#cold start
11 posts in Car Diagnostics blog about "cold start" — OBD-II diagnostics, DTC codes, repair. ← All posts
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Long crank on the first start: pressure that leaked away overnight
Three seconds of cranking on the first start and instant restarts all day. That pattern points at fuel pressure, and there is a two-minute test for it.
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P0316: misfire detected on startup — the cold-start-only fault
P0316 only counts misfires in the first seconds after cranking. That narrow window points at a specific short list of causes that a warm-engine test will never reproduce.
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P0411 to P0414: secondary air injection flow and valve circuit
The system only runs for a minute after a cold start, which is why the fault is nearly invisible and the code arrives with no symptom at all.
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P0421 and P0422: warm-up catalyst efficiency below threshold
A separate code for the close-coupled catalyst, and a separate meaning: this one is usually about how the engine behaves in the first minute, not about the converter.
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Rough when cold, fine when warm: why that happens
A symptom that disappears as the engine warms is a clue, not a triviality. Why a cold start exposes what a warm engine hides.
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Will not start in the cold: five causes in the order you should check them
Frost does not create new faults — it finishes off the ones already marginal. Diagnosis by symptom: does not crank, cranks without catching, catches then stalls. Each leads somewhere different.
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Do you need to warm the engine up? What live data says instead of opinions
The warm-up argument has run for decades on conviction alone. But the control module shows exactly what happens on a cold engine — and that settles most of both sides' arguments.
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P0113 and P0118: temperature sensors — cheap parts that cost you fuel
A sensor costing a few dollars can raise consumption by a third, ruin starting, and break the cooling fan. The two most important temperature sensors, and why their failures are so easy to miss.
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Secondary air injection P0410: runs 90 seconds a day and fails anyway
A pump that only runs on a cold start, and only for a minute and a half. It sits idle the rest of the time — which is precisely why it corrodes, seizes, and eventually produces a code that fails your emissions test.
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Diesel glow plugs: codes P0670-P0674 and why "cold start" stops working
What glow plugs are, how OBD-II sees their state via P0670, P0671-P0678, why one dead plug ruins the whole cold start, and how much replacement costs on a 4-cyl diesel.
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Winter Check Engine: 7 typical codes that only appear in the cold
Why Check Engine turns on in winter and disappears in summer: P0128 (thermostat), P0300 (cold-start misfire), P0442 (EVAP), P0507 (idle), P0116 and what to do with "seasonal" codes.