GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Express 🢒 DTC 🢒 DTC P1643

Circuit Description

A dash light, wait to start, is illuminated by the powertrain control module (PCM) when the glow plugs are commanded ON. When the PCM is commanding the wait to start lamp ON, the voltage potential of the circuit will be low, near 0 volts. When the PCM is commanding the wait to start lamp OFF, the voltage potential of the circuit will be high, near battery volts. The primary function of the PCM is to supply the ground for the wait to start lamp circuit.

Conditions for Running the DTC

The wait to start lamp is requested ON, test 1.

or

The voltage on wait to start lamp control circuit is low, near 0 volts, test 2.

Conditions for Setting the DTC

The voltage on wait to start lamp circuit is high, near battery voltage, test 1.

or

The voltage on wait to start lamp control circuit is low, near 0 volts, test 2.

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 number below refers to the step number on the diagnostic table.

  1. Tests the ON and the OFF states. Repeat the command as many times as necessary. When the glow plugs are commanded ON by the scan tool, an internal PCM timer protects the glow plugs from damage by cycling the plugs ON for 3 seconds and OFF for 12 seconds. After the 12 seconds has elapsed, the glow plugs can be commanded ON again.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame/Failure Records for reference. The data in the control module is deleted once the Clear Info function is used.

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. Important: Ensure that both the ON and the OFF states are commanded. Repeat the commands as many times as necessary.

  2. Using a scan tool, command the wait to start lamp ON and OFF.

Does the wait to start lamp turn ON and OFF with each command?

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
  1. Turn OFF the ignition.
  2. Disconnect the PCM connectors.
  3. Turn ON the ignition, with the engine OFF.

Is the Wait To Start lamp OFF?

Go to Step 5

Go to Step 7

5

With a fused jumper wire connected to ground, probe the Wait To Start lamp control circuit in the PCM harness connector.

Does the Wait To Start lamp illuminate?

Go to Step 6

Go to Step 8

6
  1. Check the connections at PCM.
  2. Repair the conditions as needed. Refer to Wiring Repairs in Wiring Systems.

Did you perform a repair?

Go to Step 11

Go to Step 10

7

Repair the Wait To Start control circuit short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 11

--

8
  1. Check the connections at the cluster.
  2. Repair the conditions as needed. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

9

  1. Check the Wait To Start circuit for the following conditions:
    2. • Open ignition feed to the bulb
    • Malfunctioning bulb
    • Control circuit open or shorted to B+
  2. Repair the conditions as needed. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Symptoms - Instrument Panel, Gages and Console in Instrument Panel, Gauges, and Console

10

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 11

--

11
  1. Use a scan tool in order to clear the DTCs.
  2. Start the engine and idle at normal operating temperature.
  3. Select DTC, Specific, then enter the DTC number which was set.
  4. Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic passed?

Go to Step 12

Go to Step 2

12

Does the scan tool display any additional undiagnosed DTCs?

Go to Diagnostic Trouble Code (DTC) List

System OK