indicated, go to the indicated DTC's troubleshooting.
FAILED : Go to step 1 and recheck. If the PCM was updated, substitute a known-good PCM See PCM
UPDATE or PCM REMOVAL AND INSTALLATION , then check the OBD STATUS again.
NOT COMPLETED : Meet the test condition, and check the OBD STATUS again.
DTC P0171: FUEL SYSTEM TOO LEAN
Fig. 79: DTC Troubleshooting Flow Chart (P0171)
Courtesy of AMERICAN HONDA MOTOR CO., INC.
NOTE:
ο¬
Before you troubleshoot, record all freeze data and any on-board
snapshot, and review the general troubleshooting information See HOW
TO TROUBLESHOOT THE A/T SYSTEM or HOW TO TROUBLESHOOT THE
FUEL AND EMISSIONS SYSTEMS .
ο¬
Do not clear the DTC or reset the PCM before beginning this
troubleshooting procedure until instructed to clear it. Clearing the DTC or
resetting the PCM can delete valuable diagnostic information, even if the
on-board snapshot and the freeze data is saved.
ο¬
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Inspect for aftermarket fuel system and engine components before
beginning troubleshooting.
If any of the DTCs listed below are stored at the same time as DTC P0171,
troubleshoot those DTCs first, then recheck for P0171.
P0101, P0102, P0103: MAF sensor
P0106, P0107, P0108: MAP sensor
P0133, P1172, P1157, P2238, P2252, P2A00: A/F sensor (Sensor 1)
P0134, P0135: A/F sensor (Sensor 1) heater
P0137, P0138, P0139, P2270: Secondary HO2S (Sensor 2)
P0201, P0202, P0203, P0204: Fuel injector
P0141: Secondary HO2S (Sensor 2) heater
P0443, P0496: EVAP canister purge valve
P2646, P2647, P2648, P2649: VTEC system
DTC Description
Confirmed DTC
Pending DTC
Freeze Frame
P0171 FUEL SYSTEM TOO LEAN
1. Problem verification-Idle:
ο‘
1. Start the engine, and let it idle without load (in P or N).
2. Check the parameter(s) below with the HDS.
ο‘
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold?
YES : The AF FB (ST FUEL TRIM) is too high at idle. Go to step 3.
NO : The AF FB (ST FUEL TRIM) is OK at idle. Go to step 2.
2. Problem verification-On-board Snapshot:
ο‘
1. Review the on-board snapshot and record the value of the parameters below when AF FB (ST
FUEL TRIM) was at its highest point.
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
ο‘
2. Drive the vehicle according to the conditions determined above.
Current conditions
Signal
Values
Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
ο‘
3. Check the parameter(s) below with the HDS while driving.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold under the on-board snapshot conditions?
YES : AF FB (ST FUEL TRIM) is too high under the conditions above. Go to step 3.
NO : AF FB (ST FUEL TRIM) is OK under the same conditions as the on-board snapshot. The system is
normal at this time.
3. Check for MAF Sensor Debris:
ο‘
1. REMOVE THE MAF SENSOR/IAT SENSOR .
ο‘
2. Check for lint, bugs, and other foreign objects in the sensor.
Is there debris in the MAF sensor?
YES : Remove the debris from the MAF sensor and then use a vacuum cleaner to remove any debris from
the air cleaner housing, then do the repair verification .
NO : Reinstall the MAF sensor/IAT sensor. Go to step 4.
4. Check for Disconnected or Damaged Components:
1. Visually inspect each of the components below for disconnected hoses, cracks, or damage:
ο‘
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Crankcase breather hose (A)
Air cleaner housing (B)
Oil cap (C) and dipstick (D)
Fig. 80: Identifying Breather Hose, Air Cleaner Housing, Oil Cap And Dipstick
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Are any components disconnected or damaged?
YES : Repair as necessary, then do the repair verification .
NO : Go to step 5.
5. Check Brake Booster:
ο‘
1. Continue to let the engine idle.
ο‘
2. Pinch the brake booster vacuum hose (A) connecting to the intake manifold.
Fig. 81: Identifying Brake Booster Vacuum Hose
Courtesy of AMERICAN HONDA MOTOR CO., INC.
ο‘
3. Check the parameter(s) below with the HDS with the vacuum hose pinched.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold?
YES : The brake booster is not leaking. Go to step 6.
NO : There is a leak in the brake booster or hoses. Check the brake booster vacuum hoses for leaks. If no
leaks are found, replace the brake booster, then do the repair verification .
6. Check PCV System:
ο‘
1. Continue to let the engine idle.
2. Pinch the PCV vacuum hose (A).
ο‘
Fig. 82: Identifying PCV Vacuum Hose
Courtesy of AMERICAN HONDA MOTOR CO., INC.
ο‘
3. Check the parameter(s) below with the HDS with the vacuum hose pinched.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold?
YES : The PCV system is not leaking. Go to step 7.
NO : There is a leak in the PCV system. Check the vacuum hoses for leaks and repair as needed, then do
the repair verification .
7. Check MAF Sensor Reading:
ο‘
1. Start the engine and hold the engine speed at 3, 000 rpm until the radiator fan comes on.
2. Make sure the following conditions are met:
ο‘
ο¬
ο¬
ο¬
ECT Sensor 1 above 158 Β°F (70 Β°C)
Transmission in P or N
All engine and electrical loads turned off
Current conditions
Signal
Values
Unit
ECT SENSOR 1
ο‘
3. Monitor the ENGINE SPEED in the DATA LIST with the HDS, then hold the engine speed at 2,
500 rpm with the accelerator pedal held steady.
