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Home >> Chevrolet >> 2005 >> Epica LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - 2.5L (LBK) - DTC P0030 To DTC P0154 >> DTC P0123 >> Test Description

Test Description

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

  1. 2:  This step verifies that a condition exists.
  2. 4:  This step determines whether a condition exists in the idle switch position circuit of the throttle body. If DTC P0223 sets in addition to DTC P0123, repair the idle switch position circuit for a short to battery positive voltage.
  3. 5:  This step tests for a condition in the signal circuit of the TP sensor. If the TP Voltage parameter displays a voltage after the throttle body is disconnected, test for a short to voltage in the signal circuit.
  4. 8:  This step isolates if there is a circuit that is shorted to voltage. Or, if the low reference circuit is open internally or externally of the ECM. If there is no voltage on the low reference circuit after disconnecting the engine coolant temperature (ECT) sensor, test the low reference circuit for an open.
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. Turn ON the ignition, with the engine OFF.
  2. Observe the throttle position (TP) sensor parameter with a scan tool.
Is the voltage less than the specified value?		 4.89 V Go to Step 3  Go to Step 4 
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  Observe the DTC information with a scan tool.
Did DTC P0223 also set.		 - Go to Step 14  Go to Step 5 
5 
  1. Turn OFF the ignition.
  2. Disconnect the throttle body harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the TP sensor 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 TP sensor and the ECM housing with a DMM.
Is the voltage less than the specified value?		 5.2 V Go to Step 7  Go to Step 10 
7
  1. Turn OFF the ignition.
    2. 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.
  2. Measure the resistance from the low reference circuit of the TP sensor to the ECM housing, with a DMM.
Is the resistance more than the specified value?		 10 Ω Go to Step 8  Go to Step 12 
8 
  1. Disconnect the engine coolant temperature (ECT) harness connector.
  2. Turn ON the ignition with the engine OFF.
  3. Measure the voltage between low reference circuit of the TP sensor and the ECM housing.
Is the voltage less than the specified value.		 1 V Go to Step 11  Go to Step 15 
9 Test the signal circuit of TP sensor 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 18  Go to Step 13 
10
IMPORTANT: 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 18  Go to Step 13 
11
  1. Disconnect the ECM harness connectors.
  2. Test the low reference circuit of the 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 18  Go to Step 13 
12 Test for shorted terminals and for poor connections at the throttle body assembly. Refer to Testing for Intermittent Conditions and Poor Connections andConnector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 18  Go to Step 16 
13 Test for shorted terminals and for poor connections at the ECM. 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 18  Go to Step 17 
14
IMPORTANT: The control module and/or the throttle body assembly may be damaged if the circuit is shorted to battery positive voltage.
  1. Turn OFF the ignition.
  2. Disconnect the ECM harness connectors.
  3. Repair the short to voltage in the idle switch position circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 18  -
15
IMPORTANT: The control module and/or the throttle body assembly may be damaged if the circuit is shorted to battery positive voltage.
Repair the short to voltage in the low reference circuit of the TP sensor. Refer to Wiring Repairs in Wiring Systems.Did you complete the repair?		 - Go to Step 18  -
16 Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?		 - Go to Step 18  -
17 Replace the ECM. Refer to Engine Control Module (ECM) Replacement .
Did you complete the replacement?		 - Go to Step 18  -
18
  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 19 
19 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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