What's Your Car Doing?
Pick your symptom to find the likely codes, causes, and fixes.
Check Engine Light Flashing
Flashing CEL usually means a misfire -- stop driving and diagnose immediately.
Learn more →Car Shaking at Idle
Vibrations at idle often point to misfires, vacuum leaks, or worn motor mounts.
Learn more →Car Won't Start
No-start conditions caused by battery, starter, fuel, or immobilizer issues.
Learn more →Engine Overheating
Rising temp gauge or steam from the hood -- coolant, thermostat, or fan problems.
Learn more →Car Won't Accelerate
Loss of power under throttle from clogged filters, bad sensors, or transmission faults.
Learn more →Rough Idle
Engine surges or stumbles at idle -- dirty IAC, vacuum leaks, or fouled spark plugs.
Learn more →Poor Gas Mileage
Sudden drop in fuel economy from O2 sensors, injectors, or air filter issues.
Learn more →White Smoke from Exhaust
White exhaust smoke usually means coolant is burning -- possible head gasket leak.
Learn more →Engine Knocking Noise
Knocking or pinging under load from bad fuel, carbon buildup, or bearing wear.
Learn more →Car Jerking When Accelerating
Jerky acceleration from dirty injectors, failing ignition coils, or transmission slip.
Learn more →Battery Light On
Battery warning light indicates charging system failure -- alternator, belt, or wiring.
Learn more →Car Stalling
Engine stalls at idle or while driving -- fuel pump, sensor, or airflow problems.
Learn more →Gas Smell from Car
Fuel odor inside or outside the car from EVAP leaks, injector seals, or fuel lines.
Learn more →Car Losing Power
Gradual or sudden power loss from exhaust restrictions, boost leaks, or fuel delivery.
Learn more →Diesel Truck Symptoms
Heavy-duty and light-duty diesel-specific issues -- DPF, DEF, EGR, turbo, and cold start.
DPF Light On
Diesel particulate filter warning -- know whether to stop or keep driving to regen.
Learn more →Forced Regen Needed
When passive regen fails, the DPF needs a forced regen -- what it is and when to do it.
Learn more →DEF Quality Fault
Bad DEF, contamination, or sensor faults causing derate or countdown warnings.
Learn more →CP4 Pump Failure Signs
Catastrophic CP4 fuel pump failure on 6.7 Power Stroke and LML Duramax -- warning signs.
Learn more →EGR Cooler Failure
White smoke, coolant loss, or overheating from a cracked EGR cooler -- common diesel failure.
Learn more →Blue Smoke / Oil Burning
Blue exhaust smoke means oil is burning -- turbo seals, valve guides, or piston rings.
Learn more →Turbo Stuck / Underboost
Sticking VGT vanes causing low boost, low power, or black smoke -- calibration often helps.
Learn more →Hard Cold Start (Diesel)
Long cranking in cold weather -- glow plugs, block heater, fuel gelling, or battery issues.
Learn more →Still not sure?
If you already have a code, search by code on the homepage. Or browse all codes by category to narrow it down.