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Adaptive Fuel Control

DTC P0171, P0172, P0174, P0175 DETECTION CONDITION AND POSSIBLE CAUSES

DTC P0171, P0172, P0174, P0175 ADAPTIVE FUEL CONTROL
DETECTION CONDITION 
  • DTC P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit.
  • DTC P0172 bank 1 (Cylinder 1) and DTC P0175 bank 2 indicate the fuel/air ratio is too rich. The fuel trim system is at the lean correction limit.
POSSIBLE CAUSE 
  • Fuel system:
    • Low fuel pressure or running out of fuel.
    • Excessive fuel pressure.
    • Leaking fuel injector(s).
    • Leaking fuel pressure regulator.
    • Vapor recovery system.
    • Contaminated fuel injector(s).
  • Induction system:
    • Air leaks after the MAF.
    • Vacuum leaks (vacuum lines and gaskets).
    • Restricted air inlet.
    • PCV system.
    • Improperly seated engine oil dipstick.
  • EGR system:
    • Leaking gasket.
    • Stuck EGR valve.
    • Leaking diaphragm or EVR.
  • Base engine:
    • Oil overfill.
    • Cam timing.
    • Cylinder compression.
    • Exhaust leaks before or near the HO2S(s).
DTC P0171, P0172, P0174, P0175 INSPECTION

