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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Optra 🢒 Engine 🢒 Engine Controls - 1.4L DOHC 🢒 DTC P1512

Circuit Description

The idle speed control (ISC) assembly is a throttle body with an integrated motor that is used to control the engine speed at idle. The engine control module (ECM) commands the integrated ISC motor to adjust the throttle angle for idle speed control. The ECM uses a high control circuit and a low control circuit to command the ISC motor. If the ECM detects that the actual ISC motor position can not be commanded to the desired position, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1512 Idle Speed Control (ISC) System

Conditions for Running the DTC
    • DTCs P0222 and P0223 are not set.
    • The engine is running.
    • The ignition 1 voltage is more than 10 volts.
    • The ISC motor angle is between 0.2° and 5.6°.
    • This DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the actual ISC motor position can not be controlled to the desired ISC motor position for more than 5 seconds.

Action Taken When the DTC Sets - European Emissions
    • The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail.
    • The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

Action Taken When the DTC Sets - Non European Emissions

The malfunction indicator lamp (MIL) will illuminate.

Conditions for Clearing the MIL/DTC - European Emissions
    • The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for more than 10 seconds.

Conditions for Clearing the MIL/DTC - Non European Emissions
    • The MIL will turn OFF after the diagnostic runs without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for more than 10 seconds.

Test Description

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

  1. This step tests for a high resistance on the ISC motor position sensor 5-volt reference circuit.

    2.

  2. This step tests for a high resistance on the ISC motor high control circuit.

    3.

  3. 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:
    3. • 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. Notice: 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 Repairsin 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 Repairsin 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