DTC P0171, P0174 [AJ]

BME010200100221

DTC P0171

DTC P0174

Fuel trim system (RH) too lean

Fuel trim system (LH) too lean

DETECTION CONDITION

• PCM monitors short term fuel trim (SHRTFT) and long term fuel trim (LONGFT) values when closed loop fuel control. If fuel trim exceeds preprogrammed criteria, PCM determines that the fuel system is too lean.
Diagnostic support note
• This is a continuous monitor. (FUEL SYSTEM)
• MIL illuminates if PCM detects the above malfunction conditions in two consecutive drive cycles.
• PENDING CODE is available if PCM detects the above malfunction conditions during first drive cycle.
• FREEZE FRAME DATA is available.
• DTC is stored in the PCM memory.

POSSIBLE CAUSE

• Misfire
• Front HO2S deterioration
• Front HO2S heater malfunction
• Pressure regulator malfunction
• Fuel pump malfunction
• Fuel filter clogged or restricted
• Fuel leakage on fuel line from fuel delivery pipe and fuel pump
• Fuel return hose clogged
• Leakage exhaust system
• Purge solenoid valve malfunction
• Purge solenoid hoses improper connection
• Insufficient compression

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 FREEZE FRAME DATA on repair order, then go to the next step.
2
VERIFY RELATED SERVICE INFORMATION AVAILABILITY
• Check for related Service Information availability.
• Is any related Service Information available?
Yes
Perform repair or diagnosis according to available Service Information.
• If vehicle is not repaired, go to the next step.
No
Go to the next step.
3
VERIFY RELATED PENDING CODE OR STORED DTCS
• Turn the ignition switch off, then to the ON position (Engine off).
• Verify related PENDING CODE or stored DTCs.
• Is other DTCs present?
Yes
If misfire DTC is present, go to step 8.
If other DTC is present, go to appropriate DTC troubleshooting procedures.
No
If drive ability concern is present, go to Step 8.
If not, go to the next step.
4
IDENTIFY TRIGGER DTC FOR FREEZE FRAME DATA
• Is DTC P0171or P0174 on FREEZE FRAME DATA?
Yes
Go to the next step.
No
Go to troubleshooting procedures for DTC on FREEZE FRAME DATA.
5
VERIFY CURRENT INPUT SIGNAL STATUS (IGNITION SWITCH TO ON/IDLE)
• Access ECT, MAF, TP and VSS PIDs using WDS or equivalent.
• Is there any signal that is far out of specification when the ignition switch is at the ON position and engine runs?
Yes
Inspect the sensor and excessive resistance in related wiring harnesses. Repair or replace if necessary. Then go to Step 18.
No
Go to the next step.
6
VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION
• Inspect same PIDs as Step 5 while simulating FREEZE FRAME DATA condition.
• Is there any input signal which causes drastic changes?
Yes
Inspect the sensor and related wiring harnesses, and repair or replace it. Then go to Step 18.
No
Go to the next step.
7
VERIFY CURRENT INPUT SIGNAL STATUS OF FRONT HO2S (RH, LH)
• Access O2S11 for P0171 or O2S21 for P0174 PID using WDS or equivalent.
• Check PID under following accelerator pedal condition (in PARK).
• Is PID reading normal?

- Above 0.45 V when suddenly depress accelerator pedal (rich condition).

- Below 0.45 V just after release of accelerator pedal (lean condition)

