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Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. Only use this test to diagnose the following:

NOTE: HO2S may be displayed on scan tester as 02S.

To prevent replacement of good components, be aware the following non-EEC areas may be cause of driveability concerns:

CIRCUIT TEST ACRONYMS

Acronym Definition
DLC Data Link Connector
HO2S Heated Oxygen Sensor
PID Parameter Identification
Fig 1: Identifying HO2S Connector Terminal
G95D35967
Fig 2: Identifying Fuel Injector Connector Terminals
G95F35969
Fig 3: Locating HO2S
G95I35970
HO2S TEST PIN IDENTIFICATION (1)

HO2S Pin No. HO2S SIG HO2S HTR
11 60 93
12 35 95
21 87 94
22 61 96
(1) SIG RTN is test pin No. 91. VPWR is test pin No. 71 and 97.
NOTE: Test procedure begins with step 20). No test procedures have been omitted.
  1. 20) Perform KOER Self-Test  If DTC P1127, P1128 or P1129 are present, service before proceeding. If specified DTCs are not present, go to next step.
  2. 21) DTC P0133 & P0153  This code indicates that response rate is below calibration in HO2S as follows:
    • DTC P0133 for right front (or front, except V8) HO2S.
    • DTC P0153 for left front (or rear, except V8) HO2S.

    Possible causes are as follows:

    • Open or shorted circuit.
    • Exhaust leak.
    • Excessive fueling.
    • HO2S coated with contaminants.
    • Faulty MAF sensor.
    • Leak in air induction system.

    With scan tester connected, turn ignition on. Access Generic OBD-II functions and enter. Select Diagnostic Monitoring Test Results and enter. Scroll to Test ID: 01 and enter. Press Start. If measured value is 614 or more, fault cannot be duplicated or identified at this time and testing is complete. If measurement fault is less than 614, go to next step.

  3. 22) Check For HO2S Contamination  Check following possibilities as potential source of contamination:
    • Use of unapproved silicon sealers.
    • Use of unapproved cleaners.
    • Fuel contaminated by silicon additives.
    • Fuel contaminated by lead.
    • Excessive oil burning.
    • Antifreeze leaking internally.

    If any of these conditions are present, repair or replace as necessary. Replace HO2S. Change oil, filter and repeat QUICK TEST. If none of these conditions are present, go to next step.

  4. 23) Check For Unmetered Air Leaks  Vacuum or air leaks in non-EEC-V areas could cause fault code to set. Check the following as potential source of air leak:
    • Leaking vacuum hoses.
    • Leaking intake manifold gasket.
    • EGR system.
    • PCV system.
    • Poorly seated oil dip stick and/or dipstick tube.

    If any of these conditions are present, repair or replace as necessary. Perform drive cycle and repeat QUICK TEST. If none of these conditions are present, go to next step.

  5. 24) Check HO2S Circuits  Turn ignition off. Disconnect PCM and suspect HO2S wiring harness connector. Inspect connectors for damage and repair as necessary. Connect jumper wire between HO2S SIG and VPWR at sensor wiring harness connector. With scan tester connected to DLC, turn ignition on. Access HO2S PID. If PID voltage is less than 1.5 volts, go to next step. If PID voltage is 1.5 volts or more, replace HO2S and change engine oil. Test drive vehicle and repeat QUICK TEST.
  6. 25) Check HO2S Signal Circuit Resistance  Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for damage and repair if necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between suspect HO2S test pin at breakout box and HO2S terminal at wiring harness connector. Measure resistance between suspect SIG RTN test pin at breakout box and SIG RTN terminal at wiring harness connector. If either resistance is 5 ohms or more, repair open circuit. Drive vehicle at 55 MPH for 5 minutes and repeat QUICK TEST. If each resistance is less than 5 ohms, go to next step.
  7. 26) Check HO2S For Short Circuit  Ensure ignition is off and PCM is disconnected. Disconnect scan tester from DLC. Measure resistance between suspect HO2S test pin and test pins No. 71 and 97 (VPWR) at breakout box. Measure resistance between suspect HO2S test pin and test pin No. 91 (SIG RTN) at breakout box. If either resistance is less than 10,000 ohms, repair short circuit. Drive vehicle for 5 miles at 55 MPH and repeat QUICK TEST. If each resistance is 10,000 ohms or more, replace PCM.
  8. 27) DTC P0131 & P0151: Contaminated HO2S/Voltage Shift  These DTCs are set when HO2S generates negative voltage. Possible causes are as follows:
    • Crossed HO2S SIG / SIG RTN circuit.
    • HO2S contaminated with water, fuel, etc.

