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HOMESERVICE MANUALSCHEVROLET2006COBALT SS, 4D SEDAN, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 299 (ENGINE CONTROL SYSTEM - 3.6L (LY7) - DTC P0008 TO DTC P0133)DTC P0123TEST DESCRIPTION
2006 Chevrolet Cobalt SS, 4D Sedan, Standard

Test Description

2006 Chevrolet Cobalt SS, 4D Sedan, StandardSECTION 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. 2:  This step verifies that a condition exists.
  2. 5:  This step tests the signal circuit for a short to voltage. If the scan tool displays a voltage after the TP sensor is disconnected, the circuit is shorted to a voltage.
  3. 7:  This step tests for high resistance in the low reference circuit of the TP sensor. The ECM must be completely powered down to obtain an accurate resistance reading. It may take up to 30 minutes for the ECM to power down after the ignition key is removed. Removal of the ECM fuse or the PCM/ETC fuse, allows the ECM to power down completely.
  4. 8:  This step tests the low reference circuit for a short to voltage.
DTC P0123

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 - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2 
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the TP sensor 1 voltage parameter with a scan tool.
Is the voltage more than the specified value?		 4.5 V Go to Step 5  Go to Step 3 
3 Observe the DTC information with a scan tool.
Did DTC P0223 fail this ignition?		 - Go to Step 5  Go to Step 4 
4
  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 5  Go to Diagnostic Aids
5 
  1. Turn OFF the ignition.
    2. NOTE: DO NOT Use any Mechanical Device Pliers or Screwdrivers to Disengage Connector. Refer to DISENGAGING CONNECTORS NOTICE in Cautions and Notices.
  2. Disconnect the throttle body harness connector. Refer to Throttle Body Assembly Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the TP sensor 1 voltage parameter with a scan tool.
Is the voltage less than the specified value?		 0.1 V Go to Step 6  Go to Step 9 
6 Measure the voltage between the 5-volt reference circuit of the throttle position (TP) sensor and the engine control module (ECM) housing with a DMM.
Is the voltage more than the specified value?		 5.2 V Go to Step 10  Go to Step 7 
7 
  1. Turn OFF the ignition.
  2. Remove the ECM fuse or the PCM/ETC fuse, from the underhood fuse block.
    3. NOTE: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.
  3. Measure the resistance from the low reference circuit of the TP sensor to the ECM housing, with a DMM.
Is the resistance less than the specified value?		 5 Ω Go to Step 12  Go to Step 8 
8 
  1. Install the ECM fuse into the underhood electrical center.
  2. Turn ON the ignition with the engine OFF.
  3. Measure the voltage between the low reference circuit of the TP sensor and the ECM housing, with a DMM. Refer to Circuit Testing in Wiring Systems.
Is the voltage less than the specified value?		 1 V Go to Step 11  Go to Step 14 
9 Test the signal circuit of the TP sensor 1 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 17  Go to Step 13 
10
IMPORTANT: The engine control module (ECM) for this engine is not equipped with 5-volt reference DTCs. The 5-volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5-volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5-volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors.
Test the 5-volt reference circuit of the TP sensor and all shared 5-volt reference circuits 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 17  Go to Step 13 
11
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Test the low reference circuit of TP sensor for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 17  Go to Step 13 
12 Test for shorted terminals and for poor connections at the TP sensor. 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 15 
13 Test for shorted terminals and for poor connections at the ECM. Refer to Circuit Testing and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 17  Go to Step 16 
14
IMPORTANT: The control module and/or the TP sensor may be damaged if the circuit is shorted to battery positive voltage.
Repair the short voltage in the low reference circuit of TP sensor. Refer to Wiring Repairs in Wiring Systems.Did you complete the repair?		 - Go to Step 17  -
15 Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?		 - Go to Step 17  -
16 Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming.
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 - Vehicle in Vehicle DTC Information System OK
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.