P0171 on a 2018-2019 Toyota Camry 2.5L: Lean? Fix Other Codes, Then Test Fuel Pressure
JC Landry, ASE Master TechnicianPublished Oct 26, 2026 · Updated Oct 30, 2026
P0171 on a 2018-2019 Toyota Camry 2.5L (A25A-FKS) means the ECM has pushed combined fuel trim to plus 35 percent or more on bank 1 to fight a lean mix. Repair any other stored codes first, because they block the lean check. A fuel pressure check and the injection mode test narrow it down; I would rule out the in-tank fuel pump first. If the car stalls or runs rough, stop driving it.
Safety first
- Keep ignition sources away, disconnect the negative battery cable and discharge fuel pressure before opening any fuel line; cover the line with a cloth.
- Stay off hot engine and exhaust parts at the sensor.
- In the EGR test, do not hold the valve open 10 seconds or more or open it 30 steps or more.
- Obey traffic laws on the confirmation drive.
What does P0171 mean on a 2018-2019 Camry?
P0171 (System Too Lean Bank 1) is the fuel trim check on the 2.5L four-cylinder. The ECM reads exhaust oxygen content from air fuel ratio sensor 1, in the exhaust manifold at the front catalyst, and adds fuel when the mix reads lean or cuts it when it reads rich; long term trim learns any lasting offset. When the combined average runs past the limit, the ECM decides the engine is getting more air or less fuel than calculated.
The ECM sets P0171 when the average of short and long term trim reaches plus 35 percent or higher, engine warm and feedback stable, and the check runs continuously within 10 seconds. All of these must hold:
- Fuel system status is closed loop.
- Battery voltage is 11 V or higher.
- Engine speed is below 800 rpm, or engine load is 12 percent or higher.
- The catalyst monitor is not running, and the EVAP purge cut is active.
- None of the fix-first codes in the diagnosis are stored.
P1170 and P117B are a second step, evaluated only once a fuel system code has set, with the EVAP purge cut active and the other injection system carrying 100 percent of the fuel (direct for P1170, port for P117B). Either sets when average trim sits inside the normal window (below plus 35 and above minus 35 percent), so P1170 points at the port side and P117B at the direct side.
P0172 (System Too Rich Bank 1) is the same check at minus 35 percent or lower. P0171 and P0172 use two trip detection, so the light comes on at the second detection; P1170 and P117B use one trip, store the code and leave the light off.
What symptoms does P0171 cause on the Camry?
- Check engine light on
- Hard starting
- Positive fuel trim values on the scan tool
- Rough or unstable idle
- Surging or hesitation
What causes P0171 on the Camry, most likely first?
| Rank | Cause | Quick confirm | Typical fix |
|---|---|---|---|
| 1 | In-tank fuel pump not delivering enough pressure | Low-side fuel pressure check with a gauge | Replace the pump if pressure is out of specification and the line is clear; check your VIN for recalls first |
| 2 | Air leak after the air flow meter | PCV hose, PCV valve and intake vacuum leak checks | Repair or replace the part |
| 3 | Fuel injector, direct or port | Injection mode test; direct mode misfire count by cylinder | Replace the failing injector, or the high-pressure pump if misfires are not in one cylinder and pressure is out of range |
| 4 | Mass air flow meter dirty, reading off, or poor connection | Air flow reading at 3,000 rpm in park, warm, A/C off | Clean the meter, repair the connector, or replace the meter |
| 5 | Air fuel ratio sensor 1 or its circuit | Injection volume active test; sensor current follows the swings | Replace sensor 1 after heater, power and wiring checks pass |
Toyota service bulletin T-SB-0009-23 covers loss of fuel pressure with P0171 on certain 2018-2020 Camry models and starts with the same pressure check as cause number 1.
How do you diagnose P0171 on a 2018-2019 Camry?
You need a scan tool that runs Toyota active tests. Check the fuses first.
- 1
Read every stored code.
Anything other than P0171, P0172, P1170 or P117B gets repaired first, because the lean monitor will not run with these stored:
- Variable valve timing P0010, P0011, P0012, P0013, P0014, P0015, P0016, P0017, P1360, P1362, P1364, P1366, P2614
- Air fuel ratio sensor 1 heater P0031, P0032, P101D
- Mass air flow meter P0101, P0102, P0103
- Manifold absolute pressure P0107, P0108
- Coolant temperature P0117, P0118, P0125
- Throttle position P0121, P0122, P0123, P0222, P0223, P2135
- High-pressure side fuel pressure sensor P0191, P0192, P0193
- Low-pressure side fuel pressure sensor P107B, P107C, P107D
- Fuel injectors P0201, P0202, P0203, P0204, P062D, P21CF, P21D0, P21D1, P21D2
- Crankshaft position P0335, P0337, P0338
- Camshaft position P0340, P0342, P0343
- Exhaust camshaft position P0365, P0367, P0368
- EGR P0400, P0401
- Vehicle speed P0500
- Air fuel ratio imbalance P11EA, P11EC, P11ED, P11EE, P11EF, P219A, P219C, P219D, P219E, P219F
Then read the freeze frame for engine state and lean or rich at the moment it set.
