START WITH EVIDENCE
Diagnose a Fault
Move from a symptom, trouble code, system, or component to a focused test plan.
BROWSE THE DIRECTORY
Choose a starting point
By Symptom
Start with what the driver can see, hear, feel, or smell, then narrow the cause with evidence.
8 guides 02By Trouble Code
Understand what a diagnostic trouble code monitors, what it does not prove, and which tests come next.
10 guides 03By System
Follow system-level diagnostic paths for powertrain, electrical, chassis, HVAC, network, and EV concerns.
10 guides 04By Component
Test sensors, actuators, wiring, and mechanical parts before authorizing replacement.
9 guidesRECENTLY ADDED
From this section
Rough Idle After Warm-Up: A Diagnostic Path
A warm-engine rough idle is a condition to measure, not a reason to order an idle valve, injector, or ignition coil.
Read guideCranks but Will Not Start: The First Five Checks
A no-start diagnosis moves quickly when cranking speed, module communication, spark or ignition command, injector command, and mechanical timing are checked in order.
Read guide
Intermittent Stall: What to Log Before Restarting
The few seconds around an intermittent stall contain more evidence than a normal-running inspection after the engine restarts.
Read guide
Engine Overheats in Traffic but Not on the Highway
An overheat that appears at low road speed often points toward airflow or fan-control evidence, but coolant level, circulation, pressure, and sensor accuracy still need confirmation.
Read guide
Brake Pedal Pulsation: Speed-Based Checks Before Parts
Pedal pulsation can reflect disc thickness variation, hub runout, wheel-speed control activity, or looseness; the road-speed pattern helps separate them.
Read guideBattery Drains Overnight: A Parasitic-Draw Test Plan
An overnight discharge requires separate proof of battery capacity, charging performance, and key-off current after the vehicle has entered sleep mode.
Read guide