Code
P1170
GMC
P — Powertrain
Bank To Bank Fuel Trim Offset
AI status
Completed
Completed
100%
Causes
- Vacuum or intake manifold leak affecting one bank
- Leaking, clogged, or weak fuel injector(s) on one bank
- Faulty or slow oxygen sensor(s) (pre‑cat) on one bank
- Fuel supply issue causing uneven pressure or flow to a bank
- Exhaust leak between cylinders and O2 sensor on one bank
- Wiring/connectors or PCM input fault related to fuel/oxygen sensors or injectors
Symptoms
- Check Engine Light with P1170 stored (may be accompanied by related DTCs)
- Uneven or rough idle
- Reduced fuel economy
- Hesitation or stumble under load
- Possible misfire codes on the affected bank
- Failed emissions test or elevated tailpipe HC/NOx
What to check
- Connect a bi‑directional scan tool and record freeze frame and live data for Bank1/Bank2 STFT and LTFT, O2 sensor voltages, MAF/MAP, fuel pressure, RPM and engine load
- Compare LTFT and STFT values between banks during warm idle and under load
- Inspect intake manifold gasket, vacuum lines and PCV hoses for leaks; perform smoke test if needed
- Visually inspect wiring and connectors for O2 sensors and injectors on both banks
- Perform fuel pressure and flow test to confirm proper rail pressure and delivery
- Check O2 sensor response times and voltages (B1S1 vs B2S1) with scope or scan tool
Signal parameters
- Bank1 LTFT (%)
- Bank2 LTFT (%)
- Bank1 STFT (%)
- Bank2 STFT (%)
- Bank1 O2 sensor voltage(s) (pre‑cat)
- Bank2 O2 sensor voltage(s) (pre‑cat)
Diagnostic algorithm
- Retrieve DTCs and freeze frame data; note conditions when fault occurred.
- With engine at normal operating temperature, use a scan tool to monitor Bank1 and Bank2 STFT/LTFT and O2 sensor voltages at idle and under steady throttle. Confirm persistent offset between banks.
- Visually inspect intake, vacuum lines, PCV and intake manifold gasket for leaks; perform a smoke test to identify leaks that affect one bank.
- Inspect exhaust manifold and nearby pipes for leaks upstream of O2 sensors that could bias readings.
- Check wiring/connectors for O2 sensors and fuel injectors on both banks for corrosion, damage or poor connections.
- Test fuel pressure and flow; if uneven delivery is suspected, check regulator, rail, and supply to individual injectors.
- Perform injector balance or cylinder contribution test to identify weak or leaking injectors; consider swapping suspect injectors between banks to see if the condition follows the injector.
- Test O2 sensor response and crossover behavior; if a sensor is slow or biased, consider replacement or swap with the opposite bank to see if the code follows the sensor.
- If MAF/MAP readings appear incorrect, test and replace as needed, but prioritize bank‑specific faults first.
- Repair identified faults, clear codes, and perform road test and recheck trims and O2 sensor behavior to confirm repair.
- If no cause is found, inspect PCM inputs and grounding and consider professional diagnostic equipment or dealer resources.
Likely causes
- Vacuum leak or intake manifold gasket leak on one bank
- Leaking or clogged injector(s) on the affected bank
- Faulty pre‑catalyst O2 sensor on a bank (sensor reading slow or biased)
- Uneven fuel pressure or restricted fuel rail/feed to one bank
- Exhaust leak upstream of an O2 sensor causing false trim readings
Fault status
Status
PCM detected bank‑to‑bank long‑term fuel trim offset: the difference between Bank 1 and Bank 2 LTFT exceeded allowed threshold, indicating a persistent air/fuel imbalance between the two banks.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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