OBD-II Code P1273: Air-Fuel Mixture Problem (Bank 1)

What Does P1273 Mean?

P1273 indicates your engine's Engine Control Module (ECM) detects an air-to-fuel ratio problem on 'Bank 1'. Specifically, the mixture runs 'lean'—meaning there is too much air and not enough fuel. This code predominantly affects Nissan and Infiniti vehicles. However, OBD-II codes are manufacturer-specific; on a Ford 7.3L PowerStroke diesel, P1273 indicates an electrical fault in an injector circuit, not a lean condition.

Technical definition: The SAE/OBD-II definition for this manufacturer-specific code is 'Air Fuel Ratio (A/F) Sensor 1 Bank 1 Lean Shift Monitoring'. The ECM detects a consistently lean mixture based on primary air-fuel ratio sensor feedback. For other manufacturers, definitions vary wildly, such as 'Cylinder #3 High to Low Side Open' on Ford diesels or 'Pump-Injector Valve Regulation Range Exceeded' on Volkswagen TDIs.

Can I Drive With P1273?

Yes, But With Caution. You can drive temporarily, but prolonged driving destroys catalytic converters. Ignoring it causes poor gas mileage, failed emissions tests, and turns a minor repair into a $1,500 to $2,500 converter replacement. On 2002-2006 Nissan 2.5L engines, this code precedes pre-catalyst failure, which destroys the engine if ignored.

Common Causes

• Faulty Air/Fuel Ratio Sensor (Bank 1, Sensor 1) (Very Common) — This is the most frequent cause on Nissan and Infiniti vehicles. The wideband oxygen sensor wears out over time, loses calibration, and sends falsely lean signals to the computer.
🎬 Watch: How to test and replace the Bank 1 sensor.
• Exhaust System Leaks (Common) — Cracks in the exhaust manifold or blown gaskets before the A/F sensor pull unmetered oxygen into the exhaust stream. The sensor reads this extra oxygen and incorrectly reports a lean condition.
• Vacuum and Intake Leaks (Common) — Cracked vacuum hoses, a stuck-open PCV valve, or loose intake manifold bolts allow unmeasured air to bypass the mass airflow sensor. On Infiniti G35s, loose plenum bolts are a notorious trigger.
• Cracked Pre-Catalytic Converter (Common On Specific Models) — On 2002-2006 Nissan Sentra and Altima 2.5L engines, the catalytic converter integrated into the exhaust manifold disintegrates. This creates an exhaust restriction and leak, triggering the code and risking catastrophic engine damage if ceramic debris is sucked into the cylinders.
• Dirty or Faulty Mass Airflow (MAF) Sensor (Less Common) — A contaminated MAF sensor under-reports the amount of air entering the engine. The computer responds by withholding fuel, creating a genuine lean condition.
• Low Fuel Pressure (Less Common) — A weak fuel pump, failing pressure regulator, or clogged fuel filter starves the engine of fuel. On many Nissan models, fuel pressure dropping below 51 psi triggers this code.
• Incompatible Aftermarket Modifications (Less Common) — High-flow catalytic converters, test pipes, or improperly sealed cold air intakes alter airflow and backpressure beyond the ECM's factory parameters, requiring an ECU tune to resolve.
• Leaking or Clogged Fuel Injectors (Rare) — A clogged fuel injector on Bank 1 restricts fuel delivery to a specific cylinder, contributing to a lean reading for that entire bank.
• Faulty Engine Control Module (ECM) (Very Rare) — The ECM itself fails and misinterprets sensor data. Rule out all mechanical and sensor faults before replacing the computer.

