Basic Symptom Diagnosis flashcards

No-crank: the engine does not turn over, so check the starting circuit (battery, cables, interlocks, solenoid, starter). Crank-no-start: it cranks at normal speed but never runs, so check fuel, spark, air and engine control.

No. Lamps draw a few amps; a starter draws well over 100 A. A weak battery or corroded cable can light bulbs brightly yet collapse under starter load. Test battery voltage and connections.

$V_{\text{terminal}}=V_{\text{rest}}-I{R}_{\text{internal}}$. With 12.6 V, 150 A and 0.02 $\Omega$: drop is 3 V, so the terminals read about 9.6 V during cranking.

$V_{\text{drop}}=IR$ and $P=I^{2}R$. At 150 A through 0.004 $\Omega$: 0.6 V lost before the starter and 90 W of heat, which is why a bad terminal can feel hot.

Steady MIL: the computer saw a fault affecting emissions or engine control; have it checked soon. Flashing: severe misfire that can damage the catalytic converter. A DTC points to a circuit or area, not a specific failed part.

No. Clearing erases freeze-frame data and resets readiness monitors to incomplete, but the cause remains and the lamp may return. Record freeze-frame data before clearing; a permanent code clears only after the computer verifies the repair.

A misfire follows engine rpm and can be felt while parked or idling. A wheel or tire shake follows road speed, often in one speed band like 60 to 70 mph, and disappears when stopped.

$d\propto v^2$, and $d=\frac{v^2}{2a}$. Doubling speed from 30 to 60 mph makes braking distance 4 times longer: 45 ft becomes about 180 ft. Reaction distance adds $d=vt$ on top.