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Adaptive Fuel Control

DTC DETECTION CONDITION POSSIBLE COUSES CHART

DTC P0171, P0172, P0174, P0175 ADAPTIVE FUEL CONTROL
DETECTION CONDITION
  • P0171 indicates the fuel/air ratio is too lean (Bank 1).
  • P0172 indicates the fuel/air ratio is too rich (Bank 1).
  • P0174 indicates the fuel/air ratio is too lean (Bank 2).
  • P0175 indicates the fuel/air ratio is too rich (Bank 2).
POSSIBLE CAUSES
  • DTC P0171 and DTC P0174
    • Ethanol content in the fuel
    • Fuel filter plugged or dirty
    • Fuel pump weak or leaking
    • Leaking fuel injector(s)
    • Low fuel pressure or running out of fuel
    • EVAP vapor management valve leaking
    • Fuel supply line restricted
    • Air leaks after the MAF/IAT
    • Vacuum leaks (vacuum lines and gaskets)
    • Stuck EGR valve
    • Cam timing
    • Cylinder compression
    • Exhaust leaks before or near the HO2S(s)
  • DTC P0172 and DTC P0175
  • Excessive fuel pressure
  • PCV system
  • Incorrectly seated engine oil dipstick
  • Vacuum leaks (vacuum lines and gaskets)
  • Stuck EGR valve
  • Oil overfill
  • Cam timing
  • Cylinder compression
HINT Fuel System Monitor 
  • The fuel control system uses fuel trim tables stored in the PCM to compensate for variability in fuel system components due to normal wear and aging.
  • The fuel trim strategy learns deviations during closed-loop engine operation.
  • The fuel trim has 2 means of adapting; a long term fuel trim and a short term fuel trim system.
  • Inputs from ECT/CHT, IAT, MAP, and MAF/IAT sensors are required to activate the fuel trim system.
  • The HO2S detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air/fuel ratio.
  • A fuel trim factor is added to the fuel injector pulse width calculation according to the long and short term fuel trims.
  • The long term trim values at their rich or lean limits indicate a fuel system malfunction.
DTC DETECTION CONDITION POSSIBLE COUSES CHART

STEP INSPECTION ACTION
1 PCM QUICK TEST
  • Was PCM Quick Test carried out? 
 Yes GO to the next step.
No CARRY OUT the PCM Quick Test. See PCM QUICK TEST  .
2 CARRY OUT KOER SELF-TEST
  • Disconnect the fuel vapor hose from the intake manifold and plug fitting at the intake manifold.
  • Start engine and run at 2,000 RPM for 5 minutes, then return to idle.
  • Carry out Key ON, Engine Running (KOER) self-test.
  • Check self-test DTCs.
  • Is DTCs P0040, P0041, P0021, P1127, or P0402 present? 
 Yes Key OFF.
Disregard current DTCs at this time. See DTC INDEX - PCM  to continue diagnosis of other DTCs.
No Key OFF.
GO to the next step.
3 DETERMINE DTC BEING DIAGNOSED
  • Check self-test DTCs.
  • Is DTC P0171 or P0174 present? 
 Yes Key OFF.
GO to step 5.
No GO to the next step.
4 DETERMINE DTC BEING DIAGNOSED
  • Check self-test DTCs.
  • Is DTC P0172 or P0175 present? 
 Yes GO to step 9.
No See TEST 3: INTERMITTENT  .
5 CARRY OUT A VISUAL INSPECTION ON THE INTAKE AIR SYSTEM AND ALL VACUUM HOSES
  • Key OFF.
  • Check the intake air system for leaks, obstructions, and damage.
  • Inspect the entire length of all the vacuum hoses for:
    • correct connections
    • damage or cracks
    • damaged or cracked vacuum tees
  • Verify the integrity of the positive crankcase ventilation (PCV) system.
  • Verify the correct PCV valve part number.
  • Is the concern present? 
 Yes GO to step 7.
No GO to the next step.
6 CHECK FOR THE PRESENCE OF A VACUUM LEAK
NOTE:
  • Fuel trim values at idle are more sensitive to a vacuum leak. The vacuum leak (unmetered air) represents a large portion of the total air flow at idle than at part throttle.
