Pinpoint Test R: Glow Plug Indicator: Description

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1996 Ford RV Cutaway, 1996 Ford Pickup, 1996 Ford F-Super Duty, 1996 Ford Econoline, and 1996 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.

Glow plug relay controls current flow to glow plugs. Glow plug relay ON time is controlled by Powertrain Control Module (PCM) and is a function of engine oil temperature, barometric pressure and battery voltage. Glow plug ON time is 10-120 seconds. Glow plug WAIT TO START light indicates to operator when glow plugs have been on long enough to crank engine. It is controlled by PCM. WAIT TO START light ON time is a function of engine oil temperature, barometric pressure and battery voltage. ON time normally is 1-10 seconds.

NOTE: WAIT TO START light ON time is independent from glow plug relay ON time.

An open or shorted to ground glow plug relay or WAIT TO START light circuit can be detected by performing a KOEO OUTPUT STATE SELF-TEST. See KOEO OUTPUT STATE SELF-TEST under QUICK TEST.

Perform this test when directed here by QUICK TEST. This PINPOINT TEST is intended to diagnose:

Warning light.
Wiring harness circuit; (WAIT TO START light).
Powertrain Control Module (PCM).

NOTE: Glow plug and glow plug wiring harness problems cannot be detected by PCM.

Fig 1: Glow Plug & Glow Plug Lamp Circuit Schematic

Courtesy of FORD MOTOR CO.

Fig 2: Identifying Glow Plug Warning Light Circuit

Courtesy of FORD MOTOR CO.

WARNING: DO NOT perform any voltage checks with engine running. 115-volts DC at 10 amps is present on injector circuits. Personal injury may result if proper procedures are not followed.