Guide step
Know the baseline
Fuel trim near zero is normal. Large positive or negative corrections point to a root system issue.
Guide page
How to Read Live Fuel Trim Data Without Guessing
Use short-term and long-term fuel trim to separate vacuum leaks, sensor faults, and fuel delivery issues.
Guide step
Compare idle vs cruise
A vacuum leak often looks worse at idle, while fuel delivery issues may show more under load.
Guide step
Cross-check sensors
Always compare trim data with MAF, O2, and coolant readings before replacing parts.
Connected paths
Related codes
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P0171 — System Too Lean (Bank 1)P0174 — System Too Lean (Bank 2)P0172 — System Too Rich (Bank 1)P0101 — Mass Air Flow Circuit Range/PerformanceP0507 — Idle Control System RPM Higher Than ExpectedP0135 — O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)P0130 — O2 Sensor Circuit (Bank 1 Sensor 1)P0131 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)P0132 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)P0133 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)P0134 — O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)P0155 — O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)P0175 — System Too Rich (Bank 2)P0170 — Fuel Trim Malfunction (Bank 1)P0173 — Fuel Trim Malfunction (Bank 2)P2187 — System Too Lean at Idle (Bank 1)P2189 — System Too Lean at Idle (Bank 2)P2195 — O2 Sensor Signal Biased/Stuck Lean (Bank 1 Sensor 1)P2196 — O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 1)P2197 — O2 Sensor Signal Biased/Stuck Lean (Bank 2 Sensor 1)P2198 — O2 Sensor Signal Biased/Stuck Rich (Bank 2 Sensor 1)P0030 — HO2S Heater Control Circuit (Bank 1 Sensor 1)P0031 — HO2S Heater Control Circuit Low (Bank 1 Sensor 1)P0032 — HO2S Heater Control Circuit High (Bank 1 Sensor 1)P0050 — HO2S Heater Control Circuit (Bank 2 Sensor 1)P0051 — HO2S Heater Control Circuit Low (Bank 2 Sensor 1)P0052 — HO2S Heater Control Circuit High (Bank 2 Sensor 1)P2177 — System Too Lean Off Idle Bank 1P2179 — System Too Lean Off Idle Bank 2P1128 — Closed Loop Fueling Not Achieved Bank 1P1129 — Closed Loop Fueling Not Achieved Bank 2P1174 — Fuel Trim Cylinder Balance Bank 1P1101 — Mass Air Flow Sensor Out of Self-Test Range
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Related symptoms
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