OBD-II diagnostic reference
OBD-II codes: start with what you need right now.
20 codes, one page each. Every page leads with the same three answers: can you keep driving, how long you have, and what the repair costs. Read the top of the page and stop. That is usually the whole answer.
- 1
The car is in the driveway. Can I drive it?
Go straight to the codes that park the car. 5 of the 20 mean stop driving now. Open the code index - 2
I want to know what this is going to cost.
Shop ranges for all 20 codes, plus the three things that move the bill: the part, the labor, and where you live. Open the cost guides - 3
I have a symptom and no code.
Shakes at idle, cranks but will not start, smells like raw gas. Find the symptom first, then the code behind it. Open the symptom index
All 20 codes, grouped by what happens if you ignore them
The grouping is the answer most people need. Start at the top.
Stop driving. Park it and read the page first.
5 codesA misfire dumping raw fuel, a timing fault, a dead crank sensor, a computer that stopped talking. Park it until you know which one you have. None of these get better by driving.
- P0016 Do not drive Crankshaft / Camshaft Position Correlation (Bank 1) Shop $300–$1,500
- U0100 Do not drive Lost Communication With ECM/PCM Shop $100–$1,500
- P0300 ≈2 weeks Random or Multiple Cylinder Misfire Detected Shop $120–$900
- P0301 ≈2 weeks Cylinder 1 Misfire Detected Shop $120–$700
- P0335 ≈2 weeks Crankshaft Position Sensor A Circuit Shop $150–$400
You can drive it. Do not let it sit for months.
11 codesThe light is steady, so the car still runs. The cheap part is the one you replace now. Wait, and you buy the expensive one later.
- P0172 ≈1 month System Too Rich (Bank 1) Shop $100–$650
- P0121 ≈2 months Throttle Position Sensor Range / Performance Shop $200–$600
- P0171 ≈2 months System Too Lean (Bank 1) Shop $100–$600
- P0700 ≈2 months Transmission Control System Malfunction Shop $100–$3,000
- P0011 ≈3 months Camshaft Position Timing Over-Advanced (Bank 1) Shop $200–$900
- P0118 ≈3 months Engine Coolant Temperature Sensor Circuit High Shop $100–$250
- P0420 ≈3 months Catalyst System Efficiency Below Threshold (Bank 1) Shop $180–$1,200
- P0430 ≈3 months Catalyst System Efficiency Below Threshold (Bank 2) Shop $180–$1,200
- P0101 ≈6 months Mass Air Flow Sensor Range / Performance Shop $150–$500
- P0128 ≈6 months Coolant Thermostat Below Regulating Temperature Shop $150–$400
- P0135 ≈12 months O2 Sensor Heater Circuit (Bank 1 Sensor 1) Shop $150–$350
Safe to drive. It still fails a smog check.
4 codesEmissions gear. It will not strand you on the shoulder. It will fail an emissions test, and in a smog state that is a registration problem.
- P0113 ≈12 months Intake Air Temperature Sensor Circuit High Shop $100–$250
- P0442 ≈12 months Evaporative Emission System Leak Detected (Small Leak) Shop $80–$250
- P0455 ≈12 months Evaporative Emission System Leak Detected (Large Leak) Shop $80–$300
- P0456 ≈12 months Evaporative Emission System Leak Detected (Very Small Leak) Shop $90–$280
Where these numbers come from
Severity and drive windows
Built from NHTSA ODI complaint data, retrieved 2026-11. A window is a planning estimate, not a promise. Nobody can date a part from behind a screen.
Cost ranges
Parts catalogs, labor guides and owner reports, cross-checked across three source types. A field with no verified source stays blank instead of guessed.
Who writes this
Marcus Feld, an ASE-certified technician. He writes the diagnostic steps and reviews every code page before it ships.
Last updated 2026-11-11. A date changes only when the content changes, not to look fresh.