- 2
Run the injection mode test.
With coolant at 80 C (176 F) or higher and accessories off, use the active test that forces port injection only, then direct only, and read combined trim on each. Normal is minus 19 to plus 19 percent.
- If both sides are normal, ask whether the car ever ran out of fuel. If so, that is the cause; if not, treat it as intermittent.
- Direct side bad alone means the direct checks, port side bad alone the port checks, and both bad the air and fuel supply checks.
- 3
Direct side checks.
Read high-side fuel pressure with the engine warm. If it is out of range, check direct mode misfire counts: a count in one cylinder means replace that injector; none, or counts across all cylinders, means replace the high-pressure fuel pump assembly. If it is in range, rerun the direct injection test and watch pump duty and combined trim.
- At pump duty between 10 and 50 percent, recheck trim: beyond minus 25 or plus 25 percent, replace a direct injector; inside that, look for an intermittent problem.
- At 50 percent or higher with lean trim (plus 20 or more), replace the high-pressure pump assembly.
- At 50 percent or higher with rich trim (minus 20 or less), or 10 percent or lower with lean trim (plus 20 or more), replace the high-side fuel pressure sensor.
- At 10 percent or lower with rich trim (minus 20 or less), replace the ECM.
- After a pump replacement, clear the codes and run the confirmation drive; if the code returns, replace the ECM.
- 4
Port side checks.
Check port injector volume and injection pattern. Replace any injector that fails; if all check out, replace the ECM.
- 5
Air and fuel supply checks,
in this order:
- Check the PCV hose connections, PCV valve and intake for vacuum leaks; repair or replace.
- Run the air fuel ratio sensor test; the scan tool forces injected volume down and up and sensor current should follow. If it follows, carry on; if not, check the sensor 1 heater, power supply and wiring to the ECM, and replace it if those pass.
- Compare coolant temperature with ambient cold and operating range warm; replace the sensor if it disagrees.
- Run the EGR step position test and watch idle and manifold pressure respond. If not, remove the valve and check that it closes tightly; replace it if not. Return it to step 0 afterward.
- Read mass air flow at 3,000 rpm in park, warm, A/C off. If off specification, skip to the connector check at the end; if in specification, carry on.
- Check low-side fuel pressure. If it is out of specification, check the fuel lines for leaks or blockage; repair them if faulty, or replace the low-pressure fuel pump if fine. If pressure is fine, carry on.
- Check for exhaust gas leaks and repair or replace the part. Inspect the spark plugs, replace one only if it fails, then run a spark test.
- Check the connectors, terminals and wiring between the air flow meter and the ECM and repair any problem, then clear the codes and run the confirmation drive. If the code returns, check the harness, inspect the meter, clear and retest; replace the ECM only if the code is still there.
Get the P0171 lean code tests for your Camry
The fix-first codes, injection mode test, fuel pressure checks and confirmation drive above follow Toyota's own test order. Ask emanuals.ai about your Camry 2.5L and get the exact test steps, specs and relearn procedures from the factory manual.
Specs you need for the Camry P0171 repair
| Air fuel ratio sensor 1 installation torque | 44 N·m (32 ft·lbf) |
|---|
What if the obvious fix does not work?
Check fuel supply before buying sensors or injectors; low fuel pressure can make injector codes appear.
An air leak is the other suspect; a loose or cracked PCV hose or an intake gasket can set the lean code, and a smoke test can find one. Common mistakes are skipping the fix-first codes, swapping sensor 1 before the active test fails it, and skipping the relearn.
If the code returns after a high-pressure pump replacement and the confirmation drive, the next step is the ECM; the same goes for port injectors that check out and for the air flow meter path once the harness and meter are checked and the retest still fails.
How do you confirm the repair?
Run the confirmation drive:
- Clear the codes with the scan tool (even if none are stored), switch the ignition off for at least 30 seconds, then switch it on.
- Warm the engine to 75 C (167 F) coolant or higher with accessories off and idle 2 minutes or more.
