GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Optra 🢒 DTC 🢒 DTC P1511

Circuit Description

The throttle body assembly contains an idle speed control (ISC) motor that is used to control the engine speed at idle. The engine control module (ECM) commands the ISC motor to adjust the throttle angle for idle speed control. An idle switch is also integrated into the throttle body assembly. The idle switch position is dependant upon the position of the throttle. The ECM uses a high and low control circuit to command the ISC motor. If the ECM detects a fault with the ISC motor control circuits or motor, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1511 Idle Speed Control (ISC) Motor Control Circuit

Conditions for Running the DTC
    • The engine is running.
    • The ignition 1 voltage is more than 10 volts.
    • The ISC motor angle is between 0.5-21 degrees.
    • This DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC
    • The ECM detects that the commanded duty cycle is more than 45 percent for 6 seconds.
        OR
    • The ECM detects that the commanded duty cycle is less than -42 percent for 6 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

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 or P0223 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. 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 harness connector of the throttle body.
  3. Probe the high control circuit of the ISC motor with a test lamp connected to a good ground

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 11

6

Probe the low control circuit of the ISC motor with a test lamp connected to a good ground

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 12

7

    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 between 20-30 Ohms.

  1. Probe the high control circuit of the ISC motor with a test lamp connected to a good ground
  2. Measure the voltage from the probe of the test lamp to battery positive voltage.

Is the voltage less than the specified value?

0.3 Volts

Go to Step 8

Go to Step 11

8

    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 between 20-30 Ohms.

  1. Probe the low control circuit of the ISC motor with a test lamp connected to a good ground
  2. Measure the voltage from the probe of the test lamp to battery positive voltage.

Is the voltage less than the specified value?

0.3 Volts

Go to Step 9

Go to Step 12

9
  1. Start the engine.

    2. Important: Do not use the AC millivolt scale on the DMM. This will produce an inaccurate reading.

  2. Measure the frequency in AC Hertz of the high control circuit of the ISC motor to a good ground with a DMM .

Is the frequency within the specified range?

30-40 Hertz

Go to Step 10

Go to Step 13

10

Important: Do not use the AC millivolt scale on the DMM. This will produce an inaccurate reading.

With the engine operating, measure the frequency in AC Hertz of the low control circuit of the ISC motor to a good ground with a DMM .

Is the frequency within the specified range?

30-40 Hertz

Go to Step 15

Go to Step 14

11

Test the high control circuit of the ISC motor for the following:

    • An open
    • A short to ground
    • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

12

Test the low control circuit of the ISC motor for the following:

    • An open
    • A short to ground
    • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 16

13

Test the high control circuit of the ISC motor 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 19

Go to Step 16

14

Important: The engine control module (ECM) may be damaged if the circuit is shorted to battery positive voltage.

Test the low control circuit of the ISC motor 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 19

Go to Step 16

15

Test for shorted terminals and for poor connections 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 19

Go to Step 17

16

Test for shorted terminals and for poor connections 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 19

Go to Step 18

17

Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .

Did you complete the replacement?

--

Go to Step 19

--

18

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 19

--

19
  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 20

20

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