    Check for moisture in HO2S connector and repair if necessary. If connector is okay, go to next step.

  9. 28) Check HO2S For Short Circuit  Ensure ignition is off. Disconnect suspect HO2S. Disconnect PCM 104-pin connector. Inspect connectors for damage and repair if necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between suspect sensor HO2S SIGNAL and SIG RTN terminal and test pins indicated as follows:
    • DTC P0131, test pin No. 60.
    • DTC P0151, test pin No. 87.

    If resistance is less than 5 ohms, replace HO2S and repeat QUICK TEST. If resistance is 5 ohms or more, repair circuit and repeat QUICK TEST.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 28) to step 30). No test procedures have been omitted.
  10. 30) DTC P0135, P0141, P0155 Or P0161: Check HO2S Heater Signal Circuit  DTCs P0135, P0141, P0155 and P0161 received separately indicate a short to ground or open in HO2S heater circuit. DTCs received in pairs, such as P0135 and P0155 or P0141 and P0161, indicate HO2S heater signal circuit shorted to a power source greater than 2.0 volts. DTCs received in pairs with one downstream heater code and one upstream heater code are treated as the following separate codes:
    • DTC P0135 for right front HO2S.
    • DTC P0155 for left front HO2S.
    • DTC P0141 for right rear HO2S.
    • DTC P0161 for left rear HO2S.

    Possible causes are as follows:

    • Signal shorted in wiring harness or HO2S.
    • Water in connectors.
    • Cut or pulled wires.
    • Open in PWR GND or VPWR circuit.

    Inspect HO2S connectors for damage or poor connection. Repair or replace connectors as necessary. If HO2S connectors are okay, go to next step.

  11. 31) Perform KOEO Self-Test  Start engine and operate at 2000 RPM for 5 minutes. Turn ignition off. Perform KOEO self-test. If DTC P0135, P0141, P0155 or P0161 are present, go to next step. If specified DTCs are not present, go to CIRCUIT TEST Z .
  12. 32) Check For Voltage At HO2S Heater Wiring Harness Connector  Turn ignition off. Disconnect suspect HO2S. Inspect wiring harness for damage and repair as necessary. Turn ignition on. Measure voltage between SIG RTN and VPWR terminal at HO2S wiring harness connector. If voltage is 10.5 volts or less, go to next step. If voltage is more than 10.5 volts, go to step 34).
  13. 33)  Turn ignition off. With suspect sensor disconnected, measure resistance between VPWR terminal at HO2S wiring harness connector and test pins No. 71 and 97 at breakout box. If resistance is less than 4 ohms, go to next step. If resistance is 4 ohms or more, check circuit fuse. If fuse is okay, repair open circuit and repeat QUICK TEST.
  14. 34) Check HO2S Heater Resistance  Turn ignition off. With suspect sensor disconnected, measure resistance between HO2S HEATER GND terminal and VPWR terminal at HO2S wiring harness connector. If resistance is 3-30 ohms, go to next step. If resistance is not 3-30 ohms, replace HO2S sensor and repeat QUICK TEST.
  15. 35)  Leave ignition off and suspect sensor disconnected. Measure resistance between HO2S HEATER GND terminal at HO2S wiring harness connector and HO2S case. Measure resistance between HO2S HEATER GND terminal and SIG RTN terminal at HO2S wiring harness connector. Measure resistance between VPWR terminal at HO2S wiring harness connector and HO2S case. If each resistance measurement is more than 10,000 ohms, go to next step. If any resistance is 10,000 ohms or less, replace HO2S and repeat QUICK TEST.
  16. 36) Check For Short Circuit  Leave ignition off and sensor disconnected. Disconnect scan tester from DLC (if applicable). Disconnect PCM 104-pin connector. Inspect connector for damage and repair if necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between suspect sensor and test pins indicated as follows:
    • DTC P0135 (RF), test pin No. 93 and test pins No. 24, 91, 97 and 103.
    • DTC P0141 (RR), test pin No. 95 and test pins No. 24, 91, 97 and 103.
    • DTC P0155 (LR), test pin No. 94 and test pins No. 24, 91, 97 and 103.
    • DTC P0161 (LR), test pin No. 96 and test pins No. 24, 91, 97 and 103.

