System: Powertrain (P-Code)
SAE Standard (Generic)
Family: Fuel Trim Lean
Code P0171: System Too Lean Bank 1
Diagnostic & Technical Explanation
Code P0171 (System Too Lean Bank 1) sets when the ECM must add more fuel than the calibrated limit allows to correct a lean condition on the indicated bank. The leading causes are a vacuum or intake air leak downstream of the MAF, a weak fuel pump or clogged filter, or a leaking exhaust manifold gasket confusing the upstream O2 sensor.
First-listed procedure
Rank #1
Smoke-test intake for vacuum/air leaks
Easy DIY
This is the first procedure in the authored
consideration order, not a measured cause likelihood. Execute it only when its prerequisites
and diagnostic findings support it. Its cost and labor estimates (where known), the step-by-step procedure and the
remaining 2 procedure(s) are in the licensed dataset. Ordering context.
Full family: Fuel Trim Lean
What this page does not show
This page publishes the fault mechanism and the code index. The licensed dataset adds, for
every one of the 15,886 codes, the full authored repair set (56,729 procedures in total)
with the fields deliberately withheld here:
- Procedures 2..n after the first-listed procedure
- Aftermarket parts cost ranges in USD (
est_parts_cost_min/max_usd)
- Professional labor-hour estimates (
est_labor_hours)
- Step-by-step diagnostic and repair instructions
- Replacement-part mappings and catalog lookups
- 6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)