Diagnostic Aids

WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, 2003 Ford Excursion, and 2003 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

The glow plug system is composed of solid state Glow Plug Control Module (GPCM), glow plugs and the associated wiring harness. The glow plug ON time is controlled by the Powertrain Control Module (PCM) and is a function of oil temperature, barometric pressure and battery voltage. The PCM enables the GPCM, which drives the individual glow plugs. Glow plug ON time normally varies between 1 to 120 seconds. In addition to PCM control, the GPCM internally limits the glow plug operation to 180 seconds regardless of PCM commanded ON time. The power to the glow plugs is provided through the GPCM solid state drivers directly from the vehicle battery. The GPCM monitors and detects individual glow plug functionality. The failures detected by the GPCM are passed to the PCM using a serial communication signal on the diagnostic line. This test is only intended to diagnose the following components and circuits:

Glow Plugs
GPCM
Under Valve Cover (UVC) Wiring Harness
Engine & Chassis Wiring Harness
PCM

NOTE: Wait-to-start lamp ON time is independent from GPCM ON time.

CAUTION: Connectors are not interchangeable. The system will generate trouble codes if connectors are mismatched. Make sure the harness green connector is plugged into the module green connector, and the black connector into the black header. There is a black stripe on the GPCM housing for visual verification. The stripe should line up with the black connector. The Powertrain Control Module (PCM) harness connectors must be properly seated and the connector latch properly attached to eliminate possible driveability concerns or a no-start condition. Installing PCM connectors on an angle may cause a bad connection, misdiagnosis and damaged components. Install the connector on where the lever pivots and seats itself. Apply light pressure to get the connector into position on the PCM lever to fully seat the connector.

Glow Plug Test Setup & Procedure - Key On/Engine Off (KOEO) test is performed in order to test and retrieve DTCs stored in PCM memory. Glow plugs are not operated during this test. Glow Plug Monitor Self-Test is a functional Key On/Engine Running (KOER) self-test of PCM performed on-demand with engine running and A/C off. PCM will activate GPCM, which monitors glow plugs. Accelerator pedal may be used to increase engine speed to increase battery voltage, if needed. A fault must be present at time of testing for test to detect a fault. Faults will be sent to PCM on diagnostic line and then output to scan tool.

DTC Descriptions

DTC P0670: Control Line Failure

Fault code will be set when the control circuit is open or shorted to ground or power.

DTC P0671-P0678: Glow Plug Failure(s)

Fault code will be set upon detection of a failed glow plug No. 1 to No. 8 respectively. The code will also be set if an open, shorted to ground, or shorted to power condition occurs anywhere in the circuit.

DTC P0683: Diagnostic Line Failure

Fault code will be set when the diagnostic line is open or shorted to ground or power.

Fig 1: Identifying Glow Plug Control Module Circuits & Components

Courtesy of FORD MOTOR CO.