    If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short in circuit and repeat QUICK TEST.

  17. 37)  Leave ignition off and sensor disconnected. Measure resistance between HO2S HEATER GND terminal at HO2S wiring harness connector and appropriate test pin as follows:
    • Right front (or front) HO2S sensor; test pin No. 93.
    • Left front (or rear on 4.9L) HO2S sensor; test pin No. 94.
    • Right rear (or rear) HO2S sensor; test pin No. 95.
    • Left rear HO2S sensor; test pin No. 96.

    If resistance is 4 ohms or more, repair open circuit or excessive resistance in wiring harness and repeat QUICK TEST. If resistance is less than 4 ohms, replace PCM and repeat QUICK TEST.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 37) to step 40). No test procedures have been omitted.
  18. 40) DTC P1130, P1150, P1131, P1151, P1132 Or P1152: HO2S Not Switching  DTCs P1131 and P1151 indicate air/fuel ratio is correcting rich for an overly lean condition. DTCs P1132 and P1152 indicate air/fuel ratio is correcting lean for an overly rich condition. DTCs P1130 and P1150 indicate fuel system has reached maximum compensation and HO2S is not switching at the adaptive limits. Possible causes are as follows:
    • Fuel system malfunction.
    • EGR system malfunction.
    • Air intake or vacuum system leak.
    • Engine oil level too high.
    • Excessive internal engine wear.

    Inspect engine for obvious defects in specified systems. Repair or replace as necessary. If no faults are found, go to next step.

  19. 41) DTC P0171, P0172, P0174 Or P0175: HO2S Not Switching  DTCs P0171 and P0174 indicate air/fuel ratio is correcting rich for an overly lean condition. DTCs P0172 and P0175 indicate air/fuel ratio is correcting lean for an overly rich condition. Possible causes are as follows:
    • Fuel system malfunction.
    • EGR system malfunction.
    • Air intake or vacuum system leak.
    • Engine oil level too high.
    • Excessive internal engine wear.

    Inspect engine for obvious defects in specified systems. Repair or replace as necessary. If no faults are found, go to next step.

  20. 42) Perform KOER Self-Test  With ignition off, connect scan tester to DLC. Disconnect fuel vapor hose from intake manifold. Plug fitting at intake manifold. Start engine, and operate at 2000 RPM for one minute. Perform KOER self-test and proceed as follows:
    • If DTCs P1127, P1128 or P1129 are present, go to appropriate CIRCUIT TEST.
    • If DTCs P0131 or P0151 are present in continuous memory, go to step 27).
    • If DTCs P1131, P1130 or P1151, P1150 are present, go to step 43).
    • If DTCs P1130, P1132 or P1150, P1152 are present, go to step 49).

    If none of these DTCs are present, proceed as follows:

    • If diagnosing DTCs P1130, P1150, P1171, P1172, P1174 or P1175, go to step 52).
    • If diagnosing DTCs P1132 or P1152, go to CIRCUIT TEST HW , step 13).
    • If diagnosing any other DTCs, go to CIRCUIT TEST Z .