Current conditions
Signal
Values
Unit
ENGINE SPEED
ο‘
4. Check the parameter(s) below with the HDS at 2, 500 rpm.
Threshold Current conditions
Signal
Values Unit Values
Unit
MAF SENSOR 7.0-8.6 g/s
Do the current condition(s) match the threshold?
YES : The MAF sensor is OK. Go to step 8.
NO : The MAF sensor is reading incorrectly. Inspect for a cracked, damaged, or incorrectly installed air
cleaner assembly. If OK, REPLACE THE MAF SENSOR/IAT SENSOR , then do the repair
verification .
8. Check Fuel Pressure:
ο‘
1. Check the fuel pressure under the conditions when AF FB (ST FUEL TRIM) is 1.33 or more.
Current conditions
Signal
Values
Unit
AF FB (ST FUEL TRIM)
2
Is the fuel pressure between 330-380 kPa (3.4-3.9 kgf/cm , 48-55 psi)?
YES : The fuel pressure is OK. Go to step 9.
NO : Replace the fuel tank unit See FUEL TANK UNIT DISASSEMBLY AND REASSEMBLY or
FUEL TANK UNIT REMOVAL AND INSTALLATION , then do the repair verification .
9. Check for Intake Manifold Vacuum Leaks:
ο‘
1. Disconnect the intake air duct from the air cleaner housing.
ο‘
2. Connect a large intake manifold adaptor cone into the intake air duct from the OTC LeakMaster
evaporative emissions system tester kit.
ο‘
3. Use the OTC LeakMaster evaporative emissions system tester to direct smoke into the intake
manifold.
ο‘
4. Inspect each of the areas below for signs of leaks:
ο¬
ο¬
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Intake manifold and gaskets
Throttle body and gasket
Air intake ducting
All vacuum and air hoses
Are there any leaks?
YES : Repair the vacuum leak, then do the repair verification .
NO : Reconnect any disconnected components, then go to step 10.
10. Replace Fuel Injectors:
ο‘
1. REPLACE THE FUEL INJECTORS WITH KNOWN-GOOD INJECTORS .
ο‘
2. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.33 or
more.
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
Current conditions
Signal
Values
Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
ο‘
3. Check the parameter(s) below with the HDS while driving.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold under the on-board snapshot conditions?
YES : The fuel injectors are not the cause of the high AF FB (ST FUEL TRIM) value. Go to step 11.
NO : The fuel injectors were causing the high AF FB (ST FUEL TRIM) value. REPLACE THE
ORIGINAL INJECTORS , then do the repair verification .
11. Replace A/F Sensor (Sensor 1)
ο‘
ο‘
1. REPLACE THE A/F SENSOR (SENSOR 1) WITH A KNOWN-GOOD SENSOR .
2. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.33 or
more.
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
Current conditions
Signal
Values
Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
ο‘
3. Check the parameter(s) below with the HDS while driving.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold under the on-board snapshot conditions?
YES : The A/F sensor (Sensor 1) is not the cause of the high AF FB (ST FUEL TRIM) value. Go to step
12.
NO : The A/F sensor (Sensor 1) was causing the high AF FB (ST FUEL TRIM) value. REPLACE THE
ORIGINAL A/F SENSOR (SENSOR 1) , then do the repair verification .
12. Replace Fuel:
NOTE:
There is an increased likelihood of a fuel related issue if the misfire
appeared shortly after refueling. The MIL DIST (MIL Distance) value in the
DATA LIST in combination with the fuel level may help you make this
determination.
ο‘
ο‘
1. Remove the fuel tank unit and then drain and refill the fuel tank with known-good fuel.
2. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.33 or
more.
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
Current conditions
Values Unit
Signal
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
ο‘
3. Check the parameter(s) below with the HDS while driving.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold under the on-board snapshot conditions?
YES : The fuel is not the cause of the high AF FB (ST FUEL TRIM) value. Substitute a known-good
PCM See PCM REMOVAL AND INSTALLATION or PCM UPDATE , then do the repair
verification .
NO : The fuel was causing the high AF FB (ST FUEL TRIM) value. do the repair verification .
REPAIR VERIFICAITON
ο‘
ο‘
1. Turn the ignition switch to ON (II).
2. Reset the PCM with the HDS See HOW TO TROUBLESHOOT THE A/T SYSTEM or HOW
TO TROUBLESHOOT THE FUEL AND EMISSIONS SYSTEMS .
ο‘
ο‘
3. DO THE PCM IDLE LEARN PROCEDURE .
4. Start the engine. Hold the engine speed at 3, 000 rpm without load (in P or N) until the radiator fan
comes on, then let it idle.
ο‘
5. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 1.33 or more.
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
Current conditions
Signal
Values
Unit
ENGINE SPEED
VEHICLE SPEED
REL TP SENSOR
APP SENSOR
ο‘
6. Check the parameter(s) below with the HDS while driving.
Threshold
Values
Current conditions
Unit Values Unit
Signal
AF FB (ST FUEL TRIM) More than 1.33
Do the current condition(s) match the threshold under the on-board snapshot conditions?
YES : AF FB (ST FUEL TRIM) is too high. Go to step 3.
NO : AF FB (ST FUEL TRIM) is OK. Troubleshooting is complete.
DTC P0172: FUEL SYSTEM TOO RICH
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