Symptoms

• Check Engine Light is On — The malfunction indicator lamp illuminates immediately when the ECM detects the lean shift.
• Poor Gas Mileage — Fuel economy drops by 10% to 20% because the computer constantly over-fuels the engine to correct the perceived lean condition.
• Rough Idle or Hesitation — The engine stumbles at idle or hesitates during acceleration due to the imbalanced air-fuel mixture.
• Engine Ticking or Exhaust Leak Noise — A rhythmic ticking sound from the engine bay on cold starts indicates an exhaust manifold leak, a primary cause of P1273.
• Failed Emissions Test — The vehicle automatically fails OBD-II smog checks, and the lean condition increases tailpipe NOx emissions.
• High Positive Fuel Trims (scan-tool only — no driver-felt sign) — Long-Term Fuel Trim (LTFT) for Bank 1 exceeds +15% on a scan tool as the ECM dumps extra fuel into the engine to compensate for the lean reading.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Replace Air/Fuel Ratio Sensor (Bank 1, Sensor 1) — Parts: $75 - $300, Labor: $100 - $250, ~1.5 hr book time (DIY)
• Repair Exhaust Leak — Parts: $20 - $1,200, Labor: $150 - $600, ~3.5 hr book time (Professional)
• Repair Vacuum Leak — Parts: $5 - $100, Labor: $75 - $200, ~1.2 hr book time (DIY)
• Clean or Replace Mass Airflow (MAF) Sensor — Parts: $10 - $350, Labor: $0 - $100, ~0.5 hr book time (DIY)
• Replace Fuel Pump — Parts: $300 - $1,500, Labor: $150 - $300, ~2.5 hr book time (Professional)
• Repair Ford Injector Circuit Fault — Parts: $30 - $150, Labor: $250 - $500, ~2.5 hr book time (Intermediate)

Used vs. New Parts: Buying Guide

When a used part is worth it: Never buy a used A/F sensor. A used OEM catalytic converter from a low-mileage (under 80k miles) donor vehicle is a cost-effective alternative to cheap aftermarket converters.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the donor vehicle was salvaged for a collision, not engine failure.
• Match the part number exactly; visual similarity is insufficient.
• Inspect the converter for external damage, heavy rust, or internal rattling.

Decision logic:

• If The part is an A/F sensor or MAF sensor → Buy new from an OEM supplier like Denso or Hitachi. Used sensors are a waste of labor.
• If The part is a catalytic converter and the vehicle is over 150K miles → A used OEM converter from a low-mileage donor outperforms cheap new aftermarket converters.
• If You live in a CARB-compliant state (CA, NY, CO) → Buying used converters is illegal. You must purchase a new CARB-compliant part.

Warranty tradeoff: Used parts carry a 30-day warranty. New aftermarket parts offer 1-year warranties. New OEM parts carry the manufacturer's standard warranty.

Worst-case if a used part fails: $300-$800 if a used converter fails, requiring repeat labor and a second part purchase.

What Happens If You Wait — Timeline

1. 0-2 weeks: Check Engine Light illuminates. No noticeable symptoms. Fuel trims elevate as the ECM compensates. (MPG impact: 0-5%% · Added cost: $0)
2. 2 weeks - 3 months: Fuel economy drops noticeably. Engine hesitates on acceleration. The ECM commands maximum fuel trims (+15% or more). (MPG impact: 5-15%% · Added cost: $50-$150 in wasted fuel)
3. 3-8 months: Constant over-fueling overheats the catalytic converter. The internal ceramic substrate cracks and melts. P0420 code appears. (MPG impact: 10-20%% · Added cost: $1,500 - $2,800 for catalytic converter replacement)
4. 8+ months (Nissan 2.5L specific): The disintegrating pre-catalyst is sucked back into the engine. Ceramic debris scores cylinder walls, causing massive oil consumption and engine death. (MPG impact: 20%+% · Added cost: $4,000 - $8,000 for engine replacement)

Cost of Not Fixing It

• 0-1 month: Reduced fuel economy (10-15% drop) and failed emissions test. Noticeable hesitation or rough idle. (Added cost: $20-$60 per month in extra fuel)
• 1-6 months: The lean mixture causes the catalytic converter to overheat, leading to internal melting and permanent failure. (Added cost: $1,500 - $2,800 for catalytic converter replacement)
• 6+ months: On Nissan 2.5L engines, the pre-catalyst breaks apart, sending ceramic debris into the engine, scoring cylinder walls and causing catastrophic engine failure. (Added cost: $4,000 - $8,000 for a replacement engine)

