Glow Plug Indicator light

[Keith Sparlin]

I have a 2005 Ram with the 5.9 in it . When i head to work in the morning around 12:30 am , After about 15 min of driving the glow plug indicator fomes on and the beep signal comes on . After about 3 min ii goes out , then does it again after 10 min or so of driving . Mind you its around 50 degrees or colder out but driving home when it's a bit warmer it doesn't do it . I have 275,650 miles on it and still runs like a champ . Any idea what would cause this to happen . Do i need a new heater box ? Not sure if it's called that . I know it doesn't have glow plugs in it . Thanks for any help . and Merry Christmas

 

[Oliver Closehauf]

That light is for your grid heater. Here is what chatgpt says:

(I've never heard a beep signal)

When the Grid Heater Energizes​

1. Cold Intake Air Temperature​

The grid heater activates when the intake air temperature is low, typically around:

• Below ~60°F (16°C): Heater may cycle.
• Below ~32°F (0°C): Heater will definitely energize.
• *Colder temps = longer pre-heat time and more post-heat cycling.

Exact thresholds may vary a few degrees between trucks, but these values reflect normal 3rd-gen Cummins operation.

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2. Key-On (Pre-Heat Phase)​

When you first turn the key to RUN (not START):

• ECM checks IAT.
• If cold enough, the grid heater energizes for a few seconds.
• The Wait to Start (WTS) light on the dash illuminates while it’s heating.

Once the WTS light turns off, you can crank the engine.
(Note: The heater may still be energized after the light goes out.)

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3. After Start (Post-Heat Cycling)​

After the engine starts and intake air is still cold, the grid heater can:

• Cycle on and off for 30 seconds–several minutes
• Cycling is based on IAT, coolant temp, and battery voltage
• You may notice:
  • Headlights dimming
  • Voltmeter gauge swinging down when it cycles on

This is normal and helps smooth cold idle and emissions.

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When the Grid Heater Will NOT Energize​

• Intake air temperature is warm enough (typically above ~60°F).
• Battery voltage is too low — ECM protects the electrical system.
• ECM detects a heater solenoid or circuit fault.

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Summary Table​

Condition	Grid Heater Behavior
IAT < ~60°F	May energize briefly at key-on
IAT < ~32°F	Will energize at key-on and cycle after start
Engine running, cold air	Cycles on/off
Warm ambient temp	Does not activate
Low battery voltage	Suppressed by ECM
Faulty relay/solenoid	Suppressed, usually CEL set

 

[Keith Sparlin]

Thanks so much for the reply . I guess this is my situation and the word beep came to mind when writing this . Should of been chimes . Thanks again for the information and Happy Holidays