GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series Motorhome (Cutaway) C4/C5 🢒 DTC 🢒 DTC P1643

Circuit Description

The wait to start indicator illuminates in the message center when the engine control module (ECM) commands the glow plugs ON. The ECM provides the ground for the wait to start indicator control circuit. The ECM monitors the voltage on the control circuit in order to determine if there is a circuit malfunction. The ECM should detect a low voltage when the indicator is illuminated and a high voltage when the indicator is not illuminated.

Conditions for Running the DTC
    • The ignition is in ON.
    • The ignition voltage is between 9-16 volts.

Conditions for Setting the DTC
    • The ECM detects a lower than normal voltage at the control circuit of the wait to start indicator when the ECM commands the indicator to illuminate.
    • The ECM detects a higher than normal voltage at the control circuit of the wait to start indicator when the ECM is not commanding the indicator to illuminate.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic test fails.
    • The ECM records the operating conditions at the time that the diagnostic test fails. The first time the diagnostic test fails, the control module stores the information in the failure records. If the diagnostic test 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 condition to the Freeze Frame and updates the failure records.

Conditions for Clearing the DTC/MIL
    • A current DTC clears when the diagnostic test runs and passes.
    • The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic test passes.
    • The DTC becomes history when the conditions for setting the DTC are no longer present.
    • The history DTC clears after 40 malfunction free warm-up cycles.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • The DTC may be intermittent. For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • If any additional DTCs are stored, refer to
       -  Diagnostic Trouble Code (DTC) List in Engine Controls - 6.6L (LB7).
       -  Diagnostic Trouble Code (DTC) List in Engine Controls - 6.6L (LLY).
       -  Diagnostic Trouble Code (DTC) List in Engine Controls - 7.8L.

Test Description

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

  1. The wait to start indicator illuminates briefly when the ignition is turned ON. The ON time depends upon the temperature of the engine at the time.

    2.

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

Step

Action

Yes

No

Schematic Reference: Driver Information System Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Instrument Cluster Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

2

  1. Ensure that the engine is not at full operating temperature.
  2. Turn the ignition ON.
  3. Observe the wait to start indicator in the message center.

Does the wait to start indicator illuminate and then turn OFF?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Does the wait to start indicator illuminate continuously in the message center?

Go to Step 6

Go to Step 4

4

Does the wait to start indicator not illuminate in the message center with the ignition ON?

Go to Step 5

Go to Diagnostic Aids

5

  1. Turn the ignition OFF.
  2. Disconnect the engine control module (ECM) connector C2.
  3. Connect a 3-ampere fused jumper wire between the wait to start indicator control circuit and a good ground.
  4. Turn the ignition ON, with the engine OFF.

Does the wait to start indicator illuminate in the message center?

Go to Step 10

Go to Step 7

6
  1. Turn the ignition OFF.
  2. Disconnect the ECM connector C2.
  3. Observe the wait to start indicator in the message center.

Does the wait to start indicator illuminate in the message center?

Go to Step 8

Go to Step 10

7

Test the wait to start indicator control circuit for an open, for a short to voltage or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Test the wait to start indicator control circuit for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

9

Inspect for poor connections at the harness connector of the message center. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

10

Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

11

Replace the message center. Refer to Telltale Circuit Board Replacement .

Did you complete the replacement?

Go to Step 13

--

12

Important: Program the replacement ECM.

Replace the ECM. Refer to:

    •  Engine Control Module Replacement in Engine Controls - 6.6L (LB7).
    •  Engine Control Module Replacement in Engine Controls - 6.6L (LLY).
    •  Engine Control Module Replacement/Restore Fuel Rate Data in Engine Controls - 7.8L.

Did you complete the replacement?

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

Go to Step 2

System OK