  21. 43)  Disconnect suspect HO2S. Turn ignition on. Using scan tool, access HO2S PID of suspect sensor. Connect jumper wire between HO2S SIG and VPWR circuit at HO2S harness connector. If spark occurs, remove jumper wire and go to step 47). If HO2S voltage is more than 1.3 volts, go to next step. If voltage is 1.3 volts or less, go to step 46).
  22. 44) Check Circuit Resistance  Turn ignition off. Connect PCM to breakout box. Measure resistance between battery ground terminal and SIG RTN terminal of HO2S harness connector. If resistance is less than 5 ohms, go to step 52). If resistance is 5 ohms or more, go to next step.
  23. 45)  Turn ignition off. Disconnect PCM from breakout box. Measure resistance between test pin No. 91 (SIG RTN) at breakout box and SIG RTN terminal of HO2S harness connector. If resistance is less than 5 ohms, replace PCM and repeat QUICK TEST. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST.
  24. 46) Check Resistance Of HO2S Ground Circuits  Turn ignition off. Install breakout box, leaving PCM disconnected. Disconnect suspect HO2S wiring harness connector. Inspect connector for damage and repair as necessary. Measure resistance between HO2S test pin at breakout box and HO2S terminal at sensor wiring harness connector. If resistance is less than 5 ohms, go to next step. If any resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST.
  25. 47) Check HO2S Circuit For Short To Ground  Turn ignition off. Leave breakout box installed and PCM disconnected. Disconnect HO2S. Measure resistance between HO2S SIG circuit test pin and test pins No. 24, 51, 77, 91 and 103 at breakout box. If all readings are 10,000 ohms or more, go to next step. If any reading is less than 10,000 ohms, repair short circuit and repeat QUICK TEST.
  26. 48) Check HO2S For Short To Ground  Ensure ignition is off and PCM is disconnected. Reconnect HO2S to wiring harness connector. Measure resistance between HO2S SIG RTN test pin and test pin No. 91 at breakout box. If resistance measurement is less than 10,000 ohms, replace HO2S and repeat QUICK TEST. If resistance is 10,000 ohms or more, replace PCM.
  27. 49) Check HO2S PID  Leave ignition off and HO2S disconnected. Turn ignition on. Using scan tool, access HO2S PID of suspect sensor. If HO2S PID voltage is more than 0.2 volts, go to next step. If HO2S voltage is 0.2 volts or less, go to step 51).
  28. 50) Check For Short To Power  Turn ignition off. Disconnect scan tester from DLC (if applicable). Disconnect PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair wiring as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Leave suspect HO2S disconnected. Measure resistance between HO2S terminal of wiring harness connector and following test pins at breakout box:
    • DTC P01130 and P01132; test pin No. 60 and test pins No. 71, 93 and 97.
    • DTC P01150 and P01152; test pin No. 87 and test pins No. 71, 94 and 97.

    If each resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST. If any resistance is 10,000 ohms or less, repair short to power and repeat QUICK TEST.

  29. 51)  Turn ignition off. Disconnect suspect HO2S. Turn ignition on. Using scan tool, access HO2S PID of suspect sensor. If HO2S voltage is more than 0.45 volts, replace HO2S and repeat QUICK TEST. If voltage is 0.45 volts or less, go to next step.
  30. 52) Check Fuel Pressure  Release fuel system pressure. With ignition off, install fuel pressure gauge. Ensure manifold vacuum is connected to fuel pressure regulator. Start engine and operate at 2500 RPM. If vehicle will not start, cycle key on and off. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel system pressure is as specified, go to next step. If fuel system pressure is not as specified, go to CIRCUIT TEST KN .
  31. 53) Check System Ability To Hold Fuel Pressure  With fuel pressure gauge installed, cycle ignition from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). If fuel pressure does not remain at specification for 60 seconds, go to step 4) under CIRCUIT TEST HC . If fuel pressure remains within 5 psi of highest fuel pressure reading for 60 seconds, proceed as follows:
    • For no-start vehicles, go to step 55).
    • For DTCs P1130, P01150, P0171, P0172, P0174 and P0175, go to step 54).
    • For HO2S DTCs displayed with misfire DTCs, go to step 56).
    • For all other DTCs, go to step 60).
  32. 54) Check Ability To Hold Fuel Pressure  With fuel pressure gauge installed, cycle ignition from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). Note fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure remains within 5 psi of original pressure for at least 10 seconds, go to step 56). If fuel pressure drops more than 5 psi, go to step 58).
  33. 55) Check Ability Of Injectors To Deliver Fuel  With fuel pressure gauge installed, cycle ignition from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). Note fuel pressure. Disconnect Inertia Fuel Switch (IFS). Crank engine for 5 seconds. If fuel pressure remains within 5 psi (34 kPa) of original pressure, reconnect IFS switch and go to next step. If fuel pressure drops more than 5 psi (34 kPa), repair fuel system as necessary. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article in this section.
  34. 56) Check Fuel Injector & Circuit Resistance  Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for damage or corrosion and repair as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure and record resistance between suspected fuel injector circuit test pin and test pin No. 71 and 97 at breakout box. Refer to FUEL INJECTOR INJ CIRCUIT IDENTIFICATION  table. Resistance should be 11-18 ohms. If resistance is not correct, go to next step. If resistance is correct, go to step 59).
    FUEL INJECTOR INJ CIRCUIT IDENTIFICATION