- Drive at 60 to 100 km/h (37 to 62 mph) for 5 minutes or more, obeying all traffic laws, then read the pending codes; a pending code means the system is still faulty.
A learning value reset and idle learning are required after replacing the air fuel ratio sensor, air flow meter, injectors, fuel pump, spark plug, ignition coil, EGR valve, coolant temperature sensor or fuel pressure sensor, or repairing an air or exhaust leak, if any of these is true:
- A code was present before the replacement.
- An air fuel ratio learned value was beyond plus or minus 20 percent before it.
- Hard starting, rough idle or stalling occurs afterward.
For idle learning, ignition off 30 seconds, warm to 80 C (176 F) or higher with accessories off, then idle 5 minutes in park; idle speed should read 600 to 700 rpm. After a reset the air fuel learned values should read zero; if not, repeat the reset, and replace the ECM if still not zero.
After replacing the air fuel ratio sensor, inspecting for exhaust leaks at the sensor is required.
Questions mechanics ask about P0171 on the Camry
What else sets with P0171 on the Camry?+–
P0172 is the rich side of the same check, with combined trim at minus 35 percent or lower. P1170 (port) and P117B (direct) are evaluated once a fuel system code has set, and they point at the injection system that was switched off for the test. Any code in the fix-first list stops the lean monitor from running on this Camry, so those get repaired first.
Should I replace the air fuel ratio sensor first on the Camry?+–
No, test it first. The active test forces richer and leaner mixes, and you only go down the sensor path if sensor 1 fails to respond. If it reads lean while the car really is lean, move on to the air leak, coolant temperature, EGR, air flow meter, fuel pressure and exhaust leak checks.
Is there a Toyota record for P0171 on the Camry?+–
Yes. Toyota service bulletin T-SB-0009-23 covers hard start and/or the check engine light with P0171, P0174 or P0087 on certain 2018-2020 Camry models, and it calls for a new fuel pump only when fuel pressure is out of specification. Separately, Toyota ran fuel pump safety recalls (NHTSA 20V-012, 20V-682 and 25V-028) for the low-pressure pump on certain vehicles. The recalls say a failing pump can cause warning lights, rough running or a stall while driving, so check your VIN with Toyota or NHTSA.
Does Toyota cover the low-pressure fuel pump on the Camry?+–
It can. Two Toyota customer support programs cover the low-pressure fuel pump for defects in material or workmanship. Program 23TE04 covers 2018-2020 Camry models whose pump was already replaced under a pump recall or special service campaign, to a fixed end date or 150,000 miles, whichever comes first. Program 23TE05 covers 2019-2020 models not previously in a pump recall or special service campaign, for 15 years from first use regardless of mileage. Both replace the pump once inspection verifies the condition.
Why does P0171 show up after fuel system work on the Camry?+–
The code, or a low rail pressure code, can store while fuel pressure is discharged during the job. Clear the codes afterward, then run the confirmation drive to see whether it returns.
Sources
- Toyota Camry Service & Repair Manual, section Engine Control, SFI System, DTC P017100 System Too Lean Bank 1 (A25A-FKS).OEM Manual
- Toyota service bulletin T-SB-0009-23, "Fuel Pump (Loss of Fuel Pressure)", 2018-2020 Camry, February 9, 2023.Service Bulletin
- Toyota safety recall 20TB02 and 20TA02 (NHTSA 20V-012), "Fuel Pump May Fail", 2018-2019 Camry, January 15, 2020.Recall
- Toyota safety recall 20TA02 (NHTSA 20V-682), "Fuel Pump May Fail", 2018-2020 Camry, November 9, 2020.Recall
- Toyota safety recall 25TA01 (NHTSA 25V-028), "SAFETY RECALL 25TA01 (Remedy Notice)", 2018 Camry, January 22, 2025.Recall
- Toyota customer support program 23TE04, "CUSTOMER SUPPORT PROGRAM 23TE04", 2018-2020 Camry, February 9, 2023.Service Bulletin
- Toyota customer support program 23TE05, "CUSTOMER SUPPORT PROGRAM 23TE05", 2019-2020 Camry, February 9, 2023.Service Bulletin
- emanuals.ai, Query data, "P0171 Toyota Camry".First-Party Data
ASE Master Technician
JC spent 15+ years as a certified Master Mechanic before trading the shop for the keyboard. He's worked across dealerships, owned and operated his own independent garage, and consulted on automotive trade school curricula, reviewing technical textbooks used in vocational programs.
He now serves as Editor-in-Chief at emanuals.ai, where he oversees the platform's technical content. He's one of the few voices in automotive publishing who turned wrenches professionally for decades before he had a byline.
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