Glow plug light wont go out

glow plugs dont last for ever
have them visually inspected

they need to heat up to spec or motor wont start

what motor or vehicle ?

THIS COMES ALL FROM "WAIT TO START" DO YOU WAIT TO START? IF NOT,THEN THE GLOW PLUGS ARE BUR'NT OUT,WHICH YOU WILL NOT NEED UNTIL FALL. OR MAYBE YOU'VE GOT IT HOOKED ON EITHER,STARTING FLUID,IN WHICH CASE,I SUGGEST YOU REPLACE THOSE GLOW PLUGS NOW.OR ELSE YOU'RE MOVING ON TO EVEN WORSE ISSUES.LET ME ASK YOU THIS,WHY ARE'NT THE GLOW PLUGS BEING DENIED POWER? AFTER ALL THEY START THE ENGINE? AFTER YOU INSERT THE KEY INTO THE SWITCH,WAIT TO START,LIGHTS UP.IF YOU'VE NOT WAITED UNTIL THAT WAIT TO START LIGHT GOES OFF,,,YOU'VE BURNT THE GLOW PLUGS UP.THE ONLY THING TO DO IS REPLACE THEM ALL.IF YOU'VE BEEN USING STARTING FLUID OR EITHER TO START YOUR ENGINE FOR A LONG PERIOD OF TIME,FORGET REPLACING THE GLOW PLUGS,BECAUSE YOUR ENGINE IS ADDICTED TO THE BOTTLE(EITHER) YOU MAY BE ONE OF THE LUCKY ONES,REPLACING THE GLOW PLUGS MAY RESOLVE YOUR ISSUES.BUT,WAIT TO START,,AIN'T NO JOKE. BEST OF LUCK TO YOU & YOURS!

The code P0674 tells you that something in the glow plug circuit is faulty causing the glow plug on cylinder #4 to fail to heat up. The entire circuit must be checked to locate the fault.

Symptoms With just one glow plug failure other than the check engine light coming on, the symptoms will be minimal since the engine will normally start with one bad plug, under freezing conditions you would be more likely to experience hard starting.

Potential Causes The causes for this DTC may include: Faulty cylinder #4 glow plug Open or shorted glow plug circuit Damaged wiring connector Faulty glow plug control module Diagnostic Steps & Possible Solutions You will need a digital volt ohm meter (DVOM) for the complete test.
Continue through the tests until the problem is confirmed. You will also need a basic OBD code scanner to reset the computer and erase the code. Check the cylinder #4 glow plug by disconnecting the wire connector on the plug. Place the DVOM on ohms and place the red lead on the glow plug terminal and the black lead on a good ground. The range is .5 to 2.0 ohms, if it is out of range replace the glow plug.

have you had the glow plugs checked or replaced? the engine light'wait to start is not a joke. it means the engine glow plugs need time to heat the cylinders to max. heat to fire the engine to start. if you use either or strting fluid to start the engine in cold weather,be careful,the motor will get addicted to the starting fluid. sounds like you've not waited on the wait to start light goes off before cranking the engine.replace the glow plugs 1st and then wait before the wait to start light goes off! it's a common mistake.however the cost of glow plug replacement will be a constant reminder to wait to start. glow plugs cost about $100.00 plus labor.been there myself!! you can start engine easily in a/m with either or regular starting fluid, but please take this to heart,it's easier to replace glow plugs,than engine you can use starting fluid by spraying into the air intake of motor once,twice, but from there on,you're on your own! thank you for choosing fixya.com

Hello philkatkiele: My name is Roger and I will help you. First thing you need to check is the glow plugs. They will need tested individually. Un plug all 8 glow plugs. Take a test light and hook end to the positive battery cable. Touch opposite end of test light to the terminal end of the glow plug. The test light should light. Touch all 8 glow plugs. Ant that do not light are bad and will need replaced. If glow plugs are burnt out then the controller will flash wait light to early or very fast. The wait light should be on for approximately 10 seconds.If al glow plugs check ok then I would suspect the glow plug controller as the problem. Also if the temperature out side is below 40 degrees the truck should be plugged in. This will help to make the engine start easier. Should you need further help please just ask.Please rate the answer as this way I know it was helpful. Thank You for using Fix Ya. Roger

The wait to start light always comes on for at least 1 sec, if it goes off early it must think the engine is warm.

