DTC P0171

BHE010200100W20

DTC P0171

System too lean

DETECTION CONDITION

• The PCM monitors the short term fuel trim (SHRTFT) and long term fuel trim (LONGFT) when under closed loop fuel control. If the fuel trim is more than the specification, the PCM determines that the system is too lean.

Diagnostic support note

• This is a continuous monitor (Fuel system).
• The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
• PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
• FREEZE FRAME DATA is available.
• The DTC is stored in the PCM memory.

POSSIBLE CAUSE

• Front HO2S malfunction
• Excess air suction in intake-air system
• Leakage exhaust gas
• MAF sensor malfunction
• Fuel line pressure malfunction
• Fuel pump unit malfunction
• Leakage fuel
• Ignition system malfunction
– High-tension lead malfunction
– Incorrect power supply to ignition coil
– Ignition coil malfunction
• Insufficient compression
– Metering oil pump malfunction
– Engine oil condition malfunction
– Rised oil pressure
– Oil passage malfunction
– Engine malfunction
• Fuel injector malfunction
• PCM malfunction

Diagnostic procedure

STEP

INSPECTION

ACTION

1

VERIFY FREEZE FRAME DATA HAS BEEN RECORDED

• Has FREEZE FRAME DATA been recorded?
Yes
Go to the next step.
No
Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2

VERIFY RELATED REPAIR INFORMATION AVAILABILITY

• Verify related service repair information availability.
• Is any related repair information available?
Yes
Perform repair or diagnosis according to the available repair information.
• If the vehicle is not repaired, go to the next step.
No
Go to the next step.
3

VERIFY RELATED PENDING CODE OR STORED DTC

• Turn the ignition switch off, then to the ON position (Engine off).
• Verify the related PENDING CODE or stored DTCs.
• Are other DTCs present?
Yes
• If misfire DTC is present, go to Step 8.
• If other DTC is present, go to the appropriate DTC inspection.
(See DTC TABLE.)
No
• If drive ability concern is present, go to Step 8.
• If other, go to the next step.
4

IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA

• Is DTC P0171 on FREEZE FRAME DATA?
Yes
Go to the next step.
No
Go to the FREEZE FRAME DATA DTC inspection.
(See DTC TABLE.)
5

VERIFY CURRENT INPUT SIGNAL STATUS

• Connect the WDS or equivalent to the DLC-2.
• Verify the following PIDs.
– APP
– ECT
– MAF
– TP
– VSS
• Are the PIDs normal?
Yes
Go to the next step.
No
Inspect the malfunctioning part according to the inspection results.
Then go to Step 24.
6

VERIFY CURRENT INPUT SIGNAL STATUS UNDER FREEZE FRAME DATA CONDITION

• Connect the WDS or equivalent to the DLC-2.
• Verify the following PIDs under the FREEZE FRAME DATA condition.
– APP
– ECT
– MAF
– TP
– VSS
• Are the PIDs normal?
Yes
Go to the next step.
No
Inspect the malfunctioning part according to the inspection results.
Then go to Step 24.
7

VERIFY CURRENT INPUT SIGNAL STATUS OF FRONT HO2S

• Connect the WDS or equivalent to the DLC-2.
• Start the engine and warm it up completely.
• Access the O2S11 PID.
• Read the O2S11 PID under following accelerator pedal condition (in PARK or NEUTRAL).
– Less than 1 mA when accelerator pedal is suddenly depressed (rich condition).
– More than 1 mA just after release of accelerator pedal (lean condition)
• Is the PID normal?
Yes
Inspect for air suction at followings due to cracks, damages and loosening parts:
• From air cleaner to throttle body
• From throttle body to intake manifold
• Vacuum hoses
Note
• Engine speed may change when rust penetrating agent (cab cleaner etc.) is sprayed on the air suction area.
Repair or replace the malfunctioning part, then go to Step 24.
No
Go to the next step.
8

INSPECT EXHAUST SYSTEM FOR EXHAUST GAS LEAKAGE

• Visually inspect exhaust gas leakage in the exhaust system.
• Is there exhaust gas leakage?
Yes
Repair or replace the malfunctioning part, then go to Step 24.
No
Replace the front HO2S, then go to Step 24.
9

VERIFY CURRENT INPUT SIGNAL STATUS OF MAF SENSOR

• Connect the WDS or equivalent to the DLC-2.
• Start the engine.
• Access the MAF PID.
• Verify that the MAF PID changes quickly according to race the engine RPM.
• Is the PID normal?
Yes
Go to the next step.
No
Replace the MAF/IAT sensor, then go to Step 24.
10

