System: Powertrain (P-Code)
SAE Standard (Generic)
Family: Fuel Composition Sensor Circuit
Code P0178: Fuel Composition Sensor Circuit Low
Diagnostic & Technical Explanation
Code P0178 (Fuel Composition Sensor Circuit Low) sets when the ECM sees an open, shorted, or implausible signal from the flex-fuel composition sensor, or determines the reported ethanol content is incorrect for observed fuel trim behavior. Causes are a failed sensor element, water/contamination in the fuel supply line to the sensor, or damaged sensor wiring.
First-listed procedure
Rank #1
Inspect fuel composition sensor connector and fuel supply
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 Composition Sensor Circuit
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)