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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 P0121 >> Test Description
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Test Description

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

  1. 2:  This step verifies that a condition exists.
  2. 3:  This step determines if the TP sensor voltage is out of range.
  3. 5:  This step tests for high resistance in the 5-volt reference circuit of the TP sensor. If the DMM does not display more than the specified voltage, there is high resistance in the circuit.
  4. 7:  This step tests for high resistance in the low reference circuit of the TP sensor. Test for a condition in the low reference circuit if the resistance is more than the specified value with the ignition OFF.
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 reach operating temperature.
  2. Increase the engine speed to within the specified range for 1 minute.
  3. Observe the DTC Info with a scan tool.
Does the DTC fail this ignition?		 1000-3500 RPM Go to Step 5  Go to Step 3 
3 
  1. Turn OFF the engine.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the TP Sensor voltage parameter with a scan tool.
Is the voltage within the specified range?		 4.15-4.75 V Go to Step 4  Go to Step 5 
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 Intermittent Conditions
5 
  1. Turn OFF the ignition
  2. Disconnect the throttle body harness connector.
  3. Turn ON the ignition, with the engine OFF.
    4. IMPORTANT: Use the J 35616-200  Test Lamp Kit for this test. If the J 35616-200  is not available, use a test lamp that measures more than 20 ohms.
  4. Connect a test lamp between the 5-volt reference circuit of the throttle position (TP) sensor and the engine control module (ECM) housing.
  5. Connect a DMM to the probe of the test lamp and the ECM housing. Refer to Measuring Voltage Drop in Wiring Systems.
Is the voltage more than the specified value?		 4.8 V Go to Step 6  Go to Step 9 
6
  1. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the TP sensor and the signal circuit of the TP sensor.
  2. Observe the TP sensor voltage parameter, with a scan tool.
Is the voltage more than the specified value?		 4.8 V Go to Step 7  Go to Step 8 
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 less than the specified value?		 10 Ω Go to Step 11  Go to Step 10 
8 Test the signal circuit of TP sensor for a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
9 Test the 5-volt reference circuit of the TP sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
10 Test the low reference circuit of the TP sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
11 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 15  Go to Step 13 
12 Test for shorted terminals and for poor connections at the throttle body assembly and 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 15  Go to Step 14 
13 Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?		 - Go to Step 15  -
14 Replace the ECM. Refer to Engine Control Module (ECM) Replacement .
Did you complete the replacement?		 - Go to Step 15  -
15
  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 16 
16 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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