Customer's 2018 Silverado kills a brand-new battery in about four days sitting.

Parasitic draw test procedure:

1. Disconnect negative battery cable. Set your multimeter to amps (10A range), connect in series between the negative cable and battery post.

1. Wait 10-20 minutes for modules to go to sleep. Some GM vehicles need up to 30 minutes.

1. Read the draw. Normal parasitic draw for a 2018 Silverado should be under 50mA (0.050A). GM spec is typically 40-50mA max.

1. If over limit: Pull fuses one at a time until the draw drops. That circuit is your culprit.

Common offenders on these trucks:

• Aftermarket electronics (dash cams, trailer brake controllers)
• Faulty ignition switch
• BCM or radio staying awake
• Aftermarket alarm/remote start

Important: Make sure doors are closed, key is out, and wait for the security light to go out before testing. Some modules (like the radio) may take several minutes to sleep.

If you're reading over 50mA, start pulling fuses. The number you're looking for is under 50mA — anything higher indicates a draw that will kill your battery.

Safety note: Don't exceed your meter's 10A limit or you'll blow the fuse. If you suspect a huge draw, use a test light first to avoid damaging your meter.

Test Procedure (GM-specific):

1. Prep: Close all doors, hood, tailgate. Remove key fob >20 ft away. Disable OnStar (pull fuse F39 in rear fuse block or disconnect module). Wait 20–45 minutes for all modules to enter sleep mode (critical on GMT1XX platform).
2. Connection: Use a low-amp inductive clamp (Fluke i30s/i410) on the negative battery cable. Do not break the circuit with a DMM in series—waking modules resets the timer.
3. Read: Observe clamp meter after sleep timeout.

Target Spec: ≤ 30 mA (0.030 A) per GM Bulletin #PIP5589E.

• 30–50 mA: Marginal (investigate).
• > 50 mA: Excessive draw.

Common 2018 Silverado Culprits:

• Body Control Module (BCM) failing to sleep (Software update PIP5589E / TSB 18-NA-171).
• Trailer Brake Control Module (internal short).
• Infotainment/Head Unit (stay awake via USB/Bluetooth).
• Aftermarket accessories (remote start, amps, GPS trackers).

Isolation: Pull fuses one at a time (refer to owner’s manual fuse chart) while watching clamp. Note which circuit drops draw to spec. Check underhood (ECM, ABS, cooling fan) and rear (BCM, trailer, liftgate) blocks.

Pro Tip: If draw is ~85–150 mA steady, suspect a module stuck awake. Disconnect BCM C1/C2 connectors; if draw drops, update BCM software via SPS/GDS2 before condemning hardware.

Safety: Wear glasses. No smoking. If draw > 1 A, check for stuck relay (cooling fan, fuel pump) immediately.