Truck Center
Driver Knowledge Base
Ask it the way you'd ask another driver: “why won't my truck complete a regen”, “what is a derate”, “is this load worth it”.
18 answers
Search by question, symptom or part.
Aftertreatment
Why won't my truck complete a regen?
A regen needs heat, fuel, air and a healthy sensor picture. If any one of those is missing the ECM aborts and soot keeps stacking until you get a derate.
Aftertreatment
DEF quality and SCR faults explained
Most 'bad DEF' codes are not bad fluid — they are a NOx sensor, a dosing problem or an exhaust leak that makes the math look wrong to the ECM.
Aftertreatment
What is an engine derate and how do I clear it?
A derate is the ECM protecting the engine or forcing an emissions repair. There are two kinds and they clear very differently.
Diesel Engines
How to read SPN and FMI fault codes
SPN tells you what circuit or component the ECM is unhappy about. FMI tells you how it is unhappy. Together they point you at a wiring test, not a parts order.
Diesel Engines
Diesel hard start and no-start diagnosis
Every diesel no-start comes down to fuel, air, compression or a signal the ECM needs. Prove which one is missing before you touch a part.
Diesel Engines
Loss of power and boost — turbo and VGT checks
Low power with no codes is usually a leak or a restriction. Low power with a VGT code is usually soot-stuck vanes or an actuator that cannot move them.
Diesel Engines
Overheating on a hill — what to check
Heavy trucks overheat because of airflow, coolant flow or a fan that is not commanded on. Work outside-in — the cheap checks are all on the outside.
Electrical
No crank, dead batteries and charging problems
Most 'bad starter' calls are a voltage drop through a cable or ground. Ten minutes with a meter tells you which side the problem is on.
Electrical
How to chase an intermittent electrical fault
Intermittents are found with live data and a wiggle test, not with parts. Make the fault happen while you are watching it.
Air & Brakes
Air system leaks and pressure loss
A truck that will not build or hold air has a leak, a tired compressor, or a dryer purging when it should not.
Air & Brakes
Brake adjustment and out-of-service limits
Automatic slack adjusters still need to be checked. Excess pushrod travel is one of the fastest ways to get placed out of service.
Drivetrain
Clutch and transmission symptoms decoded
Slipping, dragging and hard shifting each point at a different part of the system. Name the symptom precisely and the diagnosis is short.
Maintenance
Building a PM schedule that actually gets followed
Preventive maintenance only works if it is written down and tied to a number you already track — miles or engine hours.
Maintenance
A pre-trip inspection that passes every time
Inspectors look at the same short list over and over. Cover that list the same way every morning and roadside stops get boring.
Owner-Operator
Cost per mile explained for owner-operators
You cannot judge a load without knowing your own number. Cost per mile is fixed costs plus variable costs divided by the miles you actually run.
Owner-Operator
Is this load worth it? Judging a rate in 60 seconds
Take total pay, subtract fuel and the deadhead to get there, then compare what is left against your cost per mile for the whole trip.
Owner-Operator
Hours of service in plain English
Three clocks run at once: driving time, the daily window, and the weekly cycle. Break any one and the truck stops.
Owner-Operator
Buying your first truck without getting burned
Inspect the truck like it is already yours, and price the repairs you find into the offer instead of hoping they never happen.
Still stuck?
Ask a Tech takes your truck, codes and symptoms and gives you a ranked diagnostic path before you spend money on parts.