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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 70 (Engine Control System - 3.8L (DTC P1125 To DTC P2A01)) >> Diagnosis >> DTC P2431 (L26, Nu3) >> Test Description

Test Description

WARNING: This page is about a different car, the 2005 Buick LaCrosse and 2005 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 3:  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.
  2. 4:  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.
  3. 7:  This step inspects for excessive resistance in the reference voltage circuit. If the test lamp does not illuminate at all, there is resistance in the circuit.
  4. 9:  This step tests for high electrical resistance in the AIR pressure sensor circuit.
  5. 10:  This step tests for high electrical resistance in the AIR pressure sensor low reference circuit.
DTC P2431 (L26, NU3)

Step Action Values Yes No
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2
  1. Turn ON the ignition, with the engine OFF.
  2. Monitor the MAP sensor and AIR pressure sensor parameters with the scan tool.
Is the difference between the values more than the specified value?		 8 kPa Go to Manifold Absolute Pressure (MAP) Sensor Diagnosis Go to Step 3 
3 
  1. Start the engine.
  2. Monitor the DTC information with the scan tool.
Is DTC P0641 also set?		 - Go to DTC P0641 Go to Step 4 
4 
  1. Turn ON the ignition, with the engine OFF.
  2. Listen for secondary air injection (AIR) pump operation.
Is the AIR pump ON?		 - Go to DTC P2444 (L26, NU3)  Go to Step 5 
5
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the AIR pressure sensor voltage parameter with a scan tool.
Is the pressure sensor voltage within the specified value?		 2.5-2.7 V Go to Step 6  Go to Step 7 
6
  1. Start and idle the engine.
    2. IMPORTANT: The AIR diagnostic may command either or both the AIR pump relay and AIR valve relay ON when the engine is started. Allow the engine to operate approximately 2 minutes before commanding the AIR relays with the scan tool.
  2. Monitor the AIR Pressure Sensor parameter.
    3. IMPORTANT: When the AIR pump relay is commanded ON with the scan tool, only the AIR pump relay is energized. When the AIR valve relay is commanded ON with the scan tool, both the AIR pump and the AIR valve relays are energized.
  3. Command the AIR pump relay ON with the scan tool.
  4. Command the AIR valve relay ON with the scan tool.
  5. Subtract the maximum value measured with the AIR valve relay ON from the maximum value with the AIR pump relay ON.
Is the difference at least the specified amount?		 0.2 V Go to Diagnostic Aids Go to Step 7 
7 
  1. Turn OFF the ignition.
  2. Disconnect the AIR control solenoid valve/pressure sensor assembly electrical connector.
  3. Connect a test lamp to the 5-volt reference circuit of the harness and to a good ground.
  4. Turn ON the ignition, with the engine OFF.
Does the test lamp illuminate at least dimly?		 - Go to Step 8  Go to Step 12 
8 Measure the voltage between the AIR pressure sensor signal and the 5-volt reference circuits at the connector harness using a DMM.
Is the voltage near the specified value?		 4.9 V Go to Step 10  Go to Step 9 
9 
  1. Test the AIR pressure sensor circuit for high resistance. Refer to Testing for Intermittent Conditions and Poor Connections .
  2. Repair as necessary. Refer to Wiring Repairs .
Was a repair necessary?		 - Go to Step 12  Go to Step 11 
10 
  1. Test for high resistance in the low reference circuit of the AIR pressure sensor between the sensor and the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections .
  2. Test for a poor electrical connection at the pressure sensor.
  3. Repair as necessary. Refer to Wiring Repairs .
Did you find and correct a condition?		 - Go to Step 14  Go to Step 11 
11 Replace the AIR pressure sensor. Refer to Secondary Air Injection (AIR) Shut-Off Valve Replacement .
Did you complete the replacement?		 - Go to Step 14  -
12 Repair the high resistance in the 5-volt reference circuit of the AIR pressure sensor circuit. Refer to Testing for Intermittent Conditions and Poor Connections .
Did you complete the repair?		 - Go to Step 14  -
13 Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 14  -
14
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start and idle the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 15 
15 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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