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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 149 (ENGINE CONTROL SYSTEM - 3.8L - DTC P0220 To DTC P0449) >> DTC P0418 (L26, Nu3) >> Test Description

Test Description

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 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. 7:  This step verifies that the PCM is providing ground to the AIR pump relay when the command is ON.
  2. 8:  This step tests if a ground is constantly being applied to the AIR pump relay control circuit.
  3. 9:  This step tests for a short to voltage on the AIR pump relay control circuit. This will allow the AIR pump to run continually with the key in the OFF position. If the pump runs continually, the pump will fail.
  4. 10:  This step tests for a short to ground on the AIR pump relay control circuit. This will allow the AIR pump to operate continually with the key in the ON position. If the pump runs continually, the pump will fail.
DTC P0418 (L26, NU3)

Step Action Values Yes No
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls Component 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. Remove the underhood fuse block cover.
  3. Probe the fuse for the AIR relays with a test lamp that is connected to a good ground. Refer to Troubleshooting with a Test Lamp .
Does the test lamp illuminate on both sides of the fuse?		 - Go to Step 3  Go to Step 6 
3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 1 minute.
  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 4  Go to Testing for Intermittent Conditions and Poor Connections
4
  1. Turn OFF the ignition.
  2. Remove the secondary air injection (AIR) pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the AIR pump relay ignition 1 voltage circuit with a test lamp that is connected to good ground. Refer to Probing Electrical Connectors .
Does the test lamp illuminate?		 - Go to Step 5  Go to Step 13 
5 Measure the resistance of the AIR pump relay coil that was removed in the previous step.
Is the resistance within the specified range?		 50-70 Ω Go to Step 7  Go to Step 14 
6
IMPORTANT: The ignition 1 voltage circuit of the AIR pump relay is spliced to other components of the vehicle.
  1. Test all circuits and components that are supplied by the fuse for the AIR relays for excessive current draw. Refer to Circuit Testing and Wiring Repairs .
  2. Replace the fuse for the AIR relays, as necessary.
Did you find and correct the condition?		 - Go to Step 17  Go to Testing for Intermittent Conditions and Poor Connections
7 
  1. Connect a test lamp between the relay control circuit and the ignition 1 voltage circuit at the AIR pump relay connector.
  2. Command the AIR pump relay ON and OFF with a scan tool.
Does the test lamp turn ON and OFF with each command?		 - Go to Step 11  Go to Step 8 
8  Did the test lamp remain illuminated with each command? - Go to Step 10  Go to Step 9 
9  Test the AIR pump relay control circuit for an open or a short to voltage. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 16  Go to Step 12 
10  Test the AIR pump relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 16  Go to Step 12 
11 Test for shorted terminals and for poor connections at the AIR pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 16  Go to Step 14 
12 Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 16  Go to Step 15 
13 Repair the open or high resistance in the AIR pump relay ignition 1 voltage circuit. Refer to Wiring Repairs .
Did you complete the repair?		 - Go to Step 17  -
14 Replace the AIR pump relay. Refer to Relay Replacement (Within an Electrical Center) or Relay Replacement (Attached to Wire Harness) .
Did you complete the replacement?		 - Go to Step 16  -
15 Replace the PCM. Refer to Control Module References for replacement, setup and programming.
Did you complete the replacement?		 - Go to Step 16  -
16
  1. Ensure that all connectors and components are installed and secured.
  2. Command the AIR pump relay ON with a scan tool.
Does the AIR pump turn ON when commanded with a scan tool?		 - Go to Step 17  Go to DTC P0411 (L26, NU3) 
17
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 1 minute.
  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 18 
18 Observe the Capture Info with a scan tool.
Are there any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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