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P1171

Fuel System Lean During Acceleration.

  • Saturn
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
1
AreaFuel and air metering
71
FaultThe specific fault in that area

What it means

P1171 on a Saturn means the engine control module saw the fuel system running lean while the car was accelerating. The fuel trim and oxygen sensor readings showed the mixture going lean when the engine was under load and demanding more fuel. The fault points to a fuel delivery, air metering or leak problem rather than a single failed part.

Symptoms

  • Hesitation, stumble or flat spot when accelerating
  • Malfunction indicator lamp on
  • Lack of power under load or when overtaking
  • Surging or misfire under acceleration
  • Rough running or poor drivability
  • Poor fuel economy in some cases

Possible causes

  • Vacuum leak or unmetered air entering after the air flow sensor, such as split hoses, intake boot or manifold gasketlikely
  • Restricted fuel filter or weak fuel pump unable to hold pressure under loadlikely
  • Dirty or faulty mass air flow sensor under-reporting airflowlikely
  • Clogged, leaking or failing fuel injectorspossible
  • Faulty fuel pressure regulatorpossible
  • Exhaust leak ahead of the oxygen sensor giving a false lean readingpossible
  • Faulty oxygen sensor or wiring and connector problemrare

How to diagnose

  1. Read stored and pending codes and the freeze frame data to see load, rpm, coolant temperature and fuel trim values when the fault set
  2. Check for other related codes such as misfire, MAF or oxygen sensor faults and deal with those first
  3. Inspect vacuum hoses, intake ducting, clamps and connectors for splits, loose fittings and damage
  4. Check live short and long term fuel trims at idle and at 2,500 rpm; a trim that is high at idle and improves with load suggests a vacuum leak, while a trim that worsens under load suggests a fuel supply issue
  5. Compare the MAF sensor reading with expected values at idle and inspect the sensor element for contamination
  6. Test fuel pressure and volume at idle and under load against the specification for the specific engine
  7. Check the fuel pressure regulator and inspect for exhaust leaks before the upstream oxygen sensor
  8. Check injector operation and spray pattern or balance; procedure depends on the engine fitted

How to fix

  • Repair or replace any leaking vacuum hoses, intake boots or gaskets
  • Replace the fuel filter if restricted, or the fuel pump if pressure or flow is low
  • Clean or replace the MAF sensor if it is contaminated or faulty
  • Clean or replace faulty fuel injectors
  • Replace a faulty fuel pressure regulator
  • Repair exhaust leaks and replace the oxygen sensor or repair its wiring only if testing shows it at fault

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but a lean mixture can cause misfire, overheating and catalyst damage, so book it in soon. Avoid heavy acceleration or towing until it is repaired.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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