My guess is you have a faulty engine oil temp sensor that is telling the pcm that it is already warm. The only way to know for sure is to read the info with a scan tool.

Glow Plug System: Description and Operation
GLOW PLUG SYSTEM
The 6.0L diesel engine uses a glow plug system that preheats air in the combustion chamber to improve cold engine starting.
The system consists of:
- glow plugs.
- glow plug control module.
- powertrain control module (PCM).
- engine oil temperature (EOT) sensor.
- barometric pressure sensor (BARO sensor).
The glow plug monitor system is part of the On-Board Diagnostics II (OBD II) System.
The glow plug system is electronically controlled by the powertrain control module. If the oil temperature is below 55°C (131°F) the powertrain
control module will energize the glow plugs immediately after the key is placed in the ON position. Then, depending on the readings from the engine
oil temperature (EOT) sensor and the barometric pressure (BARO) sensor, the powertrain control module determines how long the glow plugs will be
on.
The glow plugs are located in the cylinder heads, under the glow plug buss bar.
The glow plugs are self-regulating. If the engine oil temperature is above 55°C (131°F), the powertrain control module will bulb-check the WAIT TO
START lamp but not energize the glow plug relay.
The glow plug ON time varies from 0-120 seconds depending on battery voltage, engine oil temperature and barometric pressure.
The glow plug control monitor (GPCM) system is designed to find failed glow plugs or failed wiring in the glow plug system.

The problem is the glow plugs are bad or not coming on. Even though the "wait to start" light comes on, the glow plugs may not come on. I have found when this happens, the light comes on for only 1-2 seconds and goes off. With the engine cold, the light should stay on for about 5 to 7 seconds. The colder the engine, the longer the plugs should stay on. There is one glow plug for each cyl. The plugs are in the "V" of the engine and screwed into head. Only one wire goes to the glow plug and the wire runs from one plug to the next on each bank. You test them by removing them and grounding the body and putting 12v positive to the terminal. The tip should glow red hot like a cigarette lighter. There is a glow plug relay behind the air intake horn which also could be the problem and there is a engine temp sensor in the circuit also.

This may not person to your question. A friend familiar with diesels takes out the automatic electric timed feed to the glowplugs, installs a manual momentary switch to energize the glow plug warm up power. His theory is timer problems, to eliminate the timer and use the glow plug manually.

if you need connectors and terminals for the glow plug connections under the valve cover, Ford sells then so you don't need a whole $600 harness.

info for your use

Section 03-07B: Glow Plug System 1996 F-250, F-350, F-Super Duty Equipped with 7.3L Diesel Engines Workshop Manual
DESCRIPTION AND OPERATION Glow Plug System The 7.3L diesel engine uses a glow plug system which preheats air in the combustion chamber to improve cold engine starting. The system consists of eight glow plugs, the glow plug control module (12B533), powertrain control module (PCM) (12A650), engine oil temperature (EOT) sensor and barometric pressure sensor (BARO sensor) (12A644). The glow plug system is electronically controlled by the powertrain control module. The powertrain control module energizes the glow plugs immediately after the key is placed in the ON position and then determines how long the glow plugs will be on according to the engine oil temperature and the barometric pressure. The required time for the glow plugs to be energized decreases as the engine oil temperature and barometric pressure increase. The glow plugs are self-regulating, and the powertrain control module controls relay ON time. The powertrain control module protects the glow plugs by energizing them for short durations if the battery voltage is abnormally high.

Possible Causes: Insufficient glow plug ON time will not allow enough heat to accumulate in the combustion chamber to easily facilitate starting. If the glow plug system ON time does not meet any of the specifications in the accompanying chart the problem is most likely a faulty wire harness connection, ground connections or glow plug relay.

