🔧 Roadside Breakdown Triage

Something has gone wrong at the worst possible place. Pick the symptom and this walks you through what is safe to check, what each finding most likely means, whether you can carry on or stop, and exactly what to say to the shop and dispatch. No guessing in a lay-by at 3 a.m.

Where this comes from, and the limits of a phone at the roadside

The symptom lists are built from the roadside checks a driver can do without tools or a pit: what the gauges and lamps say, what you can hear, what you can see, what is warm and what is not. The air brake thresholds (warning before 60 psi, spring brakes applying between 45 and 20 psi, leakage limits of 2–3 psi a minute released and 3–4 psi applied) and the US warning-device distances come from the CDL manual and 49 CFR 393.95; the DEF derate behaviour varies by manufacturer and is described generally.

The honest limits: a driver cannot diagnose a failed injector, an EGR cooler or a wiring chafe from the shoulder of a road, and should not try to. What this page is good at is telling you which failures are a phone call and which are a do not move this truck, and how to describe the problem so the shop sends the right help the first time.

Never work under a vehicle that is not chocked and secured, never open a hot cooling system, never bleed a hot tyre, and stay off the traffic side of the truck. If the situation is dangerous, the only correct answer is to get yourself out of it and call for help.