Test Description
NOTE:
Test numbers refer to numbers on diagnostic chart.
- Codes P0171 and P0174 set at same time indicates both banks are operating lean. Inspect components/systems that could cause this condition (MAF, vacuum leak, fuel contamination, etc.).
- Visually/physically check exhaust for corrosion or loose or missing hardware, ensure pigtail is not contacting hot exhaust or ignition wires, repair misfires caused by ignition system, faulty injectors or engine mechanical problems, also check for vacuum leaks that will affect only bank 1 sensor. If bank 1 is operating lean, short term fuel trim will be near 138, and long term fuel trim will be near 155. These parameters are an average of all fuel trim cells.
- If fuel pressure is too low, system will go lean. Codes P0171 and P0174 may set if fuel pressure is too low.
- A lean condition will be caused if air pump is operating in closed loop.
- MAF sensor could cause a lean condition, but not set a MAF code. If lean condition no longer exists when MAF sensor is disconnected, replace MAF sensor. Visually/physically inspect both sensors for contamination. If contamination is evident, find cause of contamination (lead, silicone, heavy engine oil/coolant consumption, etc.).