INSPECT INTAKE-AIR SYSTEM FOR EXCESSIVE AIR SUCTION

• Visually inspect for loosen, cracks or damages hoses in intake-air system.
• Is there any malfunction?
Yes
Repair or replace the malfunctioning part, then go to Step 24.
No
Go to the next step.
11

INSPECT FUEL LINE PRESSURE

• Perform the "FUEL LINE PRESSURE INSPECTION".
• Is there any malfunction?
Yes
• If the fuel line pressure is too low, go to the next step.
• If the fuel line pressure is too high, replace the fuel pump unit, then go to Step 24.
No
Go to Step 13.
12

INSPECT FUEL SYSTEM FOR FUEL LEAKAGE

• Visually inspect fuel leakage in the fuel system.
• Is there fuel leakage?
Yes
Repair or replace the malfunctioning part, then go to Step 24.
No
Replace the fuel pump unit, then go to Step 25.
13

INSPECT IGNITION COIL OPERATION AND HIGH-TENSION LEAD WITH TIMING LIGHT

• Inspect the blinking condition on each high-tension lead using timing light at idle.
• Do all the high-tension leads show blinking condition?
Yes
Go to Step 17.
No
Go to the next step.
14

INSPECT HIGH-TENSION LEAD OF NO BLINKING HIGH-TENSION LEAD

• Inspect the high-tension leads.
• Is there any malfunction?
Yes
Replace the malfunctioning high-tension lead, then go to Step 24.
No
Go to the next step.
15

INSPECT IGNITION COIL POWER CIRCUIT FOR OPEN CIRCUIT OR SHORT TO GND

• Turn the ignition switch to the ON position (Engine off).
• Measure the voltage between ignition coil terminal C (wiring harness-side) and body GND.
• Is the voltage B+?
Yes
Go to the next step.
No
Repair or replace the wiring harness for a possible open circuit or short to GND, then go to Step 24.
16

INSPECT IGNITION COIL

• Inspect the ignition coil.
• Is there any malfunction?
Yes
Replace the ignition coil, then go to Step 24.
No
Go to the next step.
17

INSPECT AIR SYSTEM OPERATION

• Perform the "AIR System Inspection".
• Does AIR system operate properly?
Yes
Go to the next step.
No
Repair or replace malfunctioning part according to the inspection results.
Then go to Step 23.
18

INSPECT ENGINE COMPRESSION

• Inspect the engine compression.
• Is there any malfunction?
Yes
Go to the next step.
No
Go to Step 23.
19

INSPECT METERING OIL PUMP

• Inspect the metering oil pump.
• Is there any malfunction?
Yes
Repair or replace the malfunctioning part according to the inspection results.
Overhaul or replace the engine.
Then go to Step 24.
No
Go to the next step.
20

INSPECT ENGINE OIL CONDITION

• Inspect the engine oil condition.
• Is the engine oil condition normal?
Yes
Go to the next step.
No
Replace the engine oil.
Inspect the ECT sensor and related harnesses.
Overhaul or replace the engine.
Then go to Step 24.
21

INSPECT OIL PRESSURE

• Inspect the oil pressure.
• Is there any malfunction?
Yes
Repair or replace the malfunctioning part according to the inspection results.
Overhaul or replace the engine.
Then go to Step 24.
No
Go to the next step.
22

INSPECT OIL PASSAGE

• Inspect the oil pipe between metering oil pump and metering oil nozzle.
• Is there any malfunction?
Yes
Inspect and repair for leakage and/or clogged in oil passage at engine.
Overhaul or replace the engine.
Then go to Step 24.
No
Overhaul or replace the engine.
Then go to the next step.
23

INSPECT FUEL INJECTOR

• Inspect the fuel injector.
• Is there any malfunction?
Yes
Replace the fuel injector, then go to the next step.
No
Go to the next step.
24

VERIFY TROUBLESHOOTING OF DTC P0171 COMPLETED

• Make sure to reconnect all disconnected connectors.
• Clear the DTC from the PCM memory using the WDS or equivalent.
• Perform the "DRIVE MODE 1".
• Is the PENDING CODE same as the DTC present?
Yes
Replace the PCM, then go to the next step.
No
Go to the next step.
25

VERIFY AFTER REPAIR PROCEDURE

• Perform the "AFTER REPAIR PROCEDURE".
• Are any DTCs present?
Yes
Go to the applicable DTC inspection.
(See DTC TABLE.)
No
DTC troubleshooting completed.