GM Service Manual Online
For 1990-2009 cars only

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 receives an ON signal from the idle switch when the throttle is at idle and receives an OFF signal from the switch when the throttle is open . If the ECM detects a fault with the idle switch, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0510 Idle Speed Control (ISC) Motor Position Sensor Circuit Low Voltage

Conditions for Running the DTC

    • DTCs P0122, P0123, P0222, and P0223 are not set.
    • The ignition is ON, with the engine OFF.
    • The throttle is closed.
    • This DTC runs continuously once the above conditions are met.

Or

    • DTCs P0122, P0123, P0222, and P0223 are not set.
    • The engine is running.
    • The throttle is more than 35 degrees.
    • This DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the idle switch signal is OFF when the throttle is less than 10 degrees for more than 2 seconds.

Or

The ECM detects that the idle switch signal is ON when the throttle is more than 35 degrees for more than 0.2 seconds.

Action Taken When the DTC Sets - European Emissions

    • The malfunction indicator lamp (MIL) will not illuminate.
    • 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.
    • A history DTC is stored.
    • The coolant fan turns ON.

Action Taken When the DTC Sets - Non European Emissions

    • The malfunction indicator lamp (MIL) will not illuminate.
    • The coolant fan turns ON.

Conditions for Clearing the MIL/DTC - European Emissions

    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for 10 seconds.

Conditions for Clearing the MIL/DTC - Non European Emissions

    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for 10 seconds.

Test Description

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

  1. This step checks for a skewed throttle position (TP) sensor. High resistance in the TP sensor circuit can cause this DTC to set.

  2. This step tests for the correct operation of the idle switch within the throttle body . The idle switch is a normally closed switch and the test lamp should illuminate with a closed throttle. The test lamp should go OFF when the throttle is opened.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module 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 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. Turn OFF all accessories.
  3. Observe the throttle position (TP) sensor parameter with a scan tool.

Is the TP sensor percentage less than the specified value?

8 %

Go to Step 4

Go to DTC P0122

4

Observe the idle switch parameter with a scan tool while slowly depressing the accelerator pedal to wide open throttle.

Does the idle switch parameter change when the accelerator pedal is depressed?

--

Go to Step 5

Go to Step 6

5

  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 6

Go to Intermittent Conditions

6

  1. Turn OFF the ignition.
  2. Disconnect the throttle body harness connector.
  3. Install a jumper wire between the low reference circuit of the idle speed control (ISC) motor position sensor harness connector and the low reference circuit of the throttle body.
  4. Connect a test lamp between the signal circuit of the Idle switch at the throttle body and battery voltage.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 11

7

Slowly open the throttle to wide open throttle.

Does the test lamp remain illuminated?

--

Go to Step 11

Go to Step 8

8

  1. Turn ON the ignition, with the engine OFF.
  2. Measure the voltage between the signal circuit of the idle switch and a good ground with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the voltage more than the specified value?

11 V

Go to Step 10

Go to Step 9

9

Test the idle switch signal circuit for an open or for a short to ground. 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

Important: The throttle body assembly or the engine control module (ECM) may be damaged if the circuit is shorted to a voltage source.

Test the idle switch signal circuit 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 15

Go to Step 12

11

Test for shorted terminals and for poor connections at the throttle body. 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 13

12

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 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 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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 16

16

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK