Silverado Draining Battery – GM Mechanics advice

Jumpstarting isn’t the best way to start your day, and so today, we are going to nail this battery drain problem. I’m a GM mechanic, and we’ll walk this road together.

The most common cause of Chevrolet Silverado battery drain is a failing battery. A faulty alternator and a short caused by poor accessory installation are the next most likely causes.

In this post, you’ll learn how to test your battery and alternator; you’ll learn how to quickly find the source of your Silverado battery drain and how you can fix it.


Common Battery Drain Causes

Battery drains are a pain, no doubt, and as a mechanic with over twenty-five years of experience, I’ve found battery drains are often caused by a failing battery, common causes include:

  1. Failing battery
  2. Faulty alternator
  3. Poor accessory wiring

Let’s deal with the battery drain first, giving it’s the most likely culprit.

1 Failing Battery

Batteries don’t last forever; that said, they do last longer today than batteries of old, which is thanks in part to a control module that is tasked with managing your battery. It monitors your battery health and temperature and optimizes alternator output.

But even with this technology, batteries fail. And Silverado’s, like all modern trucks, rely heavily on battery power to run control module systems, meaning your Silverado is a power-hungry beast; a strong battery is critical.

Your battery itself may be in the early stages of failure. This commonly happens as the weather turns a little colder. That said, there may be other reasons your battery isn’t doing its job. They include loose or dirty battery terminals, so we must first eliminate them as possible reasons your battery isn’t doing its job.

The easiest way to eliminate the battery as your source of battery drain is to test it, and we’ll cover that below.

Battery Testing

Before testing your battery, we’ll need to first check the battery terminals are clean and tight. If the battery terminals are dirty (white crusty build-up), this is a sign of battery sulfating and should be replaced. 

Sulfating is dangerous as the battery is venting hydrogen gas which is combustible when offered an ignition source. It also means the battery is at the end of its life.

The process of checking the terminals is as follows:

  • Use disposable gloves (acid burns the skin)
  • Pop the hood
  • Check the negative terminal by giving it a twist
  • Check the positive terminal by giving it a twist
  • If loose or give them a tighten

With loose and dirty terminals eliminated, it’s now time to test the battery itself. 

Testing the battery is a two-step process. 

Step one – Check battery voltage.

Step two – Crank test

Step one

A battery must have at least 12.5 volts to test successfully. And so, in step one, we’ll need to check battery voltage is above 12.5v.

The process is as follows:

  • Engine off and ignition off
  • Voltmeter set to 20 v Dc
  • Place the red probe on the red positive battery pole and the black probe on the negative battery pole
  • Read the meter and check against the table below
Voltage% ChargedRecommend
12.7 – 13.2100%Ok
0 – 11.90%Charge

If your battery is below 12.5v, take it for a drive or use a battery charger to boost the battery. 

Step two

With the battery reading above 12.5v, it’s now time for step two – The crank test. The crank test stresses the battery, and while stressed, it measures the min voltage.

The crank test is as follows:

  • Remove the fuel pump fuse for testing (if possible)
  • Voltmeter set to 20 v DC
  • Set Min/Max capture
  • Place the red probe on the red positive battery pole and the black probe on the negative battery pole
  • Have helper crank over the engine
  • Check the min reading

A reading below 9v means the battery is indeed faulty and needs to be replaced.

If your battery tested above 9v, then we can move on and look at the next most likely issue – a Faulty alternator.

2 Faulty Alternator

An alternator is, as you know, the source of your battery power. Your battery is used to start your truck, but it’s the alternator’s job to provide all the power once your truck is running; in addition, your alternator must replenish your battery’s depleted power.

An alternator is driven by the engine and drive belt; the belt should be inspected for wear; if the belt isn’t turning the alternator, then it can’t do its job.

Assuming your belt is good, we have a couple of other common alternator issues to check; they are:

  1. Outputting voltage – Is your battery getting the correct voltage
  2. Diode test – Are diodes stealing voltage from your battery

1 Checking Alternator Voltage Output

Your alternator must output the optimum voltage for the given electrical demands of your truck. We can easily test its performance with a voltmeter.

The test is as follows:

  • Engine idling
  • Turn lights, rear heated screen, and heater fan on
  • Set the voltmeter to 20 v DC
  • Red probe on the positive and black on the negative battery post
  • A reading between 13.5 and 15 volts means all is working well here

If you have read outside this, suspect an alternator issue and further diagnose.

2 Checking Alternator Diodes

Your alternator produces a voltage in AC (Alternating Current), meaning it flows back and forth, which isn’t much good when trying to charge a battery. It’s like one step forward and one step back – we never get anywhere. 

