GM Service Manual Online
For 1990-2009 cars only

Refer to

Glow Plug Controls


Object Number: 185292  Size: FS
Cell 10: GAUGES Fuse
Cell 10: ENG-1 Fuse
Cell 10: Battery, and Underhood Fuse Block
Cell 10: Battery, and Underhood Fuse Block
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Powertrain Control Module Connector End Views
Cell 14: G105 (1 of 2)
OBD II Symbol Description Notice
Fuel Controls
Ignition System

Circuit Description

A dash light (Wait To Start) is illuminated by the 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 voltage). The primary function of the PCM is to supply the ground for the Wait To Start lamp circuit.

Conditions for Running the DTC

The ignition switch is in the ON position.

Conditions for Setting the DTC

The voltage on the Wait To Start lamp circuit is high (near battery voltage) when the Wait To Start lamp is requested ON.

or

The voltage on the Wait To Start lamp control circuit is low (near 0 volts) when the Wait To Start lamp is requested OFF.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The PCM will turn the MIL off after three consecutive trips without a fault condition.
    • A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
    • The use of a scan tool.

Diagnostic Aids

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

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

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

  2. If no trouble is found in the control circuit or the connection at the PCM, the PCM maybe malfunctioning, however, this is an extremely unlikely failure.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing any DTCs, use the scan tool Capture Info to save freeze frame and failure records for reference, as the Scan tool loses data when using the Clear Info function.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn the ignition ON leaving the engine OFF.
  2. Using a scan tool, command the glow plug lamp ON and OFF.

Does the glow plug 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 table(s).

Are additional DTC(s) stored?

--

Go to the Applicable DTC table

Go to Diagnostic Aids

4

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector containing the Wait To Start lamp control circuit.
  3. Turn the ignition ON leaving the engine OFF.

Is the 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.

Is the lamp ON?

--

Go to Step 6

Go to Step 8

6

Check the connections at PCM.

Was a repair performed?

--

Go to Step 10

Go to Step 9

7

The Wait To Start control circuit is shorted to ground, repair as necessary.

Is the action complete?

--

Go to Step 10

--

8

Check the Wait To Start circuit for the following.

    • Open ignition feed to the bulb
    • malfunctioning bulb
    • Control circuit open or shorted to B+

Was a repair performed?

--

Go to Step 10

--

9

Replace the PCM.

Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 10

--

10

  1. Using the Scan tool, 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 11

Go to Step 2

11

Does the Scan tool display any additional undiagnosed DTCs?

--

Go to the Applicable DTC Table

System OK