Global Fault Code
Free · no signupP0171 / P0174
Hesitation on acceleration; Hissing sound from engine; Lean misfires; Poor idle.
System
Not specified
Symptom
Hesitation on acceleration; Hissing sound from engine; Lean misfires; Poor idle.
Diagnosis & fix steps
System Too Lean (Bank 1 or 2).
LOGIC: The Oxygen sensor sees too much unburned oxygen. The PCM has reached its +25% fuel trim limit trying to compensate.
ACTION: 1. Check for vacuum leaks (PCV/Intake).
2. Inspect Mass Air Flow (MAF) sensor for dirt.
3. Test fuel pump pressure.
FIX: Clean MAF sensor; replace cracked intake boots; replace fuel pump/filter.
Red Seal field insights
If the code goes away at high RPM, it's a vacuum leak. If the code gets worse at high RPM, it's a fuel delivery (pump/filter) or dirty MAF sensor issue.
Same code keeps coming back?
That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.
Read before you touch anything
- This is general reference information, not a repair manual. It is for trained, qualified technicians.
- Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
- Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
- You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
- Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.
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