Diagnosis Steps

1. Check for Other Codes & Freeze Frame Data
   Read all present codes and view the freeze frame data. The freeze frame shows engine RPM, speed, and temperature when the code set. If P1283 (Bank 2 Lean) is also present, you have a global issue like a vacuum leak or bad MAF, not a single bad sensor.
   Tools: OBD-II Scanner (Beginner)
2. Analyze Live Fuel Trim Data (Pro Tip)
   Monitor Short-Term (STFT) and Long-Term Fuel Trim (LTFT) for Bank 1 at idle and at 2500 RPM. If trims are high (+15%) at idle but drop to normal (0-5%) at 2500 RPM, you have a vacuum leak. If trims stay high across all RPMs, suspect a MAF sensor or fuel delivery issue.
   Tools: OBD-II Scanner with Live Data (Advanced)
3. Test the Air/Fuel Ratio Sensor
   Monitor the Bank 1 Sensor 1 A/F sensor voltage on a graphing scanner. On Nissans, voltage fluctuates steadily around a baseline (often 1.5V or 2.2V depending on the tool). A sensor stuck at a high voltage or showing a lazy response is faulty.
   Tools: Graphing Scan Tool (Advanced)
4. Inspect for Vacuum & Intake Leaks
   Visually inspect all vacuum hoses, the PCV system, and the air intake tube. Use a smoke machine to feed pressurized smoke into the intake and watch for escapes. Alternatively, spray short bursts of brake cleaner around suspected leaks while idling; an RPM surge confirms a leak.
   Tools: Smoke Machine or Brake Cleaner, Flashlight (Intermediate)
5. Inspect for Exhaust Leaks
   Start the engine cold and listen for puffing or ticking sounds from the exhaust manifold and pre-catalyst. Feel around the manifold flanges for escaping air before the metal heats up and expands to seal the crack.
   Tools: Gloves, Flashlight (Intermediate)
6. Clean the Mass Airflow (MAF) Sensor
   Remove the MAF sensor from the intake tube. Spray the delicate internal wires with dedicated MAF sensor cleaner. Never touch the wires. Let it dry completely before reinstalling.
   Tools: Screwdriver, MAF Sensor Cleaner (Beginner)
7. Check for Pre-Catalyst Failure (Nissan 2.5L)
   For 2002-2006 Nissan Sentra/Altima models, remove the upstream A/F sensor and insert a borescope into the exhaust manifold. Inspect the ceramic honeycomb for melting, cracking, or missing chunks.
   Tools: Borescope, O2 Sensor Socket (Advanced)
8. Test Fuel Pressure
   Connect a fuel pressure gauge to the fuel rail test port. Verify pressure meets manufacturer specs (typically 51-52 psi for 2000s Nissans). Low pressure indicates a failing fuel pump or clogged filter.
   Tools: Fuel Pressure Gauge (Intermediate)
9. Test A/F Sensor Heater Resistance
   Disconnect the A/F sensor and measure resistance across the two heater pins (usually the two same-colored wires) with a multimeter. A healthy heater reads 2 to 5 ohms. An infinite (OL) reading means the sensor is dead.
   Tools: Multimeter (Advanced)
10. Test Injector Circuit (Ford 7.3L Only)
    If working on a Ford 7.3L diesel, perform an injector buzz test. Disconnect the Under-Valve-Cover (UVC) harness and measure resistance across the #3 injector pins. A healthy coil reads 3.0 to 4.0 ohms. An open circuit requires harness or injector replacement.
    Tools: Advanced Scan Tool, Multimeter (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 175-210°F (Fully warmed up)
• RPM: 1500-2500 (Cruise / steady throttle)
• Engine Load: 25-50% (Light to moderate acceleration or steady cruising)
• Vehicle Speed: 40-65 mph (Highway or arterial road driving)

Related Codes

• P1283 — The identical code for Bank 2. Seeing P1273 and P1283 together guarantees a global engine issue (MAF sensor, major vacuum leak, fuel pressure) rather than a single bad sensor.
• P0171 — The generic code for 'System Too Lean (Bank 1)'. P1273 is Nissan's early warning code; P0171 sets when fuel trims hit their absolute maximum limit.
• P0300 — Random Misfire Detected. A severe lean condition prevents consistent ignition, causing misfires. Fixing the P1273 root cause resolves the misfires.
• P0420 — Catalyst Efficiency Below Threshold. On Nissan 2.5L engines, seeing P1273 and P0420 together confirms the pre-catalyst is disintegrating.

