Truck Won't Crank After Two Nights - Chasing a Parasitic Draw

Arithmetic first. 0.085 A × 48 h = 4.1 Ah, which is roughly 6% of a 70 Ah battery. A healthy, fully charged battery can absorb that and still crank. So the number you are looking at does not explain the symptom - chasing it to zero would be a wasted afternoon.

What that means for the diagnosis:

• The draw is probably intermittent or higher at times you are not watching - a module that wakes on a timer, a phone paired to the head unit, a keyless-entry antenna polling, or the aftermarket remote starter's own sleep logic.
• 85 mA is still above the usual 20–50 mA guideline, so it is a real finding, just not the whole story.
• Battery condition is not fully proven. A conductance test grades cold-cranking ability, not reserve capacity. A battery that passes CCA can still have lost capacity.
• Verify the measurement itself - clamp zero drift, a door ajar switch, or a hood switch that woke the BCM will all inflate the reading.

Next step is not fuse-pulling; it is a logged measurement over 12–24 hours so you catch the wake events.

Why fuse-pulling is a trap here: pulling a fuse interrupts module keep-alive memory and can wake the whole network, resetting the 20–60 minute sleep timers. You end up chasing a moving target and may never see the original state again.

Better sequence:

1. Set up a data-logging meter or low-amp clamp in series/around the negative cable and record for several hours, including overnight. Note the time and magnitude of any step changes.
2. Once you know the size and timing of the wake event, use the millivolt drop across fuses method - measure in millivolts with a high-resolution meter and convert using the fuse's rated resistance (or the manufacturer's chart, since the conversion is different for mini, ATO and maxi fuses). This works with everything still connected and asleep.
3. Confirm on the suspect circuit with a low-range clamp around that individual feed rather than trusting the mV conversion alone.
4. Use a non-contact thermometer or amp clamp on the alternator as a quick check for a leaking diode, and disconnect the aftermarket remote starter's constant feed temporarily to see whether the 85 mA disappears.
5. Check for a TSB or module reprogramming once the module is identified - a known wake-up complaint is often fixed by software, not parts.

Disconnecting it removes the customer's feature, so treat that as a diagnostic step, not a repair.

Before you cut anything:

• Confirm the unit is actually faulty rather than mis-wired. Aftermarket modules are frequently tapped to a constant 12 V source instead of an ignition-switched or retained-accessory feed, so they never sleep. Re-terminating to the correct source often fixes the draw with the feature intact.
• Check the manufacturer's sleep-current specification for that unit and compare against your measured value.
• Verify the installer did not use Scotch-Lok connectors or a fuse-piggyback that has damaged the OEM harness; document anything you find, because you are now responsible for that circuit.

Repair: correct the supply source, add a properly rated fuse at the tap point, and re-measure key-off current after the full sleep cycle to prove the repair. Record before/after values on the RO.

Customer conversation: explain that the accessory is the source, that the vehicle's own systems are within spec, and get authorization before modifying a third-party installation - including telling them that if the unit itself is defective, the accessory vendor is the right warranty path.