STEP INSPECTION ACTION
1 DTCS P0172, P0174, P0171 and P0175: FUEL SYSTEM AT THE CORRECTED FUEL TRIM
NOTE: It is necessary to address all Continuous Memory Ignition and Misfire DTCs, if received during Continuous Memory testing, before addressing any Fuel Trim DTCs.
  • Check intake air system for leaks and damage.
  • Verify integrity of the PCV system.
  • Check for vacuum leaks.
  • Check air cleaner element, air cleaner housing for blockage.
  • Are any of the above concerns present? 
 Yes Repair as necessary.
Go to step 27.
No Go to step 2.
2 PERFORM KOER SELF TEST
  • NGS Tester connected.
  • Disconnect fuel vapor hose from intake manifold and plug fitting at intake manifold.
  • Start engine and run at 2,000 rpm for 5 minutes and return to idle.
  • Perform Key On Engine Running (KOER) self-test.
  • Key OFF.
  • Are any HO2S DTCs P1127, P1128, P1129, P1131, P1132, P1151 or P1152 present? 
 Yes DTC(s) P1127 Go to HO2S HEATER(S)  DTC(s) P1128 or P1129:
Go to HEATED OXYGEN SENSOR HO2S SIGNALS  and repair first.
DTC(s) P0131 or P0151:
See HEATED OXYGEN SENSOR (HO2S)  , Step 1.
DTC(s) P1131, P1130 or P1151, P1150:
Go to step 3.
DTC(s) P1132, P1130, or P1152, P1150:
Go to step 9.
No Continuous DTC(s) only P1130, P1150, P0171, P0174, P0172 and P0175:
Go to step 12.
If DTC(s) P1132 and/or P1152 are no longer present:
Reconnect vapor line.
All EVAP systems:
See EVAPORATIVE EMISSION (EVAP) SYSTEM MALFUNCTION  , step 9.
All others without recurring DTC(s):
The fault that produced the DTC is an intermittent.
See TEST 4: INTERMITTENT  Step 1 with the following data: HO2S-11 and HO2S-21 PIDs and list of possible causes.
3 HO2S CIRCUIT TEST (WITH LEAN DTCS)
  • NGS Tester connected.
  • Disconnect the HO2S related to the DTC.
  • Key On Engine Off (KOEO).
  • Access the correct HO2S PID.
    NOTE: If arcing occurs, indicating a short, remove jumper and go to step 7 (check fuse in heater circuit).
  • Jumper HO2S Signal circuit to the HO2S Heater VPWR Circuit at the HO2S vehicle harness connector.
  • Is the reading 1.30 volts or greater? 
 Yes CHECK SIG RTN circuit.
Go to step 4.
No Go to step 6.
4 CHECK SIGNAL RETURN CIRCUIT FOR SHORTS AND OPENS
  • Install Breakout Box, PCM connected.
  • Measure resistance of HO2S SIG RTN circuit between the HO2S vehicle harness connector and the battery ground terminal.
  • Is the resistance reading less than 5.0 ohms? 
 Yes Reconnect all components.
Go to step 12.
No CHECK wiring.
Go to step 5.
5 CHECK HO2S SIGNAL RETURN CIRCUIT IN VEHICLE HARNESS
  • PCM disconnected.
  • Measure resistance of the HO2S SIG RTN circuit between the HO2S vehicle harness connector and PCM test pin 91.
  • Is resistance reading less than 5.0 ohms? 
 Yes Replace PCM. See POWERTRAIN CONTROL MODULE .
Go to step 27.
No Repair open circuit.
Go to step 27.
6 CHECK RESISTANCE OF HO2S AND HO2S GROUND CIRCUITS
  • Disconnect PCM.
  • Install Breakout Box, PCM disconnected.
  • Measure resistance of HO2S Signal circuit between PCM test pin and HO2S vehicle harness connector.
  • Use pin assignments below and record the following:
    • HO2S-11 SIG = test pin 60
    • HO2S-21 SIG = test pin 87
    • HO2S SIG RTN = test pin 91
    • Is the resistance reading less than 5.0 ohms? 
 Yes Go to step 7.
No Repair open circuit.
Go to step 27.
7 CHECK HO2S CIRCUIT WIRING HARNESS FOR SHORT TO GROUND
  • Measure resistance between HO2S signal circuit PCM test pin and PCM test pins 24, 51, 77, 103 (PWR GND) and 91 (SIG RTN).
  • Is each resistance greater than 10,000 ohms? 
 Yes Go to step 8.
No Repair short circuit.
Go to step 27.
8 CHECK HO2S FOR SHORT TO GROUND
  • Reconnect HO2S.
  • Measure resistance between PWR GND and SIG RTN PCM test pins and HO2S signal circuit PCM test pin.
    • HO2S-11 SIG = test pin 60
    • HO2S-21 SIG = test pin 87
    • HO2S GND = test pins 24 and 103
    • HO2S SIG RTN = test pin 91
    • Is resistance greater than 10,000 ohms? 
 Yes Replace PCM. See POWERTRAIN CONTROL MODULE .
Go to step 27.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL & INSTALLATION article .
Go to step 27.
9 HO2S CIRCUIT CHECK (FOR RICH DTCS)
  • Key OFF.
  • Disconnect HO2S related to the DTC received.
  • NGS Tester connected.
  • Key ON.
  • Access HO2S PID(s).
  • Is the reading less than 0.2 volt? 
 Yes Go to step 11.
No Go to step 10.
10 CHECK FOR SHORTS TO VOLTAGE SOURCE IN THE HARNESS CIRCUIT
  • Key OFF.
  • Disconnect NGS Tester from DLC.
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Use the following list to measure resistance between the appropriate PCM test pins:
    • DTC P1130, P1132 = HO2S-11 test pin 60 and test pins 71 and 93
    • DTC P1150, P1152 = HO2S-21 test pin 87 and test pins 71 and 94
    • Is each resistance greater than 10,000 ohms? 