    Injector No. Test Pin No.
    1 75
    2 101
    3 74
    4 100
    5 (1) 73
    6 (1) 99
    7 (1) 72
    8 (1) 98
    9 (1) 68
    10 (1) 42
    (1) If equipped.
  35. 57) Check Resistance Of Fuel Injector Circuit  Turn ignition off. Disconnect suspect fuel injector wiring harness connector. Measure resistance between test pins No. 71 and 97 at breakout box and fuel injector VPWR terminal at wiring harness connector. Measure resistance between fuel injector signal test pin(s) at breakout box and same fuel injector circuit terminal at each fuel injector wiring harness connector. If each resistance is less than 5 ohms, go to next step. If each resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST.
  36. 58) Check Fuel Injector Circuit For Short To Power Or Ground  Turn ignition off. Disconnect suspect fuel injector wiring harness connector. Measure resistance between fuel injector test pin and test pins No. 24, 71, 97 and 103 at breakout box. Also, measure resistance between fuel injector test pin(s) at breakout box and chassis ground. If each resistance is 10,000 ohms or more, go to next step. If any resistance is less than 10,000 ohms, repair short circuit and repeat QUICK TEST.
  37. 59) Check Fuel Injector Drive Signal  With ignition off, connect PCM to breakout box. Connect non-powered 12-volt test light between suspect fuel injector and test pins No. 71 and 97. Crank or start engine. If test light glows dimly, go to next step. If test light does not glow dimly (no light/bright light), replace PCM and repeat QUICK TEST.
  38. 60) Check Fuel Injector Flow & Leakage  Turn ignition off. Remove breakout box. Reconnect PCM. Use Rotunda Injector Tester (113-00001) to flow test fuel injectors. If fuel injector flow or leakage rate is not okay, replace fuel injector, and repeat QUICK TEST. If flow rate for each fuel injector is okay, proceed as follows:
    • For DTCs P1131 and P1151, go to next step.
    • For DTCs P0171, P0174, P1130, and P1150, go to step 62).
    • For DTCs P1132 and P1152, go to step 65).
    • For DTCs P1172 and P1175, go to CIRCUIT TEST Z .
  39. 61) Check Secondary Air Injection  If vehicle is not equipped with secondary air injection, go to next step. Turn ignition off. Disconnect secondary air injection hoses. Plug air injection ports. With engine at operating temperature, perform KOER self-test. If DTC P1131 or P1151 are present, reconnect hose and go to next step. If specified DTCs are not present, go to step 7) under CIRCUIT TEST HM .
  40. 62)  Check air induction system for leaks or restrictions. Check PCV system for leaks or restrictions. Check vacuum hoses for damage and tight connection. Repair or replace as necessary. If no faults are found, go to next step.
  41. 63) Check Cylinder Compression  Using compression gauge, check cylinder compression. If cylinder compression is not okay, repair engine as necessary. Clear PCM memory and repeat QUICK TEST. If compression is okay, go to next step (DTCs P1130, P1150, P1131 and P1151) or step 65) (DTCs P1132 and P1152). If misfire DTCs are displayed with fuel control DTCs, go to CIRCUIT TEST HD , step 20).
  42. 64) Check HO2S Integrity  DTCs P0130, P0150, P0131, and P0151 indicate HO2S switches slow or doesn't switch, is always lean or fuel is at adaptive limit. Possible causes are as follows:
    • Moisture inside HO2S causing short to ground.
    • HO2S coated with contaminates.
    • HO2S circuit open or shorted to ground.

    Turn ignition off. Inspect HO2S and circuit for damage or contamination. Repair or replace HO2S or wiring as necessary. Start engine and operate at 2000 RPM for 3 minutes. Turn ignition off. Connect scan tool to DLC. Perform KOER self-test while monitoring HO2S voltage. If HO2S voltage is 0.5 volt or more at the end of test, go to step 70). If voltage is less than 0.5 volt, replace HO2S sensor and repeat QUICK TEST.