Climate & Environmental Factors

• Cold Weather: Cold temperatures exacerbate exhaust leaks. A cracked manifold leaks heavily on cold starts, triggering the code, but seals up as the metal heats and expands.
• High Altitude: Less dense air at high altitudes exposes borderline MAF sensors or weak fuel pumps, pushing fuel trims past their limits and triggering lean codes.
• High Humidity: Humidity displaces oxygen, causing a slight lean shift. Modern ECMs compensate easily, making this a rare primary cause.

How to Talk to a Mechanic About This Code

Say this: "I have a P1273 code on my Nissan and need an hour of diagnostic time. Please check live fuel trims and inspect for vacuum or exhaust leaks before recommending an A/F sensor replacement."

This proves you are an informed customer. It forces the mechanic to perform a proper diagnosis rather than firing the parts cannon at the most obvious sensor.

Avoid saying:

• 'Just fix whatever's wrong'
• 'My check engine light is on, can you look at it?'
• 'I think it's the oxygen sensor, can you just replace it?'

Questions to ask before authorizing the repair:

• What were the long-term fuel trim readings at idle versus 2500 RPM?
• Did you find any vacuum or exhaust leaks? Can you show me?
• Does the estimate include performing the Nissan 'Air Fuel Learning' reset procedure?
• What brand of A/F sensor are you installing? (Demand OEM Denso or Bosch)

Where to Take It: Dealer vs Independent vs Chain

• Dealer: A safe but expensive option. Best for owners who prioritize a guaranteed fix over cost, as dealers possess the exact software for the mandatory reset.
  Best for: Vehicles under emissions warranty, Ensuring the proprietary Nissan 'Air Fuel Learning' reset is performed correctly.
  Downsides: Labor rates are 50% to 100% higher than independent shops., Dealers default to replacing entire expensive assemblies rather than repairing small leaks. (Typical cost: +50% vs. baseline)
• Independent Shop: The best choice for most owners. Ensure the shop specializes in imports and explicitly ask if their scanners can perform the Nissan 'Air Fuel Learning' reset.
  Best for: Out-of-warranty vehicles where cost is a factor., Shops specializing in Japanese imports.
  Downsides: May lack the specific scanner software to perform the Nissan reset procedure. (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid. Chain shops will replace the A/F sensor, skip the reset procedure, and hand the car back, guaranteeing the code returns.
  Best for: Tires, brakes, and oil changes.
  Downsides: Technicians lack advanced diagnostic training., High likelihood of misdiagnosing P1273 by simply replacing the sensor and ignoring leaks. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the repair cost exceeds 50% of your car's private-party value, sell or trade it in.

• Car worth $3000, fix is $2500: Walk away. A $2,500 pre-catalyst replacement on a $3,000 car is a terrible financial decision.
• Car worth $10000, fix is $350: Fix it. A $350 sensor replacement is a minor maintenance cost.
• Car worth $4500, fix is $2200: Borderline. Get a second opinion. If the engine is already burning oil from pre-cat debris, walk away.

What Scan Tool You Need for This Code

Minimum: A scanner that graphs live data, specifically Long-Term Fuel Trims (LTFT) and A/F sensor voltage.

A $20 code reader only provides the P1273 code. Without live fuel trim data, you cannot distinguish between a vacuum leak, a bad sensor, or a failing fuel pump.

Budget: BlueDriver Pro (~$99) — Connects via Bluetooth and provides excellent live data graphing for fuel trims and sensor voltages. Perfect for diagnosing the root cause.

Mid-range: Foxwell NT510 Elite (~$180) — A bi-directional tool that accesses manufacturer-specific functions, including the mandatory Nissan 'Air Fuel Learning' reset.

Professional: Autel MaxiCOM MK808 (~$500) — Provides professional-level bidirectional control and guaranteed access to all OEM resets and active tests.

Rent vs buy: Buy. Free rental scanners from auto parts stores cannot graph live data or perform the Nissan reset procedure.

How to Clear the Code After You Fix It

1. Fix the underlying mechanical or electrical fault.
2. For Nissan/Infiniti, perform the mandatory 'Air Fuel Learning' reset procedure.
3. Use an OBD-II scan tool to clear all diagnostic trouble codes.
4. Perform a complete drive cycle to allow all emissions readiness monitors to run.