  • The barometric pressure (BARO) PID is not a recommended PID to monitor when diagnosing a vacuum leak. Barometric pressure is calculated during high engine load, when the vacuum leak represents a small portion of the total air flow. When calculating the total fuel correction in the following steps, if LONGFT1 equals +13% and SHRTFT1 equals +23%, the total fuel correction for bank 1 equals +36%. If LONGFT2 equals +24% and SHRFT2 equals -3% the total fuel correction for bank 2 equals +21%. If the freeze frame ECT PID is available, stabilize the engine at the temperature recorded by the freeze frame ECT PID. If the freeze frame ECT PID is not available, maintain the engine coolant temperature between 82 - 101°C (180 - 215°F) and the intake air temperature less than 46°C (115°F).
  • Key ON, engine running (KOER).
  • Access the PCM and monitor the ECT, CHT and IAT PIDs.
  • Access the PCM and monitor the LONGFT1, SHRFT1, LONGFT2 and SHRTFT2 PIDs.
  • Allow the engine to stabilize at the temperature necessary to recreate the concern.
  • Mathematically add and record the LONGFT PID value to the SHRTFT PID value for each bank, for a total fuel correction at idle.
  • Increase the engine speed to 3,500 RPM for 10 seconds. For vehicles with electronic throttle control (ETC), increase the engine speed to the maximum RPM without activating RPM limiting. Record the LONGFT1, SHRTFT1, LONGFT2, and SHRTFT2 PID values.
  • Mathematically add and record the LONGFT PID value to the SHRTFT PID value for each bank, for a total fuel correction at 3,500 RPM or the maximum allowable RPM for vehicles with ETC.
  • Is the total fuel correction value difference, between idle and 3,500 RPM or the maximum allowable RPM for vehicles with ETC, less than 15 percent? 
 Yes No vacuum leak is present. GO to step 11.
No GO to the next step.
7 LOCATE THE VACUUM LEAK
CAUTION:
  • Do not clamp or pinch a hard plastic hose. Use a vacuum cap or equivalent to restrict the hose.
NOTE:
  • Restricting the EVAP vapor hose while the EVAP emission canister is purging may shift the SHRTFT. Carry out a visual inspection as necessary.
NOTE:
  • When monitoring for a decrease in the SHRTFT PIDs in the following steps, if SHRTFT1 equals +15% and the hose is restricted, SHRTFT 1 decreases to -7%. The total decrease in the SHRTFT PIDs equals 22%.
  • Locate the vacuum tees for the intake air and PCV systems.
  • Access the PCM and monitor the SHRTFT1 and SHRTFT2 PIDs.
  • Restrict the vacuum lines one at a time for 30 seconds. If a vacuum leak is present, the SHRTFT PID values decrease as the hose is restricted.
  • Is the decrease in the SHRTFT PIDs greater than 15% when one of the vacuum hoses is restricted? 
 Yes GO to the next step.
No INSPECT the intake air system for a vacuum leak in the intake manifold or intake gaskets. REPAIR as necessary. GO to the next step.
8 VACUUM LEAK REPAIR VERIFICATION
NOTE:
  • If the freeze frame ECT PID is available, stabilize the engine at the temperature recorded by the freeze frame ECT PID. If the freeze frame ECT PID is not available, maintain the engine coolant temperature between 82 - 101°C (180 - 215°F) and the intake air temperature less than 46°C (115°F).
  • Access the PCM and monitor the SHRTFT1 and SHRTFT2 PIDs.
  • Allow the engine to stabilize at the temperature necessary to recreate the concern.
  • Record the SHRTFT1 and SHRTFT2 PID values.
  • Key OFF.
  • Repair the vacuum leak.
  • Key ON, engine running (KOER).
  • Allow the engine to stabilize at the temperature necessary to recreate the concern.
  • Access the PCM and monitor the SHRTFT1 and SHRTFT2 PIDs.
  • Compare the recorded SHRTFT PID values, prior to the vacuum leak repair, to the current SHRTFT PID values.
  • Is the decrease in the SHRTFT PIDs greater than 15%? 
 Yes RESET the keep alive memory (KAM).
See ELECTRONIC ENGINE CONTROL (EEC) SYSTEM  .
GO to step 29.
No A vacuum leak is still present.
