Off the top of my head (half asleep)...
The blower speed is not effected by the BCM at all.

The only thing that would cause the fan motor speed to dip is low voltage at the motor.
Notice, I said "at the motor".. that does not mean necessarily the overall system voltage.
If the system voltage were good but the motor speed dips then it would be a problem on the fan circuit itself... (wiring problem causing a voltage drop at the motor).

On the other hand if the overall system voltage dipped, that would do it too.
Doesn't address the other problems though.. I'm only making the point that the fan speed isn't effected by the BCM.

I can't imagine how the three problems could be related unless it's grounding.
But without spending some time in the schematics and grounding diagram I can't imagine where is a ground connection that would effect that combination of problems (fan speed, headlights + dash lamps and airbag indicator.
Not saying there isn't one, but....

There's always the possibility that the three problems are unrelated and only coincidental..
I think you'll need to focus on each problem individually until a clue presents itself.

 

That's what I was thinking, why are 3 different things acting up at the same time. My luck!
Which grounds would you recommend to check? I know there is one on the inner fender that ill clean up. I find the one from the battery to the frame and check that one too. Should i take the light switch on the left side of the dash apart and see how it looks inside?

I know that I put a new blower motor resister in maybe a few years ago because the wiring was melting and loosing connection. Ill double check this and make sure it hasn't happened again.

The only other thing I can think is to get the alternator checked and see if it fails? It does have 237k miles on it.

Is there any way to get the airbag system scanned to see what codes it has thrown? I doubt it will show anything since the light doesn't stay on.

 

You checked the battery voltage at 13.8 and that's good,
But does it remain there at ~13 or is it dipping?

 

Gotta be a ground.... Go to the "How To" section and do some research there....
Hope you find the problem and get it fixed !!!
Keep us posted... Might help other members out !!! LOL

 

I haven't been able to check the voltage when the issues are occurring, but I think the regulator might be going out in the alternator. Do you think this would be causing all the unrelated issues? Its the only thing besides a ground that ties them all together.

 

On these vehicles the voltage regulator is not built into the alternator.
Voltage regulation is performed by the PCM.
There is a charge module also, but it's just a "front end" component that works with the PCM.
It's possible for it to go bad, but I've never heard of one failing. It's a passive device, not much there to fail.

Your first task is to learn if the alternator is keeping the voltage up at it's normal ~ 13 VDC, or if it's drooping sometimes. Thing is, if it fails to keep the battery voltage up then eventually you're gonna see a dead battery. If you aren't seeing dead batteries then the charging circuit is probably OK.

I say "probably" because it's always possible it could let the voltage droop momentarily from time to time. That would be unusual though.

We do know that these trucks' electronics do not tolerate low system voltage very well.
Again though, I would be careful about assuming that all three of the problems you listed are related.

Having an electrical problem come and go at random is the worst, so you do have to look at the clues and symptoms and start with some assumptions.


And the heater fan running slow is one clue, as good a place to start as any.
Just don't be too quick to assume that it's related to the other two problems.
possibilities:
-the fan motor is dying (it does happen that an automotive electrical motor fails intermittently, not all at once).
The fan motor can have shorted windings that happen over time. In that case it may continue to run but the speed will drop (or it will stop altogether) because the motor isn't able to produce full torque.
Bad/worn-out motor bearings can drag down the speed also.

-wiring problem in the fan motor circuit (this includes grounding problems affecting the fan circuit)
-the battery/alternator/charging circuit is allowing the overall system (battery) voltage to droop.


A low voltage problem won't cause the dash lights and the headlights to go out the way you described. If the voltage dropped that far the engine would shut down.
That's where your three problems don't appear to be related...


"Ground problems" are the one thing that can cause problems with two or more (otherwise) unrelated circuits. We say "ground", but that's really not a very accurate word to use... the battery negative circuit has nothing at all to do with the ground, it's just a loose term we've used for years. A better word to use is "common".
It's the common connection for all circuits to the battery negative terminal.

Each separate circuit for all the electrical devices goes through it's own fuse and it's own controls (switch on the dash, sensor, etc), but all those circuits come together at the negative side of the battery, the "common" side.

Because it isn't possible to connect each one of those individual circuits to the battery negative terminal, we connect them to the body/frame in various locations and connect the battery negative to the frame also to complete the circuit(s).

The troubleshooting problem comes when one of those locations develops a problem, if several devices are "grounded" there at the same point. That can cause some really confusing symptoms.

So if all three problems you cited were related, a "ground" problem would be the most likely thing that could cause it.
I would just be careful making the assumption that they are related.

These trucks have gained a reputation around here for "ground problems" only because of the stupid "Splice Packs" under the hood.
Those things are nothing more than a way to shave a few pennies off the cost of assembly at the factory. It was just an idea someone had to make installation of the wire harness go faster on the production-line. Other than that they serve no purpose at all.
Any vehicle can have or develop over time a connection problem to a ground point.

On these trucks though you have the two Splice Packs on either side where the common/ground wire for several circuits come together into one ground connection.
The problem there is not that it's the ground circuit or that it's a multi-pole connection. The problem is that the sort of 'push-on' connector used there has no place on any modern vehicle.
They're only a multi-pole copy of these:

The fact that they are a multi-pole connector used to ground more than one device is what makes the faults they cause confusing.

Again though, I'm not totally convinced that your problem is grounding.. That's for you to discover. The trick of adding a temporary ground wire to the faulty device will answer that question.

.

