure Sensor

CIRCUIT/SYSTEM DESCRIPTION
The secondary air injection (AIR) system aids in the reduction of hydrocarbon emissions during a cold start. The system forces fresh filtered air into the exhaust stream in order to accelerate the catalyst operation. An electric air pump, the secondary AIR injection pump, provides filtered air on demand to the AIR control solenoid valve/pressure sensor assembly. The AIR control solenoid valve/pressure sensor assembly controls the flow of air from the AIR pump to the exhaust manifold. The AIR solenoid valve relay supplies the current needed to operate the AIR solenoid valve/pressure sensor assembly. A pressure sensor is used to monitor the air flow from the AIR pump. The control module supplies the internal pressure sensor with a 5-Volt reference, an electrical ground, and a signal circuit.

The AIR diagnostic uses 3 phases to test the AIR system:

DTCs P0411 and P2430 run during Phase 1
DTCs P2430 and P2440 run during Phase 2
DTC P2444 runs during Phase 3
In all 3 phases, testing is accomplished by comparing the measured pressure against the expected pressure. The control module can detect faults in the AIR pump, AIR solenoid valve/pressure sensor assembly, and the exhaust check valve. The pressure sensor can also detect leaks and restrictions in the secondary AIR system plumbing. Refer to Secondary Air Injection (AIR) System Description for further information.

CONDITIONS FOR RUNNING THE DTC

DTCs P0106, P0107, P0108, P0412, P0418, P0606, P0641, P0651, P2432, P2433 are not set.
The ignition is ON.
The AIR pump is commanded OFF.
DTC P2431 runs continuously when the above conditions are met.
CONDITIONS FOR SETTING THE DTC
The control module determines that the difference between the AIR pressure sensor and the barometric pressure (BARO) value is greater than 10 kPa when the AIR pump is commanded OFF.
OR
The control module determines that the difference between the AIR pressure sensor and the BARO value is greater than 50 kPa when the AIR pump is commanded ON.

ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
CIRCUIT/SYSTEM VERIFICATION

If DTCs P0641 or P0651 are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis. See: Diagnostic Trouble Code Descriptions
With the ignition ON and the engine OFF, observe that the MAP sensor parameter is correct for your altitude. Refer to Altitude vs Barometric Pressure.
If the MAP sensor parameter is not correct, refer to DTC P0106. See: P0106
With the ignition ON and the engine OFF, observe that the AIR Pressure Sensor parameter is nearly identical to the MAP sensor parameter.
With the engine running, enable the AIR pump relay with a scan tool and observe that the AIR Pressure Sensor parameter equals approximately 10-15 kPa above BARO.
With the engine running, enable the AIR System with a scan tool and observe that the AIR Pressure Sensor parameter equals approximately 8-10 kPa above BARO.
CIRCUIT/SYSTEM TESTING

With the ignition ON and the engine OFF, observe the AIR Pressure Sensor parameter with a scan tool while manipulating all related wiring and connectors.
If manipulation does affect the AIR Pressure Sensor parameter then repair the harness or connector.
With the ignition ON, the engine OFF, and the solenoid valve disconnected, measure for a voltage range of 4.8-5.2 volts between the 5-Volt reference circuit and a good ground.
If less than 4.8 volts then test the 5-Volt reference circuit for high resistance, If the circuit test normal, replace the control module.
With the ignition ON, the engine OFF, and the solenoid valve disconnected, inspect for an AIR Pressure Sensor parameter reading on a scan tool of approximately 40 kPa.
If more than approximately 40 kPa, test the signal circuit for a short to voltage, If the circuit test normal, replace the control module.
With the ignition ON, the engine OFF, the solenoid valve disconnected, and a 3-amp fused jumper installed between the signal and 5-Volt reference circuits, inspect for an AIR Pressure Sensor parameter reading on a scan tool of approximately 140 kPa
If less than approximately 140 kPa, test the signal circuit for an open, or a short to ground. If the circuit test normal, replace the control module.
With the ignition ON, the engine OFF, the solenoid valve disconnected, a 300 ohm fixed resistor, an appropriate length of secondary ignition wire may be adequate, installed between the 5-Volt reference circuit and the low reference circuit, and a fused jumper connected from the signal circuit to the 5-Volt reference circuit at the fixed resistor, observe an AIR pressure sensor parameter reading on a scan tool of 5.0 volts.
If less than 5.0 volts, test the 5-Volt reference circuit and the signal circuit for high resistance, If the circuit test normal, replace the control module.
With the ignition ON, the engine OFF, the solenoid valve disconnected, a 300 ohm fixed resistor, an appropriate length of secondary ignition wire may be adequate, installed between the 5-Volt reference circuit and the low reference circuit, and a 3-amp fused jumper connected from the signal circuit to the low reference circuit at the fixed resistor, observe for a pressure sensor parameter reading on a scan tool of 0 volts.
If more than 0 volts, test the low reference circuit for high resistance, If the circuit test normal, replace the control module.
If all circuits and the control module test normal, replace the solenoid valve.
REPAIR INSTRUCTIONS

Secondary Air Injection Check Valve Replacement
Control Module References for engine control module (ECM) replacement, setup and programming
REPAIR VERIFICATION

With the key ON and the engine OFF, observe that the AIR Pressure Sensor parameter is approximately equal to BARO.
With the engine running, enable the AIR pump relay with a scan tool and observe that the AIR Pressure Sensor parameter equals approximately 10-15 kPa above BARO.
With the engine running, enable the AIR System with a scan tool and observe that the AIR Pressure Sensor parameter equals approximately 8-10 kPa above BARO.