Section 00-00: Power Stroke Diesel Engine
97-15A 7.3L DI Turbo Workshop Manual
ELECTRONIC CONTROL SYSTEM DIAGNOSTICS

Glow Plug Control

Output Functions

Glow Plug Relay

Controls the current flow to the glow plugs. Glow plug relay "ON" time is controlled by the PCM and is a function of engine oil temperature, barometric pressure and battery voltage. "ON" time normally varies between 10 to 120 seconds. The glow plugs are self-limiting glow plugs and do not require cycling on and off. (The glow plug relay will only cycle on and off repeatedly when there is a system voltage condition greater than 14.5 volts.)

Glow Plug Wait to Start Lamp

Lamp that indicates to the operator when the glow plugs have been on long enough to crank the engine. It is controlled by the PCM. Wait to Start lamp "ON" time is a function of engine oil temperature, barometric pressure and battery voltage. "ON" time normally varies between 1 to 10 seconds. (NOTE: Wait to Start lamp "ON" time is independent from glow plug relay on time.)

Fault Detection/Management

An open or shorted to ground glow plug relay in the control side (coil) or Wait to Start lamp circuit can be detected by an on demand output circuit check performed during the Engine Off Tests.

The glow plug relay (power/switch) side, glow plugs and glow plug harness problems can not be detected by the PCM.

Glow Plug Relay Operation (Voltage Checks)
Test PointsSpecComments
B+ terminal to groundB+Relay switch power, B+ should be present at all times (terminal with single 6 gauge wire). Check connection at starter or fusible links if no power (voltage) present.
Glow Plug Feed to Grd.B+Glow plug feed voltage should be present 10 to 120 seconds after key is cycled on, dependent upon battery voltage, barometric pressure (altitude) and engine oil temperature.
B to GroundB+Relay coil power. Voltage should be present when ign. key is ON - Check fuse if no voltage.
Pin #101 to Ground0v / 12vGlow plug control, switched to (grd) by PCM during operation. 0v = relay ON, 12v = relay off.

Glow Plug and Harness Operation

NOTE: Measure glow plug resistance to ground with the pigtail connector (014-00935) installed at the valve cover connector; then measure resistance from the glow plug feed stud to the harness connector.

Test PointsRelay to Harness ConnectorComments
Glow Plug NumberPigtail Connector to Ground (B-)
Spec< .1 to 2 ohms< 6 ohmsRelay to Harness Connector
NOTE: All engine harness connectors for glow plug/injectors should be disconnected before taking measurements.
High resistance could indicate an open circuit in the engine harness between the glow plug connector and the relay.
#1  Pigtail Connector to Ground B-
High resistance could indicate an open circuit in the UVC (under the valve cover) harness or in the glow plug. Glow plug resistance should measure .1 to 2 ohms dependent upon engine temperature.
#3   
#5   
#7   
#2   
#4   
#6   
#8   

Diagnostic Trouble Code Descriptions
 
0380 = OCC CHK performed by PCM during engine off test. Indicates high or low resistance in GP relay coil circuit.
0381 = OCC CHK performed by PCM during engine off test. Indicates high or low resistance in GP lamp circuit.