GO to step 7.
9 DTCs P0172 or P0175: RICH SYSTEM DTCs
NOTE:
  • Do not clear the DTCs or reset the keep alive memory (KAM).
  • Access the PCM and record the freeze frame data.
  • Retrieve and record the self-test DTCs.
  • Are any DTCs present other than the following: P0172 or P0175? 
 Yes DISREGARD the current DTC at this time.
DIAGNOSE the next DTC. See DTC INDEX - PCM  .
GO to step 29.
No GO to the next step.
10 INSPECT THE ENTIRE INTAKE AIR SYSTEM FOR DEBRIS, BLOCKAGE OR OTHER DAMAGE
  • Check the intake air system for obstructions, restrictions and damage.
  • Check the throttle plate for obstructions or sludge.
  • Check the air filter element and housing for blockage.
  • Access the PCM-HO2S Signal PID using an IDS or equivalent tester.
  • Is a concern present? 
 Yes REPAIR as necessary. CLEAR the DTCs.
REPEAT the self-test.
GO to step 29.
No GO to step 17.
11 CHECK HO2S CIRCUIT(S) FOR OPEN IN HARNESS
  • Disconnect the suspected HO2S sensor.
  • Disconnect: PCM.
  • Measure the resistance between PCM pin E8 or PCM pin E9 and suspect HO2S sensor connector pin 4, harness side.
  • Is the resistance less than 5 ohms? 
 Yes REPAIR the open circuit.
GO to step 29.
No GO to the next step.
12 CHECK HO2S SIGNAL CIRCUIT FOR SHORT TO SIGTRN IN HARNESS
  • Measure the resistance between PCM pin E8 or PCM pin E9 and PCM pin E49.
  • Is the resistance greater than 10K ohms? 
 Yes GO to the next step.
No REPAIR the short circuit.
GO to step 29.
13 CHECK HO2S SIGNAL CIRCUIT FOR SHORT TO GROUND IN HARNESS
  • Measure the resistance between PCM pin E8 or PCM pin E9 and ground.
  • Is the resistance greater than 10K ohms? 
 Yes GO to the next step.
No REPAIR the short circuit.
GO to step 19.
14 HO2S CIRCUIT TEST (WITH LEAN DTCs)
  • PCM connector connected.
  • Connect a 5 amp fused jumper wire between HO2S signal and VPWR.
  • Key ON, Engine Off (KOEO).
  • Access the PCM and monitor the HO2S signal PID using IDS or equivalent tester.
  • Is the voltage greater than 1.3 volts? 
 Yes GO to step 19.
No GO to the next step.
15 CHECK HO2S SENSOR CIRCUIT FOR SHORT TO SIGRTN
  • Connect any disconnected HO2S sensor connectors.
  • Measure resistance between PCM pin E8 or PCM pin E9 and PCM pin E49.
  • Is the resistance greater than 10K ohms? 
 Yes GO to the next step.
No INSTALL a new HO2S sensor.
See HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 2.5L or HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 3.0L .
GO to step 29.
16 CHECK HO2S SENSOR CIRCUIT FOR SHORT TO GROUND
  • Measure the resistance between PCM pin E8 or PCM pin E9 and ground.
  • Is the resistance greater than 10K ohms? 
 Yes INSTALL a new PCM.
See POWERTRAIN CONTROL MODULE (PCM) REMOVAL/INSTALLATION - 2.5L or POWERTRAIN CONTROL MODULE (PCM) REMOVAL/INSTALLATION - 3.0L .
No INSTALL a new HO2S sensor.
See HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 2.5L or HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 3.0L .
GO to step 29.
17 HO2S CIRCUIT TEST (WITH RICH DTCs)
  • Disconnect suspect HO2S connector.
  • Key ON, engine running (KOER).
  • Access the PCM and monitor the HO2S signal PID using IDS or equivalent tester.
  • Is the voltage below 0.2 volt? 
 Yes Key OFF.
INSTALL a new HO2S sensor.
See HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 2.5L or HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 3.0L .
GO to step 29.
No Key OFF.
GO to the next step.
18 CHECK HO2S CIRCUIT FOR SHORT TO VPWR OR HEATER IN HARNESS
  • Key OFF.
  • PCM connector disconnected.
