S: Glow Plugs and Relay
Introduction
Introduction
1994 PCED OBDI-A | SECTION 18A: Diesel Diagnosis — 7.3L DI Engine |
S: Glow Plugs and Relay Introduction | S: Pinpoint Tests |
Glow Plug Relay — relay that 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.
Glow Plug Wait Lamp — a light intended to indicate to the operator when the glow plugs have been on long enough to crank the engine. Wait light ON time is a function of engine oil temperature, barometric pressure and battery voltage. ON time normally varies between 2 to 10 seconds. Note: Wait light ON time is independent from glow plug relay ON time.
An open or shorted to ground glow plug relay or wait lamp circuit can be detected by an on demand output circuit check performed during the KOEO test.
Glow plug and glow plug harness concerns cannot be detected by the PCM.
Do not perform any voltage checks with the engine running 115 v DC at 10 amps present on injector circuits.
| Test Points | Spec. | Comments |
|---|---|---|
| B+ terminal to Ground | B+ | B+ should be present at all times (terminal with single 6 gauge wire); check connection at starter or fusible link if no power present. |
| Glow Plug Feed to Ground | B+ | Voltage should be present 10 to 120 seconds after key cycled on, dependent upon battery voltage, barometric pressure (altitude), and engine oil temperature. |
You should enter this pinpoint test only when directed here from the symptom flow charts.
This pinpoint test is intended to diagnose only the following:
The glow plug relay control signal is used to control a relay to cycle the glow plugs for assisting engine start-up. Glow plugs will be operated at low ambient temperature and/or high altitude. The engine oil temperature (EOT), battery voltage (IVPWR), and barometric pressure (BARO) are used to control the glow plug relay. At colder temperatures, the plugs are on longer. At high battery voltage the duty cycle is reduced to prevent plug damage. For low barometric pressure, the ON time is extended to assist start/drive-away.
| S: Pinpoint Tests |