[road rat]

first time ever on here any how here goes
2004 dodge 5.9 cummings starting problem is when pluged in for 2-3 hours in the cold weather it will start other wise it just sits and cranks over already replaced both heater relay switches and still didnt help code on the dash still reads that lower heater relay switch is bad what to do next ?

 

[BigKev12valve]

Make sure your getting power to your heater grid

 

[Broaner]

How cold you talking? It should easily start without the grid down to -10 f. Sounds more like a fuel delivery issue to me. Worn out Cp3's often will have more trouble when cold due to everything being shrunk and fuel leaking back around the plungers

 

[DODGE74]

How many miles in injectors?

Most likely the injectors are worn causing a high return when cold and you end up with a no start. Throw new injectors in it and it fires right up. Seen it many many times.

 

[SilverFox66]

How cold you talking? It should easily start without the grid down to -10 f. Sounds more like a fuel delivery issue to me. Worn out Cp3's often will have more trouble when cold due to everything being shrunk and fuel leaking back around the plungers

if everything is in good shape, it will indeed start fine. I did an experiment with mine last winter. Even during a week long cold spell with highs in single digit (F not C) my truck started fine with my grids unhooked, and no block heater. I wound up hooking the grids back up though. Even though it started fine, it idled rough for s few seconds without them. I didnt like that so I hooked them back up.... idled fine again

 

[Thor99]

x3 on the injectors......I've never seen a common rail that can't start in cold weather NOT plugged in. If your over 150k on the injectors, your on borrowed time.

 

[goalie2]

check your fuel filter and air filter,just to rule them out.Batteries too.

 

[tsijohnston]

Rule of thumb is check the free stuff first. Id definitely look at the batteries and connections. Ive read articles where low or weak batteries will make it difficult for all the electronics to function properly.