  • Measure the resistance between the HO2S signal circuit on the PCM connector harness side and HO2S heater circuit on the PCM connector harness side. Measure the resistance between the suspected HO2S signal circuit on the PCM connector harness and the VPWR circuit on the PCM connector harness side.
  • Are the resistances greater than 10K ohms? 
 Yes GO to step 29.
No REPAIR the short circuit. Clear the DTCs.
REPEAT self-test.
GO to step 29.
19 CHECK THE FUEL PRESSURE
WARNING:
  • When checking the fuel system remember that the fuel system may still be pressurized when the engine is switched off. Always follow the instructions related to fuel system pressure relief. All fuel handling safety precautions must be observed. Failure to follow these instructions may result in personal injury.
NOTE:
  • For vehicle specific fuel pressure ranges, see TEST 8: FUEL LINE/FUEL PRESSURE HOLD INSPECTION  .
  • Remove the jumper wire(s).
  • HO2S connector connected.
  • Relieve the fuel pressure. See FUEL SYSTEM PRESSURE RELEASE to pressurize the fuel system.
  • Mechanical fuel pressure gauge connected.
  • Pressurize the fuel system. See FUEL SYSTEM PRESSURE RELEASE to pressurize the fuel system.
  • Key ON, engine running (KOER).
  • Allow the fuel pressure to stabilize.
  • Key OFF.
  • Key ON, engine running (KOER).
  • Access the PCM and control the FP PID.
  • Run the fuel pump to obtain maximum fuel pressure.
  • Is the fuel pressure within range for the vehicle being diagnosed? 
 Yes GO to the next step.
No See TEST 8: FUEL LINE/FUEL PRESSURE HOLD INSPECTION  .
20 CHECK THE FUEL SYSTEM FOR PRESSURE STABILITY - FAST LEAK DOWN
NOTE:
  • When the fuel pump is commanded off, the fuel pressure may substantially decrease and then stabilize.
NOTE:
  • Key OFF.
  • Key ON, engine OFF (KOEO).
  • Access the PCM and control the FP PID.
  • Run the fuel pump to obtain maximum fuel pressure.
  • Command the fuel pump off.
  • Allow the fuel pressure to stabilize.
  • Record the stabilized reading.
  • Monitor the fuel pressure for 10 seconds.
  • Does the fuel pressure remain within 34 kPa (5 psi) of the recorded reading after 10 seconds? 
 Yes GO to step 22.
No GO to the next step.
21 CHECK FOR AN EXTERNAL FUEL LEAK
  • Inspect the fuel tank, lines and filler pipe for a fuel leak.
  • Is a concern present? 
 Yes REPAIR as necessary.
REFER to the TEST 4: FUEL DELIVERY SYSTEM .
See TEST 8: FUEL LINE/FUEL PRESSURE HOLD INSPECTION  .
CLEAR the DTCs. REPEAT the self-test.
GO to step 29.
No GO to step 23.
22 CHECK THE FUEL SYSTEM FOR PRESSURE STABILITY - SLOW LEAK DOWN
  • Continue to monitor the fuel pressure for 1 minute.
  • Does the fuel pressure remain within 34 kPa (5 psi) of the recorded reading (MRFS) or greater than 275 kPa (40 psi) (ERFS) after 1 minute? 
 Yes GO to the next step.
No See TEST 8: FUEL LINE/FUEL PRESSURE HOLD INSPECTION  .
23 FLOW TEST
  • Key OFF.
  • PCM connector connected.
  • Flow test the injector using the fuel injector tester.
  • Is the flow rate for each injector within specification? 
 Yes For DTC P0171 or P0174, GO to the next step.
For DTC P0172 or P0175, GO to step 25.
No INSTALL a new fuel injector.
See FUEL RAIL REMOVAL/INSTALLATION - 2.5L or FUEL RAIL REMOVAL/INSTALLATION - 3.0L 01-14A-29.
RESET the keep alive memory (KAM).
See ELECTRONIC ENGINE CONTROL (EEC) SYSTEM  .
REPEAT the self-test.
GO to step 29.
24 CHECK THE HO2S OUTPUT VOLTAGE
  • HO2S connector disconnected.