Drive cycle (~30 minutes): Cold start and idle for 3 minutes. Drive in stop-and-go traffic for 15 minutes. Drive at a steady highway speed (55-65 mph) for 15 minutes. Let the vehicle sit overnight to complete the EVAP monitor test.

Readiness monitors affected: Catalyst Monitor, Oxygen Sensor Monitor, Oxygen Sensor Heater Monitor, EVAP System Monitor

Before emissions retest: drive at least 100 miles to fully set monitors.

Watch out for:

• On Nissans, clearing the code without performing the 'Air Fuel Learning' reset guarantees the code will return.
• Disconnecting the battery clears codes but resets all readiness monitors to 'Not Ready', causing an automatic emissions failure.
• Replacing the sensor without fixing an underlying exhaust leak results in immediate code recurrence.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An active P1273 is an automatic failure. After repairs, a full drive cycle (50-100 miles) must be completed to set readiness monitors before retesting.
• New York: The NYS DMV inspection includes an OBD-II scan. Any check engine light results in immediate failure.
• Texas: In the 17 counties requiring emissions testing, an active P1273 code fails the OBD-II inspection.

Most Commonly Affected Vehicles

• Nissan Altima (2002-2006) — Extremely common on 2.5L QR25DE engines. Often caused by pre-catalyst failure, which destroys the engine if ignored.
• Nissan Sentra (2002-2006) — The 2.5L SE-R models suffer from the same catastrophic exhaust manifold/pre-cat disintegration issues as the Altima.
• Infiniti G35 (2003-2007) — Frequently appears alongside P1283. Caused by vacuum leaks (loose intake plenum bolts) and faulty A/F sensors.
• Nissan Maxima (2004-2008) — Routinely triggered by failing A/F sensors or cracked vacuum hoses.
• Ford F-250/F-350 Super Duty (1999-2003) — On the 7.3L PowerStroke diesel, P1273 means 'Cylinder #3 High to Low Side Open,' an injector electrical fault, not a lean condition.
• Volkswagen Touareg / Jetta (TDI) (2004-2006) — On VW TDI diesels, P1273 indicates an issue with the pump-injector valve for cylinder 5 exceeding its regulation range.

Manufacturer-Specific Notes

• Nissan / Infiniti: Per TSB NTB04-126, you must perform an 'Air Fuel Learning' reset after repairs. Disconnect the MAF, idle for 5 seconds, reconnect, clear codes, and idle for 10 minutes. Skipping this guarantees the code returns.
• Nissan / Infiniti: These ECMs are hyper-sensitive to exhaust leaks. A hairline crack in the manifold or installing aftermarket high-flow cats instantly triggers P1273.
• Nissan: Nissan issued warranty extensions for 2002-2006 2.5L engines due to pre-catalyst failure. While expired, TSB NTB05-065c proves this is a factory defect requiring immediate attention.
• Ford (7.3L PowerStroke): P1273 is strictly an electrical fault for the #3 fuel injector. The Under-Valve-Cover (UVC) wiring harness melts from engine heat, breaking the circuit.
• Infiniti (G35): Aftermarket intake plenum spacers are popular mods, but the bolts loosen over time, creating massive vacuum leaks that trigger P1273 and P1283.

Real Owner Stories

2004 Infiniti G35 Coupe - The Misdiagnosis Chase

Check Engine Light came on with P1273. Mechanic replaced the Bank 1 A/F sensor. Light returned 30 miles later, now with both P1273 and P1283 (Bank 2 lean).

What they tried:

1. Cleared codes (returned).
2. Cleaned MAF sensor (returned).
3. Mechanic checked for intake/exhaust leaks but found none.

Outcome: The single-bank code evolved into a dual-bank code, proving the initial sensor replacement was wrong. The root cause was a failing fuel pump starving both banks of fuel.

Lesson: When P1273 turns into P1273 & P1283 after a repair, you have a global issue affecting the whole engine. Stop replacing sensors and test fuel pressure and the MAF sensor.

2004 Nissan Sentra - The Simple (and Dangerous) Leak

P1273 code appeared with no driving symptoms. Owner noted a small exhaust leak from the flex pipe but ignored it.

