09/07/2026 10:54 am
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Automotive Q&A
What should an intermittent-fault test plan contain before parts are swapped?
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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A vehicle with an occasional stall arrived with no current code and normal bay data. The first instinct was to swap a crank sensor because it is common. We want a written plan that survives several road tests and technician handoffs.
Which hypotheses and triggers should be listed?
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10/07/2026 9:19 am
Define the symptom precisely, known enable conditions, evidence already collected and the systems that could remove torque or engine speed. Rank hypotheses and assign each a discriminating measurement: crank signal, power relay output, fuel pressure, network state and ignition command on the same time base. State how the fault will be induced safely and what result supports or rejects each branch.
Preserve failed and normal captures. An intermittent plan should narrow the next test after every run rather than restarting from a parts list.
Topic starter
11/07/2026 9:21 am
The plan captured ECM power and crank signal together. On the third road test, ECM power fell 200 ms before RPM data vanished, rejecting the crank-sensor guess. The relay feed terminal was repaired and the normal capture became the verification baseline.