Parasitic draw, voltage drop and A6 diagnosis

Incorrect: Technician A is wrong to replace the module now; its ground and bus wiring are untested, and a lost ground mimics a dead module.

Correct: Technician B is right: a module with power but no ground cannot run or talk on the bus, so the ground is tested under load first.

Incorrect: Both cannot be right, because Technician A's replacement skips the ground check Technician B calls for.

Incorrect: Choosing neither ignores that Technician B's ground check is the correct next step.

Incorrect: With the ABS module unplugged the reading stays at 2.3 Ω, so the short is elsewhere.

Incorrect: The ECU is not in the table, and the BCM result already accounts for the short.

Incorrect: The HVAC module is not in the table; the BCM result already explains the fault.

Incorrect: Unplugging the transmission controller moves the reading only 0.1 Ω, so the short remains.

Correct: Unplugging the BCM raises the reading from 2.3 Ω to a normal 60 Ω, so the short is in the BCM or its connector.

Incorrect: Surface charge affects voltage readings, not the current the vehicle's loads pull through the ammeter.

Incorrect: A short draws steadily; it would not fade on its own over several minutes.

Incorrect: A meter fuse is either intact or open; it cannot produce a reading that tapers.

Incorrect: A leaking diode gives a steady draw, not a high reading that tapers off.

Correct: Connecting the ammeter restores power, the modules wake and draw amps, then the draw falls as they sleep again.

Incorrect: An ammeter measures current; it cannot read the resistance of the ground path.

Correct: Isolating the load removes the parallel paths through the other loads, so the meter reads only this ground path.

Incorrect: An ohmmeter across a battery gives no useful reading and can damage the meter.

Incorrect: A jumper bypasses the very splice under test, so a bad ground would read good.

Incorrect: An ohmmeter needs a dead circuit; live voltage corrupts the reading.

Incorrect: 40 Ω means three terminators in parallel, which takes an extra resistor, not a missing one.

Incorrect: 60 Ω is the normal reading with both terminators present.

Incorrect: An infinite reading needs both terminators or the backbone open, and one resistor is still in place.

Incorrect: 240 Ω would mean two terminators in series, but on the bus they sit in parallel.

Correct: With one 120 Ω terminator missing, the meter reads only the remaining resistor, 120 Ω.

Incorrect: CAN_L reads a normal 2.5 V, so it is not shorted to ground.

Incorrect: A ground short pulls CAN_H to about 0 V, not 12 V.

Incorrect: Shorted lines would read the same voltage, and here they differ by 9.5 V.

Correct: CAN_H at 12 V instead of its normal 2.5–3.5 V means it is shorted to a battery feed.

Incorrect: CAN_L is at its normal 2.5 V; the line at battery voltage is CAN_H.

Incorrect: Pulling one fuse at a time is how the circuit is found, and these readings are enough.

Incorrect: Removing fuse #2 brings the draw back to normal, so that circuit is clearly involved.

Incorrect: Fuse #1 removes only 20 mA, a small normal keep-alive load.

Incorrect: Fuse #1 accounts for 20 mA against 250 mA for fuse #2, so they are far from equal.

Correct: Pulling fuse #2 removes 250 mA and leaves a normal 50 mA, so that circuit carries the excess draw.

Incorrect: A ground-side open stops current, but the fuse output would still read source voltage.

Incorrect: The switch is downstream and cannot remove voltage from the fuse output terminal.

Correct: Voltage enters the fuse but does not come out, so the fuse element itself is open.

Incorrect: With the load disconnected no current flows, so a resistive holder would still show 12 V on both sides.

Incorrect: An open past the fuse still leaves 12 V at the fuse output terminal.

Incorrect: A draw within specification says nothing against the battery.

Incorrect: A rule-of-thumb 50 mA figure does not override the manufacturer's 70 mA limit for this equipment.

Incorrect: Disabling the module is unnecessary; the 70 mA allowance already includes it.

Incorrect: The 35 mA figure applies to a vehicle without telematics; this one has its own 70 mA limit.

Correct: This vehicle's own limit is 70 mA because of the telematics module, and 60 mA is below it.

Incorrect: The solenoid is not on the alternator's B+ cable, so disconnecting that cable would not stop it.

Correct: The draw vanishes when the alternator B+ cable is disconnected, so current is leaking back through a shorted rectifier diode.

Incorrect: A lamp on its own circuit would keep drawing after the alternator cable was disconnected.

Incorrect: Internal self-discharge never passes through the ammeter, so it cannot show up as 2 A of draw.

Incorrect: A healthy alternator draws almost nothing with the engine off; 2 A is a fault.

Incorrect: An open coil would keep voltage off pin 85; 12.5 V there proves the coil conducts.

Incorrect: The contacts never get a chance to close, because the coil is not being grounded.

Correct: Pin 85 reads 12.5 V when commanded, so the coil conducts but the PCM side is not completing the ground.

Incorrect: Pins 30 and 86 both show a full 12.5 V, so the feeds are fine.

Incorrect: An open pump wire would still show voltage at pin 87 once the relay closed; it reads 0 V because the relay never energized.

Incorrect: 2.00 A counts the blower branch and leaves out the relay coil.

Incorrect: 0.15 A is the relay coil alone; the blower branch is missing.

Correct: The motor plus resistor 1 is 6 Ω for 2 A, and the 80 Ω relay coil adds 0.15 A in parallel, so 2.15 A.

Incorrect: 12.15 A treats the blower branch as 1 Ω, but the motor and resistor 1 add up to 6 Ω.

Incorrect: 6.15 A uses the 2 Ω motor alone and ignores resistor 1 in series with it.

Incorrect: Here pulling any fuse wakes the modules and clears the draw, so the fault vanishes each time.

Incorrect: Hourly voltage readings confirm a drain but cannot name the module causing it.

Incorrect: A new battery still feeds the module that stays awake, so the draw returns.

Incorrect: Disconnecting the battery resets every module, so the draw is gone before it can be traced.

Correct: The scan tool shows which module stays awake while the draw is present, without disturbing any circuit.

Incorrect: One missing terminator distorts signals but leaves the two lines at different voltages while traffic runs.

Incorrect: An open CAN_H would float or sit at a different voltage from CAN_L, not match it exactly.

Incorrect: A dead scan tool does not change the bus voltages a DMM measures.

Incorrect: An open CAN_L does not force both lines to the same 2.5 V.

Correct: Both lines at the same 2.5 V with zero differential means they are tied together and cannot carry data.

Incorrect: An ammeter does not display volts; across a battery it becomes a short circuit.

Incorrect: No reading across the posts is normal, and draw is never measured in parallel.

Correct: An ammeter has almost no resistance, so across the posts it shorts the battery and blows its fuse; draw is read in series with a cable.

Incorrect: The fuse does blow, but a parallel hookup is the mistake itself.

Incorrect: Across the posts the ammeter carries a very large current; it does not read zero.

Correct: 2.0 mV ÷ 20 mΩ = 100 mA, the only circuit above the 50 mA threshold.

Incorrect: 0.8 mV ÷ 16 mΩ = 50 mA, at the threshold rather than over it.

Incorrect: 0.2 mV ÷ 5 mΩ = 40 mA, below the threshold.

Incorrect: 0.5 mV ÷ 10 mΩ = 50 mA, equal to the threshold but not above it.

Incorrect: 1.0 mV ÷ 25 mΩ = 40 mA, below the threshold.

Correct: Technician A is right: wiggling the harness while watching pump voltage recreates an intermittent open, and the relay already tested good.

Incorrect: Technician B would replace a relay that already tested good, which does not find the intermittent loss.

Incorrect: Only Technician A is right; swapping a relay that tested good is not a diagnosis.

Incorrect: Technician A's wiggle test is the correct way to catch an intermittent wiring fault.