 Yes Replace PCM. See POWERTRAIN CONTROL MODULE .
Go to step 27.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL & INSTALLATION article .
Go to step 27.
11 CHECK FOR HO2S SIGNAL SHORTED TO HO2S HEATER CIRCUIT IN THE SENSOR
  • Suspect HO2S sensor connected.
  • NGS Tester connected.
  • Key On Engine Off (KOEO).
    NOTE: HO2S displayed as O2S on NGS Tester.
  • Access HO2S PID corresponding to the DTCs received.
  • Is the HO2S voltage greater than 0.45 volt? 
 Yes Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL & INSTALLATION article .
Go to step 27.
No Reconnect all components.
Go to step 12.
12 CHECK FUEL PRESSURE
WARNING: The fuel system is pressurized when the engine is not running. To prevent injury or fire, use caution when working on the fuel system.
  • Connect battery charger.
  • Install fuel pressure gauge.
  • Key on, engine off.
  • Access output test mode and run the fuel pump to obtain maximum fuel pressure.
  • No Start:
  • Is the fuel pressure between 386-496 kPa (56-72 psi), 3.0L flexible fuel 380-517 kPa (55-75 psi)? 
 Yes Key OFF
For 3.0L flex fuel go to step 13.
All others go to step 15.
No Go to fuel delivery tests.
See TEST 5: FUEL DELIVERY SYSTEM  .
13 CHECK SYSTEM ABILITY TO HOLD FUEL PRESSURE
  • Cycle the key on and off several times.
  • Verify there are no external leaks (repair as necessary).
  • Does the fuel pressure remain within 34 kPa (5 psi) of the highest reading after one minute? 
 Yes For Continuous DTCs P1130, P1150, P0171, P0172, P0174 and P0175:
Go to step 14.
For HO2S DTCs displayed with misfire DTCs:
Go to step 16.
All other DTCs:
Go to step 19.
No Go to fuel delivery tests.
See TEST 5: FUEL DELIVERY SYSTEM  .
14 CHECK SYSTEM ABILITY TO HOLD FUEL PRESSURE WITH KEY ON
  • Cycle key on and off several times.
  • Key on and engine off, monitor fuel pressure gauge.
  • Does fuel pressure remain within 34 kPa (5 psi) of the highest reading after 10 seconds? 
 Yes For Continuous DTCs P1130, P1150, P0171 and P0174:
Go to step 16.
No For DTCs P0172 and P0175:
Go to step 15.
15 CHECK INJECTOR FAULT PIDS
  • Access INJ1F-INJ6F PIDs.
    NOTE: If misfire DTCs are present, access only injector fault PIDs corresponding to misfire DTCs.
  • Is an injector fault present? 
 Yes Go to step 16.
No Go to step 19.
16 CHECK FUEL INJECTOR(S) AND HARNESS RESISTANCE
NOTE: This will erase Continuous Memory DTCs.
  • Disconnect PCM.
    NOTE: Use the injector fault PID to determine the fuel injector circuit(s) requiring testing.
  • Measure the resistance between suspect fuel injector and VPWR circuits (R) pin 71 at the PCM harness connector.
  • Is the resistance between 11.0 and 18.0 ohms? 
 Yes Replace PCM. See POWERTRAIN CONTROL MODULE .
Go to step 27.
No Go to step 17.
17 CHECK RESISTANCE OF FUEL INJECTOR HARNESS
  • Disconnect harness connector at the suspect fuel injector.
  • Measure resistance of fuel injector circuit between PCM test pin 71 (VPWR) and the VPWR pin at the fuel injector harness connector.
  • Measure resistance of fuel injector circuit between PCM test pins and the fuel injector signal pin at the fuel injector harness connector.
  • Is each resistance less than 5.0 ohms? 
 Yes Go to step 18.
No Repair open circuit.
Go to step 27.
18 CHECK FUEL INJECTOR HARNESS CIRCUIT FOR SHORT TO POWER OR GROUND
  • Disconnect PCM.
  • Measure resistance between fuel injector signal circuit PCM test pin(s) and PCM test pin 71 (VPWR), 24 and 103 (PWR GND).
  • Is each resistance greater than 10,000 ohms? 
 Yes Go to step 19.
No Repair short circuit.
Go to step 27.
19 FLOW TEST FUEL INJECTORS
  • Use a fuel injector tester to flow test the fuel injectors according to the instructions for the fuel injector tester.
  • Is the leakage flow within specification? 
 Yes For DTCs P0171 and P0174:
Go to step 20.
For DTCs P0172 and P0175:
The fault that caused the DTC is an intermittent.
See TEST 4: INTERMITTENT  .
For DTCs P1130, P01131, P1150 and P1151:
Go to step 20.
For DTCs P1132 and P1152:
Go to step 23.
No Replace fuel injector.
See FUEL RAILS & INJECTORS in REMOVAL, OVERHAUL & INSTALLATION article
20 INSPECT INDUCTION SYSTEM FOR AIR LEAKS
  • Inspect the following areas for signs of air leaks:
    • Inlet tube(s) from air cleaner to throttle body.
    • Gaskets which seal the upper and lower intake manifold.
    • Vacuum hoses and lines for cracks and proper connections.
    • PCV system.
    • Are there any signs of leaks or damage? 
 Yes Repair as necessary.
Go to step 27.
No For DTCs P0171, P0174, P1130 or P1150:
The fault that caused the DTC is an intermittent.
See TEST 4: INTERMITTENT  .
For DTCs P1131 and P01130 or P1151 and P1150:
Go to step 21.
21 CHECK CYLINDER COMPRESSION
  • Check cylinder compression.

