GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Chevy K Silverado - 4WD 🢒 Engine 🢒 Engine Controls - 6.6L 🢒 DTC P1643

Circuit Description

A Wait to Start indicator is illuminated by the engine control module (ECM) when the glow plugs are commanded ON. When the ECM is commanding the Wait To Start indicator ON, the voltage potential of the circuit will be low, near 0 volts. When the ECM is commanding the Wait To Start indicator OFF, the voltage potential of the circuit will be high, near battery voltage. The primary function of the ECM is to supply the ground for the Wait To Start indicator control circuit.

Conditions for Running the DTC
    • The ignition is in the ON.
    • The ignition voltage is between 6-18 volts.

Conditions for Setting the DTC

The voltage on the Wait To Start indicator circuit is high, near battery voltage, when the Wait To Start indicator is requested ON.

or

The voltage on the Wait To Start indicator control circuit is low, near 0 volts, when the Wait To Start indicator is requested OFF.

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.

Diagnostic Aids

A faulty bulb or the control circuit shorted to ground will cause a DTC P1643 to set.

Test Description

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

  1. The Wait to Start indicator is illuminated briefly when the ignition is turned ON. The ON time depends upon the temperature of the engine at that time.

    2.

  2. If the fuse opens during this test, there is a short to voltage on the control circuit.

    3.

  3. If no trouble is found in the control circuit or the connection at the ECM, the ECM may be malfunctioning.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Ensure that the engine is not at full operating temperature.
  2. Observe the Wait to Start lamp while turning ON the ignition.

Does the Wait to Start indicator turn ON and then turn OFF?

Go to Step 3

Go to Step 4

3

The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored refer to those tables.

Are additional DTCs stored?

Go to Diagnostic Trouble Code (DTC) List

Go to Diagnostic Aids

4

Does the Wait to Start indicator stay ON?

Go to Step 7

Go to Step 5

5

  1. Disconnect the ECM connector containing the Wait to Start lamp control circuit.
  2. Turn ON the Ignition, with the engine OFF.
  3. Probe the Wait to Start indicator control circuit in the ECM harness connector with a fused jumper connected to a good ground.

Does the Wait to Start lamp illuminate?

Go to Step 6

Go to Step 8

6

Inspect for poor connections at ECM. Repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

7

Inspect the control circuit of the Wait to Start indicator for a short to ground. Repair as necessary. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

8

Check the Wait to Start indicator circuit for the following conditions:

    • An open ignition 1 voltage circuit to the bulb
    • A malfunctioning bulb
    • The control circuit open or shorted to battery voltage

Did you complete the repair?

Go to Step 10

--

9

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 10

--

10
  1. Use a scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 11

Go to Step 2

11

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK