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Upstream Heated Oxygen Sensor (Ho2S) Not Switching

DTC P1131, P1151 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P1131, P1151 UPSTREAM HEATED OXYGEN SENSOR (HO2S) NOT SWITCHING
DETECTION CONDITION 
  • P1131 (Bank 1) and P1151 (Bank 2) indicate HO2S sensor is indicating lean at the end of a test trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects a switch for a calibrated amount of time.
POSSIBLE CAUSE 
  • Fuel system:
    • Leaking fuel injector(s).
    • Leaking fuel pressure regulator.
    • Low fuel pressure or running out of fuel.
    • Contaminated fuel injector(s).
  • Induction system:
    • Air leaks after the MAR
    • Vacuum leaks (vacuum lines and gaskets).
    • Improperly seated engine oil dipstick.
  • EGR system:
    • Leaking gasket.
    • Stuck open EGR valve.
    • Leaking diaphragm.
  • Base engine:
    • Oil overfill.
    • Cam timing.
    • Cylinder compression.
    • Exhaust leaks before or near HO2S(s).
  • Electrical:
    • Water in harness connector.
    • Corrosion or poor mating terminals and wiring.
    • Open/shorted HO2S to ground.
    • Damaged HO2S.
    • Damaged PCM.
HINT  HO2S Sensor Description 
  • Detects the presence of oxygen in the exhaust and produces a variable voltage (0.0 -1.1 V) according to the amount of oxygen detected.
    • A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a low voltage signal (less than 0.4 V).
    • A low concentration of oxygen (rich air/fuel ratio) in the exhaust produces a high voltage signal (greater than 0.6 V).
  • Provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation.
G03988150Courtesy of MAZDA MOTORS CORP.
DTC P1131, P1151 INSPECTION

STEP INSPECTION ACTION
1
  • Was PCM Quick Test performed? 
 Yes Go to next step.
No Perform PCM Quick Test.
2 DTCS P1131, P1151: UPSTREAM HO2S(S) NOT SWITCHING
  • Check air intake system for leaks and damage.
  • Verify integrity of PCV system.
  • Check for vacuum leaks.
  • Are any of the above concerns present? 
 Yes Repair as necessary.
Go to step 21.
No Go to next step.
3 PERFORM KOER SELF TEST
  • 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 KOER Self Test.
  • Is DTC P1131 and/or P1151 present? 
 Yes Go to next step.
No Perform EVAP LEAK TEST to locate EVAP system leak. See EVAPORATIVE EMISSION SYSTEM LEAK TEST .
4 HO2S CIRCUIT TEST (WITH LEAN DTCS)
  • Key OFF.
  • Disconnect suspect HO2S related to the DTC.
    • P1131 = HO2S11 (Front RH).
    • P1151 = HO2S21 (Front LH).
  • Key ON, Engine OFF (KOEO).
  • Access O2S11 (Front RH) or O2S21 (Front LH) PID using NGS Tester.
    NOTE: If a spark occurs, indicating a short, remove jumper and check for short to ground (check fuse in heater circuit).
  • Jumper HO2S SIG to HO2S VPWR at the HO2S vehicle harness connector.
  • Is the reading 1.30 V or greater? 
 Yes Go to next step.
No An open or short to ground exists in the vehicle harness or PCM.
Go to step 7.
5 CHECK SIGNAL RETURN CIRCUIT FOR SHORTS AND OPENS
  • 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 10.
No Check wiring for open or short to ground.
Go to next step.
6 CHECK HO2S SIGNAL RETURN CIRCUIT IN VEHICLE HARNESS
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Measure resistance of the HO2S SIG RTN circuit between PCM test pin 91 and the HO2S vehicle harness connector.
  • Is resistance reading less than 5.0 ohms? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 21.
No Repair open circuit.
Go to step 21.
7 CHECK RESISTANCE OF HO2S GROUND CIRCUITS
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Measure resistance of HO2S SIG circuit between PCM test pin and the HO2S vehicle harness connector. Use the following pin assignment and record the reading:
    • HO2S-11 SIG = PCM test pin 60.
    • HO2S-21 SIG = PCM test pin 87.
  • Is the resistance reading less than 5.0 ohms? 
 Yes Go to next step.
No Repair open circuit.
Go to step 21.
8 CHECK HO2S CIRCUIT WIRING HARNESS FOR SHORT TO GROUND
  • Measure resistance between HO2S SIG circuit between PCM test pin 103 (PWR GND).
  • Measure resistance between HO2S SIG circuit between PCM test pin 60 or 87 and PCM test pin 91 (SIG RTN).
  • Is each resistance greater than 10K ohms? 
 Yes Go to next step.
No Repair short circuit.
Go to step 21.
9 CHECK HO2S FOR SHORT TO GROUND
  • Reconnect HO2S.
  • Measure resistance between HO2S SIG circuit between PCM test pin 60 or 87 and PCM test pin 103 (PWR GND).
  • Measure resistance between HO2S SIG circuit between PCM test pin 60 or 87 and PCM test pin 91 (SIG RTN).
  • Is each resistance greater than 10K ohms? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 21.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Go to step 21.
10 CHECK HO2S ABILITY TO GENERATE A VOLTAGE GREATER THAN 0.5 VOLT
  • Inspect HO2S harness for wear from rubbing, burned wiring or other damage and repair as necessary.
  • Disconnect the suspect HO2S from vehicle harness.
  • Connect multimeter to HO2S SIG 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.

    See ON-BOARD DIAGNOSTIC TESTS .

  • Key OFF.
  • Was voltage greater than 0.5 V during or at the end of Self Test? 
 Yes Go to next step.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Go to step 21.
11 MONITOR HO2S (PID) FOR PROPER SWITCHING
  • Access O2S11 (Front RH) or O2S21 (Front LH) 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 V) or low (less than 0.45 V)? 
 Yes Isolate cause of lack of HO2S switching and repair as necessary.
Go to step 21.
No Go to next step.
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.
  • Install fuel pressure gauge.
  • Key ON, Engine OFF (KOEO).
  • Access Output Test Mode and run the fuel pump to obtain maximum fuel pressure.
    NOTE: The fuel pump will only operate for approximately 8 seconds when Output Test Mode is selected and activated.
  • Is the fuel pressure 30--65 psi (207--448 kPa)? 
 Yes Fuel system is capable of required fuel pressure.
Go to next step.
No See TEST 5: FUEL DELIVERY SYSTEM .
13 CHECK INJECTOR FAULT PIDS
  • Access INJ1F-INJ6F PIDs using NGS Tester.
  • Is an injector(s) fault present? 
 Yes Go to next step.
No Go to step 17.
14 CHECK FUEL INJECTOR(S) AND HARNESS RESISTANCE
NOTE: This erases Continuous Memory DTCs.
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected. Note Use the injector fault PID to determine the fuel injector circuit(s) requiring testing.
  • Measure resistance of suspect fuel injector between suspect INJ circuit and PCM test pin 71 (VPWR).
  • Is the resistance between 11.0-18.0 ohms? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 21.
No Go to next step.
15 CHECK FUEL INJECTOR HARNESS RESISTANCE
  • Disconnect fuel injector harness connector at the suspect fuel injector.
  • Measure resistance between suspect INJ circuit PCM test pin and PCM test pin 71 (VPWR).
  • Measure resistance between suspect INJ circuit PCM test pin and PCM test pin 103 (PWR GND).
  • Is each resistance less than 5.0 ohms? 
 Yes Go to next step.
No Repair open harness circuit.
Go to step 21.
16 CHECK FUEL INJECTOR HARNESS CIRCUIT FOR SHORT TO POWER AND GROUND
  • Measure resistance between INJ at suspect fuel injector and PCM test pin 71 or 97 (VPWR).
  • Measure resistance between INJ at suspect fuel injector and PCM test pin 51 or 103 (PWR GND).
  • Is each resistance greater than 10K ohms? 
 Yes Go to next step.
No Repair short circuit.
Go to step 21.
17 FLOW TEST FUEL INJECTOR(S)
  • Use a fuel injector tester to flow test the fuel injectors according to the instructions for the tester.
  • Flow rate specification is 14 lb/hr (6.4 kg/hr) for gas engines and 19 lb/hr (8.6 kg/hr) for the 3.0L Flexible Fuel engine.
  • Is the leakage and flow within specification? 
 Yes Go to next step.
No Replace fuel injector(s).
See FUEL RAILS & INJECTORS in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance .
Go to step 21.
18 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 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 21.
No Go to next step.
19 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 Go to next step.
No Repair as necessary.
Go to step 21.
20 TEST DRIVE WHILE MONITORING HO2S PID FOR PROPER SWITCHING
NOTE: This step requires an observer to monitor PID for proper operation.
  • Access O2S11 (Front RH) or O2S21 (Front LH) 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 21.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Go to step 21.
21 VERIFY TROUBLESHOOTING OF DTCs COMPLETED
  • Make sure to reconnect all disconnected connectors.
  • Clear DTCs from PCM memory using NGS tester generic OBD-II function.
  • Perform PCM Quick Test.
  • Is same DTC present? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Repeat PCM Quick Test.
No If any other DTC is present, go to applicable DTC inspection.
If no DTC is present, troubleshooting complete.


DTC P1132, P1152 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P1132, P1152 UPSTREAM HEATED OXYGEN SENSOR (HO2S) NOT SWITCHING
DETECTION CONDITION 
  • P1132 (Bank 1) and P1152 (Bank 2) indicate HO2S sensor is indicating rich at the end of a test trying to correct for an over-lean condition. The test fails when the fuel control system no longer detects a switch for a calibrated amount of time.
POSSIBLE CAUSE 
  • Fuel system:
    • Excessive fuel pressure.
    • Contaminated fuel injector(s).
  • Induction system:
    • PCV system.
  • EGR system:
    • Stuck open EGR valve.
    • Leaking diaphragm.
  • Base engine:
    • Oil overfill.
    • Cam timing.
  • Electrical:
    • Short to power source in harness or HO2S.
    • Water in harness connector.
    • Damaged HO2S.
    • Damaged PCM.
HINT  HO2S Sensor Description 
  • Detects the presence of oxygen in the exhaust and produces a variable voltage (0.0 -1.1V) according to the amount of oxygen detected.
    • A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a low voltage signal (less than 0.4 V).
    • A low concentration of oxygen (rich air/fuel ratio) in the exhaust produces a high voltage signal (greater than 0.6 V).
  • Provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation.
G03988151Courtesy of MAZDA MOTORS CORP.
DTC P1132, P1152 INSPECTION

STEP INSPECTION ACTION
1
  • Was PCM Quick Test performed? 
 Yes Go to next step.
No Perform PCM Quick Test.
2 DTCS P1132 AND P1152: UPSTREAM HO2S(S) NOT SWITCHING
  • Check air intake system for obstructions or damage.
  • Check air cleaner element, air cleaner housing for blockage.
  • Check PCV system for proper hose routing.
  • Are any of these concerns present? 
 Yes Repair as necessary.
Go to step 17.
No Go to next step.
3 PERFORM KOER SELF TEST
  • 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.
  • Is DTC P1132 and/or P1152 present? 
 Yes Go to next step.
No Purge solenoid may be stuck open.
Go to EVAP Emission System Leak Test. See EVAPORATIVE EMISSION SYSTEM LEAK TEST .
4 HO2S CIRCUIT CHECK (WITH RICH DTCS)
  • Key OFF.
  • Disconnect suspect HO2S related to the DTC.
    • P1132 = HO2S11 (Front RH).
    • P1152 = HO2S21 (Front LH).
  • Key ON, Engine Running (KOER).
  • Access O2S11 (Front RH) or O2S21 (Front LH) PID.
  • Is the reading 0.2 V or less? 
 Yes Go to step 6.
No A short to power exists.
Go to next step.
5 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.
  • For DTC P1132, measure the resistance between PCM test pin 60 and PCM test pins 71 (VPWR) and 93 (HTR11)
  • For DTC 1152, measure the resistance between PCM test pin 87 and PCM test pins 71 (VPWR) and 94 (HTR21)
  • Is the resistance greater than 10K ohms? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 17.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Repair short to power.
Go to step 17.
6 CHECK FOR HO2S SIGNAL SHORTED TO HO2S HEATER CIRCUIT IN THE SENSOR
  • Reconnect suspect HO2S sensor.
  • Key ON, Engine OFF (KOEO).
  • Access O2S11 (Front RH) or O2S21 (Front LH) PID.
  • Is the HO2S voltage greater than 0.45 V? 
 Yes Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Go to step 17.
No Reconnect all components.
Go to next step.
7 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 (KOEO).
  • Access Output Test Mode and run the fuel pump to obtain maximum fuel pressure.
    NOTE: The fuel pump will only operate for approximately 8 seconds when Output Test Mode is selected and activated.
  • Is the fuel pressure 30--65 psi (207--448 kPa)? 
 Yes Fuel system is capable of required fuel pressure.
Go to next step.
No See TEST 5: FUEL DELIVERY SYSTEM .
8 CHECK INJECTOR FAULT PIDS
  • Access INJ1F-INJ6F PIDs using NGS Tester.
  • Is an injector(s) fault present? 
 Yes Go to next step.
No Go to step 17.
9 CHECK FUEL INJECTOR(S) AND HARNESS RESISTANCE
NOTE: This erases Continuous Memory DTCs.
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
    NOTE: Use the injector fault PID to determine the fuel injector circuit(s) requiring testing.
  • Measure resistance between suspect INJ circuit PCM test pin and PCM test pin 71 (VPWR).
  • Is the resistance between 11.0-18.0 ohms? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 17.
No Go to next step.
10 CHECK FUEL INJECTOR HARNESS RESISTANCE
  • Disconnect fuel injector harness connector at the suspect fuel injector.
  • Measure resistance of VPWR circuit between PCM test pin 71 and the fuel injector harness connector.
  • Measure resistance of INJ circuit between appropriate PCM test pin and the fuel injector harness connector.
  • Is each resistance less than 5.0 ohms? 
 Yes Go to next step.
No Repair open harness circuit.
Go to step 17.
11 CHECK FUEL INJECTOR HARNESS CIRCUIT FOR SHORT TO POWER AND GROUND
  • Measure resistance between suspect INJ circuit PCM test pin and PCM test pin 71 (VPWR).
  • Measure resistance between suspect INJ circuit PCM test pin and PCM test pin 103 (PWR GND).
  • Is each resistance greater than 10K ohms? 
 Yes Go to next step.
No Repair short circuit.
Go to step 17.
12 FLOW TEST FUEL INJECTOR(S)
  • Use a fuel injector tester to flow test the fuel injectors according to the instructions for the tester.
    • Flow rate specification is 14 lb/hr (6.4 kg/hr) for gas engines and 19 lb/hr (8.6 kg/hr) for the 3.0L Flexible Fuel engine.
  • Is the leakage and flow within specification? 
 Yes Go to next step.
No Replace fuel injector(s).
See FUEL RAILS & INJECTORS in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance .
Go to step 17.
13 ATTEMPT TO GENERATE DTCS P1131 AND P1151
  • Disconnect suspect HO2S.
  • Jumper HO2S SIG at the HO2S harness vehicle connector to the battery negative post.
  • Perform Key ON, Engine Running (KOER) Self Test.
  • Are DTCs P1131 or P1151 present? 
 Yes Remove jumper.
Go to next step.
No Remove jumper.
Reconnect HO2S.
Disconnect PCM.
Inspect both ends for damaged or pushed out pins, corrosion and loose wires.
Repair as necessary.
If OK, replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 17.
14 HO2S CHECK
  • Connect multimeter to HO2S SIG circuit and HO2S SIG RTN at the HO2S sensor connector.
  • Disconnect any vacuum hose.
  • Start engine and run at 2, 000 rpm.
  • Does the voltage reading indicate less than 0.4 V within 30 seconds? 
 Yes Reconnect vacuum hose.
Go to next step.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Go to step 17.
15 MONITOR HO2S (PID) FOR PROPER SWITCHING
  • Key ON, Engine Running (KOER)
  • Engine at operating temperature.
  • Access O2S11 (Front RH) or O2S21 (Front LH) 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 V) or low (less than 0.45 V)? 
 Yes Isolate cause of lack of HO2S switching and repair as necessary.
Go to step 17.
No Go to next step.
16 TEST DRIVE WHILE MONITORING HO2S PID FOR PROPER SWITCHING
NOTE: This step requires an observer to monitor PID for proper operation.
  • Access O2S11 (Front RH) or O2S21 (Front LH) 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 17.
No Replace HO2S.
See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL AND INSTALLATION article in Engine Performance .
Go to step 17.
17 VERIFY TROUBLESHOOTING OF DTCs COMPLETED
  • Make sure to reconnect all disconnected connectors.
  • Clear DTCs from PCM memory using NGS tester generic OBD-II function.
  • Perform PCM Quick Test.
  • Is same DTC present? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Repeat 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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