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 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 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 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.
-
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.
-
If no trouble is found in the control circuit or in the connection at the PCM, the PCM maybe malfunctioning. This is an extremely unlikely failure.
Step | Action | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||||
Does the glow plug lamp illuminate 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 Aids | |||||||
4 |
Does the lamp illuminate? | Go to Step 7 | Go to Step 5 | ||||||
5 | With a fused jumper wire connected to ground, probe the Wait To Start lamp control circuit in the PCM harness connector. Does the lamp illuminate? | Go to Step 6 | Go to Step 8 | ||||||
6 | Check the connections at PCM. Did you find and correct the condition? | Go to Step 10 | Go to Step 9 | ||||||
7 | Repair the short to ground in the wait to start lamp control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 10 | -- | ||||||
8 | Check the Wait To Start circuit for the following conditions:
Did you complete the repair? | Go to Step 10 | -- | ||||||
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 10 | -- | |||||||
10 |
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? | System OK | |||||||