 

I think you have at least two or maybe three issues but all have simple fixes.
1. Bad resistor/connector/or wiring at the hvac blower.
2. Bad battery cable or ground connections. Be sure to clean the ground junction between air filter box & rt. inner fender.
3. Failing battery. If it's bad consider upgrading to a larger group 65 battery which is usually cheaper and will fit perfectly if you discard the battery enclosure.

 

Do you have any aftermarket electronic components installed in the truck i.e. head unit, amp, remote start. Do you keep anything plugged into the OBD port, such as a ScanGauge?

Did all of these issues originate about the same time?

The SIR (airbag) light is controlled by the Sensing and Diagnostics Module using the Serial Data bus, so it doesn't appear that a defective ground would be the cause of that issue.

How old is the battery? Have you had it load tested? I'm pretty sure that checking battery voltage with the engine running is only going to get you the charging voltage.

 

...
How old is the battery? Have you had it load tested? I'm pretty sure that checking battery voltage with the engine running is only going to get you the charging voltage.

With the engine running, that's the system voltage:
(Battery & Alternator) * the charge regulation

His problems are happening with the engine running, so that's the voltage the airbag control unit and the fan motor and the lights are seeing.... assuming that is, the circuit for each is not faulted and is delivering the current to the device without a significant voltage-drop.

Charging voltage is above 13 volts.... should be near 14.
Normal system voltage is a nominal 12 to 13 volts.
Running system voltage is maintained by the alternator (under command of the charge regulation circuit), not the battery.


Charging voltage happens when the battery needs to be topped-off just after startup.
The system voltage should soon drop to about 13 in a few minutes when the battery is fully recharged.
(unless you were sitting with the audio or lights on, then it'll be a little longer)

The condition of the battery only becomes an issue as it deteriorates and can no longer accept a full charge.
If that continues far enough then the alternator may no longer be able to keep up (if the battery has a shorted cell for example and is gulping down a bunch of current pumping it through that shorted cell).
The running voltage may droop then..
But chances are it's already left you unable to start up by then and you will have replaced it.

So if the battery becomes so deteriorated that it drains a huge load of current then it'll drag down the voltage.
Otherwise, even if the battery is old and weak, (assuming you do get the engine up and running) the alternator will maintain the voltage at normal (~12 - 13 vdc).

 

I had similar issues a few months ago, and it turned out to be a loose grounding point in my engine bay.

Pop your hood and check the ground on the Driver Side quarter panel.

 

The only way to effectively troubleshoot this is to separate the three problems and focus on each one individually.
If you do find then that they're all somehow related then so be it, but you won't get there by guessing.. not with that list of different unrelated devices/components.

I don't know anything about the airbag circuit at all, so I'm gonna put that aside for a moment and defer to Cart there.

One problem of course is that all three problems are intermittent.
Troubleshooting an intermittent electrical problem is tough, whether vehicle wiring or house wiring or whatever else.

With regard to grounding problems....
If you have problems with one or more devices and you suspect a possible grounding problem, you can easily test for this and eliminate it by adding an additional ground wire from the battery ground point directly to the device that exhibits the problem.

This is simple and quick to do and costs almost nothing.
It can be as simple as a temporary jumper wire from the battery to the device, or it can be a permanently-installed wire to make the ground connection to the load (motor, solenoid, light, whatever).

If connecting an additional temporary ground wire to the device cures the problem then you know the problem is in the ground-side circuit, somewhere.
You can then chose to either hunt for the cause (corrosion somewhere, loose connection, whatever) or you can just install the new ground wire permanently.
Nothing wrong at all with having two "ground" paths, so there's no need be concerned with cutting or eliminating the original ground-side connection... just connect the new additional wire, make a good ground connection on the opposite end at or near the battery and you're done.


This works if the device being powered has a negative-side ("ground") wire going off somewhere to be "grounded" (like in one of the two SplicePacks).
It also works if the device does not have a negative wire, but "grounds" directly to the sheet-metal where it's mounted.

And there's nothing at all wrong with adding a permanent ground wire to any devices that do connect just through their sheet-metal mounting. I would recommend it in fact.

Notice that on the heater/AC fan the "ground" is from the speed switch, not at the motor.
The motor negative-side connection is from the motor to the switch, and one terminal of the switch then goes to "ground". (see the schematic)..
I don't know where that connection is, but in a pinch you can do the same trick of running a new separate ground wire, except in this case you would connect it at that point where the black wire leaves the switch (not at the motor).

 

I really appreciate all of the input you guys have given me. Way more than I thought I would get!! :salute:

The truck doesn't have any aftermarket electrical at all except a head unit.

I actually took the alternator off today and brought it to get tested, and guess what? It failed. Only was putting out about 11.0v.

So I put on a new alternator and checked some of the grounds under the hood. The battery is only about 2 years old I believe.

Ill drive the truck over the next few days and see what happens. These issues have only started up over the past few days so I am hoping that the alternator started to slowly go out and that's what caused these issues. We shall see and I will keep you updated on what happens.

 

If the alternator was getting that weak then there's a good chance you've nailed it.

It would have left you on the side of the road soon enough anyway... you got an early warning.

 

Hope you'll come back with a report on this when you know for sure that it's OK.

Who tested the alternator for you and what did they use to test it?
And what is the running voltage now?

 

So far so good, no problems at all!
Had it tested at AutoZone. I watched as he tested it, and we ran it 4 times. Each time it failed with a low voltage of about 11.2.
So far it has been putting out a steady 14.1-14.3 volts without any drops.

Will keep you updated if something changes, thanks again for all the help!