Owner's book · not a shop

Know the car. Then the window. Factory specs in plain English — don't authorize until you can say this at the counter.

Owner tools

Lab desks

No dongle required

Type the code

Any $20 scanner. Five characters. We write what it means and what to ask before parts. iPhone Safari has no Web Bluetooth — type the code.

Park first · Mode 03

ELM327

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P0171

soon · typical $80–$450; injectors only after a pressure/leak test

The computer is adding extra fuel because the mixture looks skinny. Vacuum leaks and dirty MAF beat 'bad injectors' on most first visits.

Usual first look · Vacuum leak, MAF, fuel pressure, PCV

Ask for short- and long-term fuel trims at idle vs 2500 RPM. A leak often shows only at idle.

Say this
I have P0171 stored. I want fuel trims at idle vs 2500 RPM before anyone prices injectors.

Safe to look at in the driveway (cap, boot, connector)

SAE layout: powertrain (engine / transmission). Subsystem looks like fuel and air metering. Generic (SAE) code.

This is an SAE-generic layout. The number is real even if our dictionary has no paragraph yet.

Paste the RO. Circle the line they hung on this pointer. The code is not a parts list.