A6 ELECTRICAL // FLAGSHIP DIAGNOSTIC
2022 CHEVROLET SILVERADO 1500 LT
5.3L V8 · Intermittent network fault
Customer concern
"Truck stalls intermittently. Dash lights flicker. Sometimes won't start. Comes and goes — happened 3 times in the last week."
Initial scan data
DTC: U0073 — CONTROL MODULE COMMUNICATION BUS A OFF DTC: U0140 — LOST COMMUNICATION WITH BCM BATTERY: 12.6V rest / 14.2V running — OK ALTERNATOR: Output normal — OK RIPPLE: <50mV — OK
You've ruled out the obvious. The fault is on the CAN bus. Diagnose the short.
Step 1 · Read the bus
With the key OFF, where do you measure the CAN bus terminating resistance? Click the correct test point on the schematic.
Step 2 · Measure resistance
Probes are on OBD-II pins 6 (CAN-H) and 14 (CAN-L), key off. Read the meter, then interpret it.
FixedIntel DMM · Ω
Expected (healthy bus): two 120Ω terminators in parallel = 60Ω
A reading meaningfully off 60Ω is a real signal, not noise.
Reading: 65Ω. What does it tell you?
Step 3 · Scope the bus
CAN-H to CAN-L, 5ms/div. Capture live traffic and watch for the intermittent.
The marked event — what happened?
Step 4 · Isolate the node
Unplug modules one at a time and re-check resistance at the OBD-II port. When the bus reads ~60Ω, you've found the node with the short. Avoid the terminator-end modules (ECM, BCM) — unplugging those just removes a terminator.
Bus resistance · OBD-II
All modules connected.
Step 5 · Root cause
The short is in the HVAC head unit branch. Here's the harness routing through the dash bracket. What's the root cause?
Diagnosis Closed.
Chafed CAN-H wire at the HVAC harness — repaired with no parts replaced.
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Time elapsed
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Score
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Efficiency
A6 · CAN BUS
Profile +12 pts
Real-shop equivalent
In a real bay, this diagnostic saves ~2.5 hours over the parts-cannon approach. A tech who's 17% faster on electrical recovers ~340 billable hours a year — that's the productivity raise. Every scenario you train sharpens the cert and the daily diagnostic edge.