Diagnostic Aids

WARNING: This page is about a different variant/trim than selected.

NOTE: After each service or repair procedure has been completed, reconnect all components. Clear DTCs and repeat QUICK TEST procedures to ensure all electronic engine control systems are working properly and DTCs are no longer present.

This test is for models with California emissions only. Perform this test when directed by QUICK TEST or SYMPTOM DIAGNOSIS in TROUBLE SHOOTING - NO CODES - 7.3L DIESEL article. The glow plug system is composed of solid state Glow Plug Control Module (GPCM), glow plugs and associated wiring. Glow plug "on" time is controlled by Powertrain Control Module (PCM) and is a function of engine oil temperature, barometric pressure and battery voltage. WAIT TO START light "on" time is independent from GPCM glow plug "on" time. PCM enables GPCM, which drives individual glow plugs. Glow plug "on" time varies between 1-120 seconds. In addition to PCM control, GPCM internally limits glow plug operation to 180 seconds regardless of PCM commanded "on" time. Power to glow plugs is provided though GPCM solid state drivers directly from battery. Failures detected by GPCM are passed to PCM using a serial communication signal. 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

CAUTION: GPCM connectors are not interchangeable. If connectors are mismatched, a DTC will be generated. Ensure Green harness connector is plugged into Green GPCM connector, and Black harness connector is plugged into Black GPCM connector. Black stripe on GPCM housing should align with Black harness connector.

WARNING: DO NOT perform voltage checks with engine running. Injector Driver Module (IDM) supplies 115 DC volts to all fuel injectors. DO NOT pierce injector wiring harness, severe electrical shock may occur.

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.

Fig 1: Identifying Glow Plug Control Module Circuits & Components

Courtesy of FORD MOTOR CO.