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Beginner · short stepsExpert · spec · code · mm

The light is a pointer. Do not throw parts.

Dictionary + likely systems. Freeze-frame before parts. P0300 is not a coil kit.

WhoAudience: Anyone with a P/B/C/U on a $20 scanner.Owners and techs who want the test order.
ClickControl: Type the code. Read the English. Stop at the inspect list.Code in the box. Optional ?code= on the URL.
SayCounter: P0420 is not automatically a converter. What test first?Freeze-frame first. Then the circuit test. Then parts.

Codes · 270 in the book

Do not throw parts

Android Chrome can pull Mode 03 from a BLE ELM327. iOS Safari has no Web Bluetooth — type the code or use TestFlight native. P0420 is not a converter. P0300 is not a coil kit.

Park first · Mode 03

ELM327

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P0171

System too lean (Bank 1)

soon

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

Likely systems

vacuum / intake leak
MAF
fuel pressure
PCV

Do not throw parts · Do not throw injectors or a cat. Ask for short- and long-term fuel trims at idle vs 2500 RPM.

First look · Trims at idle vs 2500. 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.

powertrain (engine / transmission / hybrid). Subsystem looks like fuel and air metering. Generic (SAE) code. SAE-generic layout. The number is real even if our paragraph is missing.

Take P0171 to quote defense

The light is a pointer. Paste the RO and circle the line they hung on this code.

Do not throw parts

ELM327

Type the scanner code

System too lean (Bank 1)

Do not throw parts

ELM327

Type the scanner code

System too lean (Bank 1)