    See ENGINE COMPONENT TESTS  .

    NOTE: Use Misfire DTCs (if present) to determine which cylinder's compression to check. Otherwise check all cylinders.
  • Are cylinder compression readings within specification? 
 Yes For DTCs P1131, P1130, P1151 and P1150:
Go to step 22.
For DTCs P1132 and P1152:
Go to step 23.
Misfire DTCs are displayed with fuel control DTCs:
See MISFIRE DETECTION MONITOR  .
No Repair as necessary.
Go to step 27.
22 CHECK HO2S ABILITY TO GENERATE A VOLTAGE GREATER THAN 0.5 VOLT
NOTE: Any vacuum air leaks can cause DTCS P1131, P1130, P1151 and P1150.
  • Inspect HO2S harness for chafing, burned wiring or other damage and repair as necessary.
  • Disconnect the suspect HO2S from vehicle harness.
  • Connect multimeter to HO2S signal and HO2S SIG RTN or HO2S GND at the HO2S sensor connector.
  • Run engine at 2,000 rpm for three minutes.
  • Run KOER self-test and monitor HO2S voltage.
  • Key OFF.
  • Was voltage greater than 0.5 volt during or at the end of self-test? 
 Yes Go to step 25.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) .
Go to step 27.
23 ATTEMPT TO GENERATE DTCS P1131 AND P1151
  • HO2S disconnected.
  • Jumper HO2S Signal at the HO2S harness vehicle connector to the battery negative post.
  • Activate Key On Engine Running (KOER) Self Test.
  • Are DTCs P1131 or P1151 present? 
 Yes Remove jumper.
Go to step 24.
No Remove jumper.
Reconnect HO2S.
Disconnect PCM.
Inspect both sides for damaged or pushed out pins, corrosion, moisture and loose pins.
Repair as necessary.
If OK, replace PCM. See POWERTRAIN CONTROL MODULE .
Rerun KOER Self Test.
24

HO2S SENSOR VOLTAGE CHECK

  • Suspect HO2S disconnected.
  • Connect multimeter to HO2S SIG circuit and HO2S SIG RTN at the HO2S sensor connector.
  • Disconnect vacuum hose from vacuum tree.
  • Start engine and run at 2,000 rpm.
  • Key OFF.
  • Did voltage reading indicate less than 0.4 volt within 30 seconds? 
 Yes Reconnect vacuum hose and HO2S.
Go to step 25.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) .
Go to step 27.
25 MONITOR HO2S (PID) FOR PROPER SWITCHING
  • Key On Engine Running (KOER).
  • Engine at operating temperature.
    NOTE: HO2S is displayed as O2S on NGS Tester.
  • Monitor suspect HO2S PID using NGS Tester.
  • Access HO2S PID while wiggling, bending and shaking small sections of the engine harness from the HO2S to the PCM.
  • Key OFF.
  • Did the HO2S voltage stay high (greater than 0.45 volt) or low (less than 0.45 volt)? 
 Yes Isolate cause of lack of HO2S switching and repair as necessary.
Go to step 27.
No Go to step 26.
26 TEST DRIVE WHILE MONITORING HO2S PID FOR PROPER SWITCHING
NOTE: This step requires an observer to monitor PID for proper operation.
  • NGS Tester still attached.
  • Access HO2S PID.
  • While observer views PID, test drive vehicle under different road conditions in an attempt to simulate the original fault.
  • Does HO2S appear to switch properly? 
 Yes Unable to duplicate fault.
Go to step 27.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL & INSTALLATION article .
Go to step 27.
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