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Home >> Cadillac >> 2004 >> CTS Base, 3.6 7 >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 12 (Engine Controls - 2.6L & 3.2L - Diagnosis (DTC P0030 - P0174)) >> Diagnostic Trouble Codes >> DTC P0138 or P0158 >> Test Description

Test Description

WARNING: This page is about a different variant/trim than selected.

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

  1. 10:  This test verifies whether or not the affected HO2S is internally shorted to voltage prior to replacing the ECM.
  2. 15:  Both components must be replaced since the shorted HO2S has damaged the ECM low reference circuit.
DTC P0138 or P0158

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Control Module (ECM) Connector End Views  or  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2
  1. Allow the engine to idle at operating temperature. Refer to Scan Tool Data List .
  2. Observe the affected HO2S 2 parameter using a scan tool.
  3. Clear the DTCs and record the Freeze Frame/Failure Records.
  4. Operate the engine at 2,000 RPM for at least 1 minute, then allow to idle.
  5. Vary the engine speed from idle to 3,000 RPM several times within 5 seconds.
Does the voltage fluctuate above and below the specified range?		 400-597 mV Go to Step 3  Go to Step 4 
3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition and wait until scan tool communication is lost.
  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 affected heated oxygen sensor (HO2S).
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the high signal circuit of the affected HO2S harness connector on the engine control module (ECM) side, to a good ground with a DMM.
Is the HO2S high signal voltage within the specified range?		 425-475 mV Go to Step 5  Go to Step 6 
5
  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the affected HO2S high signal circuit of the ECM harness, and the affected HO2S low signal circuit of the ECM harness.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the affected HO2S parameter with a scan tool.
Is the voltage less than the specified value?		 25 mV Go to Step 11  Go to Step 8 
6 Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor (HO2S) Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 17  Go to Step 7 
7 Test the HO2S high signal circuit for an open or for high resistance. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor (HO2S) Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 17  Go to Step 8 
8
IMPORTANT: The ECM has been damaged if the circuit was shorted to a voltage source.
Test the HO2S low signal circuit for a short to voltage. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor (HO2S) Wiring Repairs in Wiring Systems.Did you find and correct the condition?		 - Go to Step 16  Go to Step 9 
9 Test the affected HO2S low signal circuit for an open or high resistance. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor (HO2S) Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 17  Go to Step 10 
10  Test for continuity between the affected HO2S heater ignition 1 voltage circuit and the affected HO2S low signal circuit at the HO2S, sensor side.
Does continuity exist?		 - Go to Step 15  Go to Step 13 
11 Inspect for the following that may affect the HO2S operation:
    NOTE: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in Cautions and Notices.
  • HO2S contamination-Inspect the HO2S for contamination.
    • NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices.
  • Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring
  • The HO2S must have a clean air reference in order to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions.
  • Exhaust system leaks or restrictions
  • Evaporative Emissions (EVAP) system malfunction-Inspect the EVAP control system. Refer to Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure .
  • Incorrect fuel pressure -Refer to Fuel System Diagnosis .

Did you find and correct the condition?		 - Go to Step 17  Go to Step 12 
12 Test for an intermittent and for a poor connection at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor (HO2S) Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 17  Go to Step 14 
13 Test for an intermittent and for a poor connection at the ECM harness connectors. 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 17  Go to Step 16 
14 Replace the affected HO2S. Refer to Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 2 or Heated Oxygen Sensor (HO2S) Replacement Bank 2 Sensor 2 .
Did you complete the replacement?		 - Go to Step 17  -
15  Replace the affected HO2S. Refer to Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 2 or Heated Oxygen Sensor (HO2S) Replacement Bank 2 Sensor 2 .
Did you complete the replacement?		 - Go to Step 16  -
16 Replace the ECM. Refer to Engine Control Module (ECM) Replacement .
Did you complete the replacement?		 - Go to Step 17  -
17
  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 18 
18 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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