GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Optra 🢒 Engine 🢒 Engine Controls - 1.6L (L91) 🢒 DTC P1661

Circuit Description

The malfunction indicator lamp (MIL) is located on the instrument panel cluster. The MIL will illuminate when there is an emission related failure or the ignition is ON with the engine OFF. Ignition 1 voltage is supplied to the MIL. The engine control module (ECM) turns the MIL ON by grounding the control circuit of the MIL using a low side driver. The ECM monitors the voltage level on the control circuit of the MIL. If the ECM detects an open or short to ground on the control circuit of the MIL, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1661 Malfunction Indicator Lamp (MIL) Control Circuit Low Voltage

Conditions for Running the DTC
    • The ignition is ON or the engine is operating.
    • The DTC runs continuously once the above condition is met.

Conditions for Setting the DTC

The ECM detects an open or short to ground on the control circuit of the MIL.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will 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.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault.
    • Using the scan tool can clear DTCs.
    • Disconnect the ECM battery feed for 10 seconds.

Test Description

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

  1. This step tests the control circuit for a shorted to ground.

    2.

  2. This step tests the control circuit for an open.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connect 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. Clear the DTC with a scan tool.
  3. Wait 30 seconds.

Does DTC P1661 set?

--

Go to Step 3

Go to Step 4

3

Is DTC P0656 set?

--

Go to Step 15

Go to Step 5

4
  1. Turn OFF the ignition for 30 seconds.
  2. Operate the vehicle within the Conditions for Running the DTC.

Did the DTC fail this ignition?

--

Go to Step 5

Go to Intermittent Conditions

5

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM).
  3. Turn ON the ignition, with the engine OFF.

Does the MIL illuminate?

--

Go to Step 14

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Connect a 3-ampere fuse jumper wire from the control circuit of the MIL at the ECM harness connector terminal to a good ground.
  3. Turn ON the ignition, with the engine OFF.

Does the MIL illuminate?

--

Go to Step 13

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Remove the IPC. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit of the MIL with a test lamp connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 15

8

  1. Connect a 3-ampere fuse jumper wire from the control circuit of the MIL at the ECM harness connector terminal to a good ground.
  2. Probe the control circuit of the MIL at the IPC harness connector with a test lamp connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 14

9
  1. Turn OFF the ignition.
  2. Disconnect the CLUSTER fuse in the Instrument Panel (I/P) Fuse Block.
  3. Measure the resistance of the ignition 1 voltage circuit of the MIL from the fuse terminal to the IPC harness connector terminal.

Is the resistance less than the specified value?

3 ohms

Go to Step 10

Go to Step 14

10

Measure the resistance of the control circuit of the MIL from the ECM harness connector terminal to the IPC harness connector terminal.

Is the resistance less than the specified value?

3 ohms

Go to Step 11

Go to Step 14

11
  1. Remove the MIL lamp from the cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.
  2. Measure the resistance of the lamp

Is the resistance within the specified range?

10-18 ohms

Go to Step 12

Go to Step 16

12

Test for shorted terminals and poor connections at the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 17

13

Test for shorted terminals and poor connections at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

14

Repair the control circuit of the MIL for one of the following conditions:

    • An open
    • A short to ground
    • High resistance

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

15

Repair the ignition 1 voltage circuit of the MIL for one of the following conditions:

    • An open
    • A short to ground
    • High resistance

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

16

Replace the MIL lamp. Refer to Instrument Cluster Bulb Replacement in Instrument Panel, Gages and Console.

Did you complete the replacement?

--

Go to Step 19

--

17

Replace the IPC. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.

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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 20

20

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK