Bay method
CAN 60 Ω & parasitic mV helper
High-speed CAN with two 120 Ω terminators reads about 60 Ω key-off. Parasitic draw from voltage drop across a fuse uses typical published blade-fuse resistances — the Power Probe / ALLDATA method techs already print as a PDF.
CAN-H to CAN-L resistance
Two terminators (typical healthy bus)
Two 120 Ω terminators in parallel read about 60 Ω. That is the expected key-off resistance on high-speed CAN.
If scan tools still cannot talk, move to voltage (key on: ~2.5 V bias, ~1.5–3.5 V swing) — resistance is only the first check.
Parasitic draw from mV across a fuse
Estimated draw
51.9 mA
0.052 A · typical sleep budget 50 mA
Vs sleep budget
Over
Above the common 50 mA sleep budget used in many parasitic-draw write-ups. Confirm the vehicle is asleep, then isolate this circuit.
Fuse resistance values are typical published blade figures (the Power Probe / ALLDATA style chart). A 0.5 mV drop on a 10 A fuse is about 65 mA — over a 50 mA budget. Measure the real fuse if the number matters in court.
Theory
Resistance first, then voltage, then isolate
High-speed CAN should read about 60 Ω key-off. 120 Ω is one terminator. Near 0 Ω is a short. Open is a broken pair or the wrong pins. Parasitic draw from millivolts across a blade fuse is I = V/R using typical published fuse resistances — a 0.5 mV drop on a 10 A fuse is about 65 mA, over a common 50 mA sleep budget. Modules can stay awake twenty minutes after key-off. This is not a pin-out database.
0.5 mV ÷ 7.7 mΩ (typical 10 A blade) ≈ 0.065 A = 65 mA.
How to use it
- Role
- Technician / auto electrician (P03)
- Shop-day step
- DVI / diagnosis on a no-comm or flat-battery RO
- Do
- Confirm sleep, measure, then isolate the circuit. Write the ohms or mA on the job card.
- Do not
- Do not replace a module from a 60 Ω reading, and do not pull fuses on a car that is still awake.
Official sources
Related tools
Method helper, not a wiring diagram and not a diagnosis. Fuse resistance varies by brand.