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Home >> Chevrolet >> 2005 >> Classic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System (DTC P0106-P0300) >> Diagnosis >> DTC P0138 >> Test Description
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Test Description

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

  1. 2:  When the system is operating correctly, the HO2S 2 voltage should toggle above and below the bias voltage.
  2. 5:  This step tests the HO2S 2 high signal circuit for a short to voltage.
DTC P0138

Step Action Values Yes No
Schematic Reference: Engine Controls Schematics
Connect 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 in Vehicle DTC Information
2 
  1. Operate the engine at normal operating temperature.
  2. Operate the engine above 1,200 RPM for 2 minutes.
  3. Observe the HO2S 2 voltage parameter with the scan tool.
Does the scan tool indicate that the heated oxygen sensor (HO2S) 2 voltage is more than the specified value?		 1,042 mV Go to Step 4  Go to Step 3 
3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start 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 Intermittent Conditions
4
  1. Turn OFF the ignition.
  2. Disconnect the HO2S 2 sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the HO2S 2 high signal circuit on the powertrain control module (PCM) side of the harness connector to a good ground with the DMM.
Does the voltage measure within the specified range?		 350-550 mV Go to Step 6  Go to Step 5 
5  Test the HO2S 2 high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 11  Go to Step 8 
6 The HO2S 2 is detecting a rich exhaust condition or may be contaminated. Inspect for one of the following conditions:
Repair any of the above or similar engine conditions as necessary.
Did you find and correct the condition?		 - Go to Step 11  Go to Step 7 
7 Inspect for poor connections at the harness connector of the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 11  Go to Step 9 
8 Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 11  Go to Step 10 
9
IMPORTANT: Before replacing a contaminated HO2S, determine and repair the cause of the contamination.
Replace the HO2S 2. Refer to Heated Oxygen Sensor (HO2S) Replacement (Bank 1) or Heated Oxygen Sensor (HO2S) Replacement (Bank 2) .Did you complete the replacement?		 - Go to Step 11  -
10 Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 11  -
11
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start 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 12 
12 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 in Vehicle DTC Information System OK
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