What they tried:

1. Cleared the code (returned in 7 miles).
2. Replaced air filter (returned in 500 miles).

Outcome: After months, the owner replaced the leaking flex pipe. The P1273 code resolved immediately and did not return.

Lesson: Nissan ECMs are hyper-sensitive. A tiny 'ticking' exhaust leak before the oxygen sensors pulls in air and triggers a lean code. Fix exhaust leaks before buying sensors.

Modified Infiniti G35 - When Mods are the Problem

Owner with high-flow cats, straight pipe, plenum spacer, and cold air intake triggered P1273 and P1283.

What they tried:

1. Replaced all 4 O2 sensors.
2. Replaced all vacuum hoses.
3. Replaced fuel pump.
4. Performed Air/Fuel Learning reset.

Outcome: After eliminating all mechanical faults, the owner realized the combination of modifications pushed airflow beyond the stock ECU's limits. A professional ECU tune resolved the codes.

Lesson: Aftermarket parts that drastically alter airflow require an ECU tune. If you have bolt-on mods and persistent lean codes, the factory computer simply cannot compensate.

How to Prevent This Code From Triggering

• Use Top Tier certified gasoline. (Every fill-up) — High detergent levels prevent injector clogging, ensuring proper fuel atomization and preventing lean conditions.
• Replace engine air filter. (Every 15,000-30,000 miles) — Prevents debris from bypassing the filter and contaminating the delicate MAF sensor wires.
• Fix engine oil and coolant leaks immediately. (As needed) — Burning oil or coolant poisons the A/F sensor and catalytic converter, drastically shortening their lifespan.

Frequently Asked Questions

What is Bank 1?

On a 4-cylinder engine, there is only one bank (Bank 1). On a V6 or V8, Bank 1 is the side of the engine containing cylinder #1. Consult your repair manual to identify which side is Bank 1 for your specific vehicle.

What is an Air/Fuel Ratio Sensor?

It is an advanced wideband oxygen sensor that measures the exact air-to-fuel ratio in the exhaust. It uses a pumping current to maintain a perfect ratio internally, and the required voltage tells the ECM exactly how rich or lean the engine is running.

What are the most common misdiagnosis mistakes for P1273?

The biggest mistake is replacing the A/F sensor without checking for vacuum or exhaust leaks first. On Nissans, failing to perform the mandatory 'Air Fuel Learning' reset after replacing the sensor guarantees the code will return.

My P1273 code appeared after installing an aftermarket exhaust or intake. What's wrong?

This is common. Check for vacuum leaks around new intakes, or MAF sensor contamination from oiled filters. Aftermarket exhaust parts alter airflow and backpressure, confusing the A/F sensor and often requiring an ECU tune to resolve.

Why did the code come back after I replaced the sensor?

On Nissans, you likely skipped the mandatory 'Air Fuel Learning' reset, so the computer is using old data. Otherwise, you installed a cheap aftermarket sensor, or the real issue is an undiagnosed vacuum or exhaust leak.

How much does it cost to fix code P1273?

A DIY vacuum hose replacement costs under $20. A professional A/F sensor replacement runs $175 to $550. Replacing a cracked exhaust manifold with an integrated pre-catalyst costs over $1,000 at a shop.

Can I pass an emissions test with code P1273?

No. An active P1273 code triggers an automatic failure for OBD-II smog inspections. The lean condition also spikes NOx emissions, guaranteeing a tailpipe test failure.

Key Takeaways

• On Nissan and Infiniti vehicles, P1273 indicates Bank 1 of your engine is running lean (too much air, not enough fuel).
• A faulty Air/Fuel Ratio Sensor causes 70% of P1273 codes, followed closely by exhaust manifold cracks and vacuum leaks.
• You must perform Nissan's specific 'Air Fuel Learning' reset procedure after repairs, or the ECM will retain old data and trigger the code again.
• Ignoring P1273 drops fuel economy by up to 15% and destroys catalytic converters, turning a $200 sensor replacement into a $2,000+ repair.
• P1273 is manufacturer-specific; on a Ford 7.3L diesel, it indicates an electrical fault in the #3 fuel injector circuit, not a lean condition.