P0171 on Mitsubishi: How to Diagnose & Fix
System Too Lean (Bank 1)
1 Mitsubishi model · 1 documented issue · $75-$400 repair
P0171 on Mitsubishi by model: symptoms, diagnosis and fix
On 1995-1999 cars the fuel pump's factory wiring is undersized and its chassis ground (at the floor crossmember under the driver's seat) corrodes with age, dropping voltage at the pump into the 10-11V range under load. The paired fuel pump/MFI relay behind the center console can also fail. The result is intermittent cranking no-starts (no pump prime), stalling, and lean stumble or fuel cut at wide-open throttle on turbo cars — a problem so common the community-standard fix is the documented 'fuel pump rewire.'
Common Symptoms
- Engine cranks but fuel pump never hums
- Intermittent no-start, often after heat soak
- Stalling or dying while driving
- Lean stumble or fuel cut at wide-open throttle
- Fuel pressure/voltage at the pump drops under load
How to Fix
Test voltage at the pump and the fuel pump/MFI relay first; replace the relay if it fails continuity testing, and repair or supplement the corroded ground wire. The accepted long-term fix is the DSM fuel pump rewire: a relay-triggered, fused 12-gauge feed direct from the battery/alternator with a fresh chassis ground.
Sources for this issue (7)
- 2G - MFI/Fuel Pump Relay (relay failure, testing, 95 vs 96-99 part numbers)forum
- Resolved - 99 GST Fuel pump not turning on (confirms corroded floor-crossmember ground under driver's seat, fixed by new chassis ground)forum
- 2G AWD fuel pump rewire info - DSMTalkforum
- 2G Fuel Pump Rewire, Pictorial with Diagram (canonical community-standard fix writeup)forum
- Mitsubishi Eclipse Questions - Fuel pump not getting power to it - CarGurusforum
- 2g GS-T (FWD) & GSX (AWD) Fuel Pump Rewire Diagramforum
- 2G AWD Fuel Pump Rewire w/ STM kit (commercial rewire kit exists for this exact problem)forum
P0171 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0171 mean on a Mitsubishi?
P0171 stands for "System Too Lean (Bank 1)." This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered. On Mitsubishi it is documented across 1 model: Eclipse.
What are the most common causes of P0171?
The most common causes of P0171 are: Vacuum or intake air leak (cracked hose, gasket, or PCV system), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter, Clogged or dirty fuel injectors, Faulty or aged upstream oxygen sensor, Leaking intake manifold gasket, Low fuel pressure or failing fuel pressure regulator, Exhaust leak ahead of the oxygen sensor. The specific cause varies by vehicle.
How much does it cost to fix P0171 on a Mitsubishi?
Published repair estimates on Mitsubishi range from $75 to $400 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0171 on a different make?
View P0171 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.