P2431

DTC P2431 (WITH RPO CODE NU3)

SYSTEM DESCRIPTION
The DTC P2431 secondary air injection (AIR) system pressure sensor performance diagnostic monitors the accuracy of the sensor signal. The 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 AIR 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 valve relay supplies the current needed to operate the AIR control solenoid valve/pressure sensor assembly. A pressure sensor is used to monitor the air flow from the AIR pump. The powertrain control module (PCM) supplies the internal pressure sensor with a 5-volt reference, an electrical ground, and a signal circuit. By comparing the measured pressure against the expected pressure, the PCM can detect faults in the AIR pressure sensors, the AIR pump, the AIR control/shut-off valve, and the exhaust check valve. The pressure sensor can also detect leaks in the AIR system plumbing.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P2431 Secondary Air Injection (AIR) System Pressure Sensor Performance

CONDITIONS FOR RUNNING THE DTC
- DTCs P0107, P0108, P0412, P0418, P0606, P0641, P0651, P2432, P2433 are not set.
- The ignition is ON.
- DTC P2431 runs continuously when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
The PCM determines the difference between the AIR pressure sensor and the barometric pressure (BARO) sensor signals is greater than 10 kPa when the AIR pump is commanded OFF.

OR

The PCM determines the difference between the AIR pressure sensor and the BARO sensor signals 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.

DIAGNOSTIC AIDS
- This DTC may set due to an incorrect manifold absolute pressure (MAP)/ BARO value caused by a faulty MAP sensor. Before replacing any component ensure that this condition does not exist.
- The barometric (BARO) pressure value is initially based on the MAP sensor value at key ON. The BARO value is used to calculate the predicted AIR pressure sensor value.
- An intermittent malfunction may be caused by a fault in an AIR pressure sensor electrical circuits. Inspect the wiring harness and components for an intermittent condition.
- If the DTC cannot be duplicated, the information included in the Freeze Frame can be useful in determining vehicle operating conditions when the DTC was first set.

TEST DESCRIPTION

Step 1 - Step 7:

Step 8 - Step 16:

Step 17 - Step 25:

The numbers below refer to the step numbers on the diagnostic table.
5. If the AIR pump is always ON, DTC P2431 can set. DTC P2444 will locate and repair the cause of an AIR pump stuck in the ON position.
6. This step determines if DTC P2431 is the result of a hard failure or an intermittent condition. Normal pressure sensor input voltage is approximately 2.6 volts with the ignition ON, the engine OFF, and the AIR pump OFF.
13. This step places a known load in the circuit in order to verify proper voltage drop. An appropriate length of secondary ignition wire may be adequate for a fixed 300 ohm resistor.
15. The low reference, the AIR pressure signal, the 5-volt reference circuits and the PCM have tested OK. Replace the AIR control solenoid valve/pressure sensor assembly.