That’s where the diode comes in; they allow power to flow to the battery from the alternator but won’t allow it to flow back to the alternator. Great, now we have power flowing to and staying in the battery, just what we want.

You can imagine what happens when a diode fails; the alternator steals your battery’s power, the opposite of what it’s supposed to do.

Luckily we can test the diode; most voltmeters have a diode test function. The test is as follows:

  • Disconnect the battery negative cable
  • Set meter to diode function
  • Place positive meter probe on alternator battery feed
  • Place negative probe on alternator metal casing
  • Note the reading
  • Now reverse the probes and note the reading

If both your battery and alternator tested good, then we can move on and look at the next most likely issue Faulty accessory wiring.

3 Faulty Accessory or Accessory Wiring

Some common causes of self-inflicted battery drains include the following accessories:

  • Trailer socket
  • Trailer wiring issue
  • Light bars
  • Power steps
  • Infotainment systems
  • Trackers
  • Airbags suspension kit
  • Lift kits
  • Remote start kit
  • 12v outlet power accessories

Basically, anything that’s after-market, i.e., not standard equipment, is a likely source of our battery drain.

We’ll get to the business of locating the source of our drain shortly, but first, we’ll look at what tools we’ll need to make this job move like butter.

Tools We’ll Need To Find and Fix Battery Drain 

Locating a battery drain seems like a mammoth task; with hundreds of circuits and miles of cables in your truck, the problem could be anywhere.

That’s all true, but we will use some old-fashioned common sense and some pretty basic tools to hack the crap out of this problem.

To test the battery and find the source of the short, we’ll need some or all of the following:

Voltmeter – The meter checks voltage, amp draw, and resistance. Some fancy ones check temperature and frequency and a ton of other stuff, but we won’t need anything that sophisticated.  We’ll need a basic voltmeter; a cheap $20 meter will work just fine, and I’ve added a link to the meter I recommend for those that don’t have or can’t borrow one.

Power probe – The Power probe isn’t necessary; I’ve listed it because it’s the model I use, and it does make the hunt a ton easier. A power probe is a pro tool and obviously more expensive than a basic voltmeter.

Basic hand tools – We’ll need the usual hand tools that a Silverado owner will already likely have in the truck. We’ll need screwdrivers, wrenches, a socket set, and a screw gun would be great.

Wiring diagrams – Hopefully, we won’t need a wiring diagram, but we may. Don’t sweat this for the moment; when the time comes, I’ll link you to a post I wrote about a beginner’s guide to reading a wiring diagram.

For now, here’s a link to reliable wiring diagrams for your truck supplied by Mitchells 1.

That’s the list of tools needed to locate the problem; now, here is the list of basic tools we’ll likely need to fix the wiring short.

Soldering gun – We’ll need a solder gun to solder wires together. Soldering is the most reliable way to join wiring.

Insulating tape – Tape is used to insulate and protect the wiring from coming loose.

Pliers – Used to strip wiring.

Sleeves – Used to protect wiring from weather ingress.

Dielectric grease – Helps promote connectivity and eliminate fretting and corrosion.

That’s it! We are now tooled up for the job. But just before we go deep, it is helpful to have a basic understanding of what exactly we’re hunting for. And so, in the next section, we’ll cover what the hell a short actually is.

What is a Short?

Battery power moves around in a circuit; it leaves the positive side of your battery and strives to find the shortest possible route back to the battery, but on the negative side.

By routing this energy through a motor or a light (we call it the load), we can harness its available energy. A short, then, is where the potential energy bypasses the load, meaning it takes a shortcut – known as a short.

Short Hunting

In this section, we’ll begin the hunt. I’ll keep the process as simple as possible. I won’t use fluffy words. 

Short finding is a two-step process:

1 Locate the affected circuit

2 Pinpoint the short within the affected circuit

As the wiring landscape in your truck is large, systematically going through each wiring circuit just isn’t practical, so it makes sense to narrow down the field a little.

A short circuit usually blows the fuse, which is great for a couple of reasons – first, the drain on the battery ceases, but also, the circuit is identified by the blown fuse. The process is largely common sense.

That said, what if the fuse doesn’t blow, meaning the drain isn’t large enough to blow the fuse but large enough to drain the battery after a few days?

For this type of drain, we have a hack known as the “Volt drop test,” and we’ll get to that a little later. But first, we’ll try to narrow the landscape a little by eliminating the second most likely cause of our short – “Accessory drain,” and that’s what we’ll do next.

Accessory Eliminating Round

Eliminating our truck accessories is easy, and it makes sense to do it now before we invest time in circuit checking, especially given accessories’ reputation for wiring issues.