  • Visually inspect the HO2S circuit for exposed wiring, contamination, corrosion and correct assembly. Repair as necessary.
  • Measure the resistance between the HO2S signal circuit component side and SIGRTN circuit component side.
  • Increase the engine speed to 2000 RPM for 3 minutes.
  • Carry out the KOER self-test.
  • Monitor the signal voltage during the self-test.
  • Is the voltage greater than 0.5 volt at any time during the self-test? 
 Yes GO to the next step.
No INSTALL a new HO2S sensor.
See HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 2.5L or HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 3.0L .
RESET the keep alive memory (KAM).
See ELECTRONIC ENGINE CONTROL (EEC) SYSTEM  .
REPEAT the self-test.
GO to step 29.
25 ATTEMPT TO RETRIEVE DTC P0171 AND P0174
  • HO2S connector disconnected.
  • Connect a 5 amp fused jumper wire between the HO2S Signal circuit harness side and the battery negative terminal.
  • Carry out the KOER self-test.
  • Are DTCs P0171 and P0174 present? 
 Yes GO to the next step.
No GO to step 29.
26 HO2S VOLTAGE CHECK
  • Key OFF.
  • Remove the jumper wire(s).
  • HO2S connector disconnected.
  • Key ON, engine running (KOER).
  • Increase the engine speed to 2,000 RPM for 30 seconds.
  • Measure the voltage between HO2S signal component side and SIGRTN signal component side.
  • Carry out the KOER self-test.
  • Monitor the signal voltage during the self-test.
  • Is the voltage less than 0.4 volt at any time during the self-test? 
 Yes GO to the next step.
No INSTALL a new HO2S sensor.
See HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 2.5L or HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 3.0L .
RESET the keep alive memory (KAM).
See ELECTRONIC ENGINE CONTROL (EEC) SYSTEM  .
REPEAT the self-test.
GO to step 29.
27 CARRY OUT A THOROUGH WIGGLE TEST ON THE HO2S HARNESS
  • Key OFF.
  • HO2S connector connected.
  • Key ON, engine running (KOER).
  • Engine at normal operating temperature.
  • Access the PCM and monitor the HO2S signal PID.
  • Wiggle, shake and bend small area of the wiring harness while working from the sensor to the PCM.
  • While monitoring the HO2S PID, does the HO2S stop switching? 
 Yes ISOLATE the concern and REPAIR as necessary.
CLEAR the DTCs. REPEAT the self-test.
GO to step 29.
No GO to the next step.
28 TEST DRIVE THE VEHICLE WHILE MONITORING THE HO2S PID FOR SWITCHING
  • Access the PCM and monitor the HO2S signal and FUELSYS PIDs.
  • Start the engine and let idle until the vehicle goes into the closed loop fuel condition.
  • Key ON, engine running (KOER).
  • Drive the vehicle in a manner consistent with the freeze frame data in an attempt to simulate the original concern.
  • Does the HO2S PID switch? 
 Yes See MASS AIR FLOW (MAF) SENSOR  .
No INSTALL a new HO2S sensor.
See HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 2.5L or HEATED OXYGEN SENSOR (HO2S) AND CATALYST MONITOR SENSOR REMOVAL/INSTALLATION - 3.0L .
RESET the keep alive memory (KAM).
See ELECTRONIC ENGINE CONTROL (EEC) SYSTEM  .
REPEAT the self-test.
GO to the next step.
29 VERIFY TROUBLESHOOTING OF DTCs COMPLETED
  • Disconnect all the PCM connectors.
  • Check for:
    • corrosion
    • damaged pins
    • pushed-out pins
  • Connect all connectors and make sure they seat correctly.
  • Clear DTCs from PCM memory using IDS or equivalent tester generic OBD II tester.
  • Carry out the PCM Quick Test. See PCM QUICK TEST  .
  • Is the same DTC present? 
 Yes INSTALL a new PCM.
See POWERTRAIN CONTROL MODULE (PCM) REMOVAL/INSTALLATION - 2.5L or POWERTRAIN CONTROL MODULE (PCM) REMOVAL/INSTALLATION - 3.0L .
REPEAT the PCM Quick Test. See PCM QUICK TEST  .
No If any other DTC is present, GO to applicable DTC inspection.
If no DTC is present, troubleshooting complete.
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