Yes
Inspect for air suction at followings due to cracks, damages and loosening parts:
• From air cleaner to throttle body
• From throttle body to dynamic chamber
• From dynamic chamber to intake manifold
• Vacuum hoses
Note
• Engine speed may change when rust penetrating agent is sprayed on the air suction area.
Repair or replace the malfunctioning part, then go to Step 18.
No
Visually inspect for any gas leakage between exhaust manifold and front HO2S.
• If there is no leakage, replace the FRONT HO2S.
Then go to Step 18.
8
INSPECT MAF PID
• Start the engine.
• Access MAF PID using WDS or equivalent.
• Verify that MAF PID changes quickly according to race engine RPM.
• Is MAF PID response normal?
Yes
Go to the next step.
No
Replace the MAF sensor, then go to Step 18.
9
INSPECT FOR EXCESSIVE AIR SUCTION OF INTAKE AIR SYSTEM
• Visually inspect for loosen, cracks or damages hoses on intake air system.
• Is there any malfunction?
Yes
Repair or replace source of air suction, then go to Step 18.
No
Go to the next step.
10
INSPECT FUEL LINE PRESSURE
• Turn the ignition switch off.
Note
• If engine won't start, inspect fuel line pressure with key ON.
• Inspect fuel line pressure while engine running.
• Is fuel line pressure normal?
Yes
Go to step 13.
No
• If fuel line pressure is excess high: Inspect fuel pump maximum pressure and Fuel return line for clogged.
- If any problem is found, repair or replace suspected parts.
- If all items above are normal, replace pressure regulator.
Then go to Step 18.
• If fuel line pressure is too low: Go to the next step.
11
INSPECT FUEL PUMP MAXIMUM PRESSURE
• Perform fuel pump maximum pressure test.
• Is fuel pump maximum pressure normal?
Yes
Go to the next step.
No
Inspect fuel pump circuit for open or poor connection.
Repair or replace suspected circuit, then go to Step 18.
• If circuit is normal, replace the fuel pump. Then go to Step 18.
12
INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE
• Visually inspect fuel line for any leakage.
• Is any fuel leakage found?
Yes
Replace suspected fuel line, then go to Step 18.
No
Inspect fuel filters for the following:
• Restriction or clogging at the fuel filter (high-pressure side).
• Foreign materials or stain inside the fuel filter (low-pressure side)
Perform the following actions as result.
• If restriction or clogging is found at the fuel filter (high-pressure side), replace the fuel filter.
• If foreign materials or stain is found inside the fuel filter (low-pressure side), clean off the fuel tank and filter.
• If all items above are normal, replace the pressure regulator.
Then go to Step 18.
13
INSPECT FUEL INJECTOR OPERATION
• Remove fuel injector from suspected bank.
• Swap the fuel injector with injector on other bank.
• Start the engine.
• Is fuel trim system lean DTC for bank which has a malfunctioning fuel injector?
Yes
Replace the fuel injector, then go to Step 18.
No
Go to the next step.
14
CHECK IGNITION COIL OPERATION
• Perform spark test.
(See Spark Test)
• Do all cylinders show blinking condition?
Yes
Go to step 17.
No
Go to the next step.
15
INSPECT POWER SUPPLY TERMINAL AT IGNITION COIL CONNECTOR
• Disconnect ignition coil connector.
• Turn the ignition switch to the ON position (Engine off).
• Measure the voltage at ignition coil connector terminal D (wiring harness-side) and body ground.
• Is the voltage B+?
Yes
Go to the next step.
No
Inspect for open circuit between ignition coil connector and ignition switch. Repair or replace the wiring harness, then go to Step 18.
16
INSPECT IGNITION COIL RESISTANCE
• Inspect ignition coil resistance.
• Is coil resistance normal?
Yes
Go to the next step.
No
Replace the ignition coil, then go to Step 18.
17
INSPECT ENGINE COMPRESSION
• Inspect engine compression.
• Is it normal?
Yes
Go to the next step.
No
Implement engine overhaul for repairs, then go to the next step.
18
VERIFY TROUBLESHOOTING OF DTC P0171 or P0174 COMPLETED
• Make sure to reconnect all disconnected connectors.
• Clear the DTC from the PCM memory using the WDS or equivalent.
• Run PCM adaptive memory procedure drive mode and HO2S heater, HO2S, and TWC repair verification drive mode. (European (L.H.D.) specs.)
• Run PCM adaptive memory procedure drive mode and HO2S heater, HO2S, and EGR system repair verification drive mode. (Australian, General (L.H.D. R.H.D.) specs.)
• Stop the vehicle and access PID/DATA MONITOR RECORDED to inspect DRIVE MODE completion status.
•  Verify RFCFLAG changes to OFF for FUEL SYSTEM MONITOR. If not, run DRIVE MODE again.
• Access PENDING CODE.
• Is the PENDING CODE of same DTC present?
Yes
Replace the PCM, then go to the next step.
No
Go to the next step.
19
VERIFY AFTER REPAIR PROCEDURE
• Perform "After Repair Procedure".
• Is there any DTC present?
Yes
Go to the applicable DTC inspection.
No
Troubleshooting completed.