If you have electrical accessories on your Silverado, now’s the time to eliminate them as a possible source of a short by removing their power source.

The easiest way to disconnect an accessory from the power source is by removing its fuse. That said, some accessories may be piggybacking on another circuit or, worse, may not be fused at all.

In those cases, we’ll need to disconnect the accessory power wire altogether, which will be a little more work.

The process of removing accessory power and getting feedback may take a few days, but it is worth it.

If you find your drain disappears, you found your problem. Run a visual and look for damaged wiring. 

If you have more than one accessory, it may not be obvious which is to blame. An accessory that doesn’t work or has been acting up is a great place to start if no such clues are available, power up each accessory in turn, and retest.

In general, it is more likely to be shorted accessory wiring than a failed accessory itself.

If the accessory elimination hasn’t helped any, then this next one will. We’ll need to break out the voltmeter again; in the next section, we’ll run a really simple test known as the Volt drop test in Step 1 below. 

Step 1 Identify the Circuit

The mission of step 1 is to identify the affected circuit, and to do that; we use a simple test known as the Volt drop test. We’ll need a voltmeter to run this test, but it is simple and easy to interpret.

Before running the volt drop test, we’ll need to prepare your truck. Your truck uses a ton of computers, as you know to manage systems, and these computers all use some power when in use. After about 45 minutes of inactivity, these modules go asleep and stop using power. 

To run the volt drop test successfully, we’ll need your truck to be in sleep mode and to do that; we’ll need to take the following steps:

  • Open doors
  • Trip door latches
  • Open hood
  • Trip hood latch
  • Remove fuse box covers
  • Remove keys
  • Wait 45 minutes for modules to go asleep

We are now ready to run the volt drop test and identify the affected circuit.

The volt drop test is as follows:

  • Set the meter to Millivolts (Mv)
  • Place a probe on either side of each fuse in turn
  • Finding a fuse that reads above 0v indicates the affected circuit

Using your driver’s handbook, identify the circuit by the fuse number. That’s the circuit we’ll need to focus on, and now it’s – Step two – Pinpoint the short

I told you it was easy!

Step 2 Pinpoint the Short

To pinpoint a short we’ll ideally need to know where the circuit goes around the truck. Blindly stripping panels to access wiring isn’t a good use of your time. And so we’ll need access to a wiring diagram. I recommend you use Mitchells 1.

As we’ll be measuring circuit resistance in the following tests, the circuit must be dead, and so to prepare for the tests, go ahead and –

  • Remove the battery-negative terminal
  • Remove the load (unplug the light, motor, etc., whatever the circuit is driving)

The pinpointing process is simple, and here it is:

To pinpoint the location of the short, we’ll need to open the circuit at a convenient location (usually a block connector). That effectively breaks the circuit in two, allowing us to identify which half of the circuit has the short.

Pretty easy so far, right? Great!

Now we’ll need our voltmeter set to resistance to check which half of the circuit offers little resistance to ground; that’s the half with the problem. 

This test can be repeated by further breaking the circuit in half and testing and so on until you visually find the damaged section.

And now it’s a matter of fixing the wire, and that’s what we’ll do next.

Fixing a Short

Most wiring shorts are caused by a rubbed wire, meaning the wire insulation rubs through and creates a short by grounding on the chassis.

The best fix is to cut the rubbed section of wire out of the circuit and re-join it if there’s sufficient length; if not, we’ll need to add a section of wire.

Either way, we’ll need to ensure the wire join is secure and won’t cause trouble in the future. The best repair is soldering, and the whole process is as follows:

  • Heat the soldering gun now (if electrically operated)
  • Strip wiring ends by about 3/4 inch
  • If adding a section of wire, be sure it’s the same gauge wire
  • Add a heat shrink sleeve
  • Twist the wire around each other
  • Thin the soldering tip (cover with solder)
  • Heat the wiring and add solder
  • When cool, slide heat shrink and heat with a heat gun to shrink
  • Add black insulation tape to secure the wire to the wiring loom

Sum Up

A faulty battery or alternator, followed by poor accessory wiring, are the most common causes of a battery drain. These should be eliminated as possible causes of a battery drain before moving on to short circuit diagnosis.

Short finding is a two-step process; the first step is – Identify the circuit at fault, and the second step is – Pinpoint the short within the circuit.

The fix usually involves repairing a rubbed-through wire by removing the damaged section and soldering in a new section with weatherproof heat shrink insulation.


John is a technical writer here at He's a Red seal qualified mechanic with over 25 years experience working on all types of Pickups. He's skint his knuckles on them all, including Ford, GM, RAM, Toyota, and Land Rover.

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