LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 2004 >> Optra Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - 1.4L DOHC - DTC P1402 To DTC P1661 >> DTC P1512 >> Test Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test Description

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

  1. 6:  This step tests for a high resistance on the ISC motor position sensor 5-volt reference circuit.
  2. 7:  This step tests for a high resistance on the ISC motor high control circuit.
  3. 8:  This step tests for a high resistance on the ISC motor low control circuit.
Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connect End View Reference:  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 DTC information with a scan tool.
Is DTC P0122, P0123, P0222, P0223, or P1511 also set?		 - Go to Diagnostic Trouble Code (DTC) List Go to Step 3 
3
  1. Start the engine.
  2. Observe the ISC motor position sensor parameter with a scan tool while depressing the accelerator pedal.
Does the ISC motor position sensor parameter change when the throttle is open?		 - Go to Step 4  Go to Step 5 
4
  1. Turn OFF the ignition for 30 seconds.
  2. Start the engine.
  3. Operate the vehicle within the Conditions for running the DTC.
Does the DTC fail this ignition cycle?		 - Go to Step 5  Go to Intermittent Conditions
5
  1. Turn OFF the ignition.
  2. Inspect for the following conditions:
    • The throttle body for damage and/or tampering
    • For vacuum leaks
    • For a restricted air intake system
    • For excessive deposits on the throttle plate
    • For excessive deposits in the throttle bore
    • The throttle shaft for binding
    • The throttle linkage or the throttle cable for binding
    • For an incorrectly installed PCV valve and hose
    • For a malfunctioning PCV valve
Did you find and correct the condition?		 - Go to Step 17  Go to Step 6 
6 
  1. Turn OFF the ignition.
  2. Disconnect the throttle body harness connector.
  3. Turn ON the ignition, with the engine OFF.
    4. NOTE: Do NOT use the low reference circuit in the component harness connector for this test. Damage to the control module may occur due to excessive current draw.
    IMPORTANT: Use a test lamp that measures more than 20 ohms for this test.
  4. Connect a test lamp between the 5-volt reference circuit of the ISC motor position sensor and a good ground.
  5. Connect a DMM to the probe of the test lamp and a good ground. Refer to Measuring Voltage Drop in Wiring Systems.
Is the voltage more than the specified value?		 4.8 V Go to Step 7  Go to Step 9 
7 
  1. Connect a test lamp between the ISC motor high control circuit and a good ground.
  2. Connect a DMM to the probe of the test lamp and to battery positive voltage. Refer to Measuring Voltage Drop in Wiring Systems.
Is the voltage more than the specified value?		 0.3 V Go to Step 8  Go to Step 10 
8 
  1. Connect a test lamp between the ISC motor low control circuit and a good ground.
  2. Connect a DMM to the probe of the test lamp and to battery positive voltage. Refer to Measuring Voltage Drop in Wiring Systems.
Is the voltage more than the specified value?		 0.3 V Go to Step 12  Go to Step 11 
9 Test the 5-volt reference circuit of the ISC motor position sensor for 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 14 
10 Test the high control circuit of the ISC motor for 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 14 
11 Test the low control circuit of the ISC motor for 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 14 
12 Test the signal circuit of the ISC motor position sensor for 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 
13 Test for an intermittent and for a poor connection at the throttle body assembly. 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 
14 Test for an intermittent and for a poor connection at the engine control module (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 17  Go to Step 16 
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 Engine Control Module Replacement .
Did you complete the replacement?		 - Go to Step 17  -
17
  1. Clear the DTCs with a scan tool.
  2. Turn the ignition OFF for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC.
Does the DTC fail this ignition?		 - Go to Step 2  Go to Step 18 
18 Are there any DTCs that have not been diagnosed? - Go to Diagnostic Trouble Code (DTC) List System OK
scientia non olet · About LEMON Manuals