If the glow plug resistance to ground is high, the most likely causes are an open UVC (under valve cover) harness or open glow plug.
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Relay Operation
Install a DVOM on the glow plug feed side of the glow plug relay (large stud with two wires connected). Turn the ignition key to the ON position but do not attempt to start. Note the time in seconds from when the key is turned on and the glow plug relay energizes until the glow plug relay de-energizes. The glow plug relay makes a loud click noise which is easily heard when it energizes and de-energizes. The dome light will dim and the dash voltmeter will dip when the glow plugs are drawing current from the battery. Compare the times measured to the table (time will be affected by engine temperature, battery condition and vehicle altitude). The voltage at the glow plug feed terminal may vary from 9 to 12 volts depending upon battery condition.
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If battery voltage not present check for B+ at power supply terminal (terminal with single large wire). Power for glow plug power supply is supplied from starter relay through two fusible links at solenoid.
Glow Plug Operation
Disconnect all of the glow plug/injector harness connectors from the valve cover gaskets. With the pigtail installed, measure glow plug resistance to ground (preferably B-). A resistance measurement of .1 to 6 ohms indicates a good glow plug.



Glow Plug Harness Continuity
Measure for continuity from the connector harness to the glow plug feed terminal on the glow plug relay. Resistance should be less than 5 ohms.
Incorrect measurements will result if all glow plug/injector connectors to valve cover are not disconnected.

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Glow Plug Relay The glow plug relay (12A343) has a plastic base and two mounting bolts. It is operated by the powertrain control module (PCM) (12A650) which senses engine oil temperature, PCM voltage and barometric pressure. When the engine oil temperature or the barometric pressure is low, the PCM activates the glow plug relay and the glow plugs. If the PCM voltage is too high, the powertrain control module deactivates the glow plug relay and the glow plugs immediately energize for a shorter duration, decreasing the modulation of the duty cycle.
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Glow Plug Removal

1. WARNING: THE RED-STRIPED WIRING HARNESS CARRIES 115V DC. SEVERE ELECTRICAL SHOCK MAY BE RECEIVED. DO NOT PIERCE.
   Remove valve cover (6582). Refer to Section 03-01D .
   

1. Disconnect glow plug electrical connector using a pair of pliers.
   

1. Remove glow plug using 10mm socket.
   

1. Clean and inspect glow plug tip for damage. Replace if damaged.
   

Installation

1. Install glow plug and tighten to 19 Nm (14 lb-ft).
   

1. Connect glow plug electrical connector. Make sure glow plug wiring is routed to avoid moving parts.
   

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Glow Plug Control Glow plugs are used to warm the cylinders to improve cold-engine starting. The PCM uses the engine oil temperature (EOT) sensor and barometric pressure (BARO) sensor to determine how long the glow plugs will be on. The PCM energizes the glow plugs longer if the engine is very cold or if the barometric pressure is low at high altitudes.
The PCM controls the relay that supplies power to the glow plugs with the glow plug control (GPC) signal. When the GPC signal is grounded by the PCM the relay closes, turning the glow plugs on.
The glow plugs are controlled by the following sequence:

1. PCM energizes the glow plugs.

1. The PCM energizes the glow plugs immediately after the ignition is placed in the ON position.

1. The PCM then determines how long glow plugs will be on based on EOT sensor and the BARO sensor. The required time to warm up the cylinder decreases the engine oil temperature and barometric pressure increases at low altitudes.

Glow Plug Lamp Control The glow plug lamp (GPL) signal controls the WAIT TO START light located on the instrument panel. This light is used to indicate when to start the engine. The cylinders are being warmed by the glow plugs during and after this light is lit. The PCM energizes the glow plug lamp longer if the engine is very cold or if the barometric pressure is low.
When the GPL signal is brought low, the "Wait to Start" lamp is turned on.
The glow plug lamp is controlled by the following sequence:

1. PCM lights the WAIT TO START light after a key on reset occurs.

The PCM determines the glow plug lamp activation time based on engine oil temperature, barometric pressure and battery voltage.

1. PCM turns off the WAIT TO START light.

The glow plug lamp is turned off when the timer counts to the number of seconds specified by the PCM. The glow plugs will normally remain on longer than the "Wait to Start" lamp.
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HAVE YOU REPLACED ALL YOUR GLOW PLUGS RECENTLY? EVEN THOUGH THE GLOW PLUGS APEAR TO BE WORKING I FIND WITH AGE THEY NO LONGER HEAT UP QUICKLY ENOUGH BEFORE CONTROLER TIMES OUT. THEREFOR CREATES A HARD OR NO START CONDITION.