  43. 65) Perform KOER Self-Test  Start engine, and warm it to normal operating temperature. Turn ignition off. Disconnect suspect HO2S. Using a jumper wire, connect HO2S terminal of wiring harness connector to negative battery terminal. Perform KOER self-test. If DTC P1131 or P1151 is present, remove jumper wire and go to next step. If DTC P1131 or P1151 is not present, check PCM connector and service if necessary. If connector is okay, replace PCM. Repeat QUICK TEST.
  44. 66) HO2S Check  Leave HO2S disconnected. Connect DVOM between HO2S SIG terminal and SIG RTN terminal of HO2S wiring harness connector. Disconnect any vacuum hose from vacuum tree. Start engine and operate at 2000 RPM. If DVOM reads less than 0.4 volt within 30 seconds, go to step 70). If DVOM does not read as specified, replace HO2S and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 66) to step 70). No test procedures have been omitted.
  45. 70) Monitor HO2S PID  Connect scan tester to DLC. Start engine and allow to idle. Using scan tester, access HO2S PID. Observe HO2S PID while shaking and bending wiring harness between HO2S and PCM. If HO2S voltage stays at 0.45 volt, go to next step. If HO2S voltage is more than 0.45 volt or less than 0.45 volt, isolate fault and repair as necessary.
  46. 71) Monitor HO2S PID During Test Drive  Leave scan tester connected to DLC. Using an assistant, test drive vehicle under various conditions while observing HO2S PID. If HO2S voltage switches from about 0.4 to 0.6 volt, system is okay and testing is complete. If voltage does not switch, replace HO2S and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 71) to step 80). No test procedures have been omitted.
  47. 80) DTC P0136, P1137, P1138, P0156, P1157 & P1158  DTCs P0136 and P0156 indicate that output voltage of downstream HO2S is not within a functional window. If DTC P0136/P0156 is present, go to next step. If DTC P0136/P0156 is not present, go to step 82). KOER DTCs P1137, P1138, P1157 and P0158 indicate fuel control malfunction monitored as voltage change downstream HO2S. Possible causes are as follows:
    • Damaged wiring harness or connector.
    • Exhaust system leaks.
    • Contaminated or defective HO2S.

    Inspect for faults. Repair or replace as necessary. If no faults are found, go to next step.

  48. 81) Perform KOER Self-Test  Start engine, and operate at 2000 RPM for 3 minutes. With scan tester connected, perform KOER self-test. If DTCs P1137 P1138, P1157 or P1158 are present, go to next step. If specified DTCs are not present, fault is intermittent. Go to CIRCUIT TEST Z .
  49. 82) Check Exhaust System  Leaks in exhaust system can cause DTCs P0136 and P0156. Possible causes are as follows:
    • Incorrect HO2S torque.
    • Exhaust system leaks.

    Inspect entire exhaust system including catalyst and HO2S. Repair or replace as necessary. Clear PCM memory and repeat QUICK TEST. If not faults are present, go to next step.

  50. 83) Check HO2S Circuit For Short Circuit  Leave ignition off and suspect HO2S disconnected. Disconnect scan tester from DLC. Disconnect PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair circuit as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between HO2S test pin and test pins No. 24, 71, 90 (VREF), 91 (SIG RTN), 97 (VPWR), and 103 (PWR GND) at breakout box. Measure resistance between HO2S test pin and VPWR test pin at breakout box. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short circuit in wiring harness. Clear PCM memory. Drive vehicle for 5 miles and repeat QUICK TEST.
  51. 84) Check Ground Circuit Resistance  Leave ignition off and suspect HO2S disconnected. Measure resistance between HO2S SIG test pin at breakout box and HO2S SIG terminal at wiring harness connector. Measure resistance between SIG RTN test pin at breakout box and SIG RTN terminal at wiring harness connector. If resistance is 5 ohms or more, repair open circuit in wiring harness and repeat QUICK TEST. If resistance is less than 5 ohms, go to next step.
  52. 85) Check HO2S Circuit  Turn ignition off. Connect scan tester to DLC. Ensure suspect HO2S and PCM are connected. Turn ignition on. Access HO2S PID of suspect sensor. If voltage reading is 1.5 or more, go to step 88). If voltage is less than 1.5 volts, go to next step.
  53. 86) Check Circuit Resistance  Turn ignition off. Connect PCM to breakout box. Measure resistance between PWR GND test pin and SIG RTN test pin at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, replace PCM and repeat QUICK TEST.
  54. 87) Check HO2S PID  Leave ignition off and HO2S disconnected. Using jumper wire, connect VPWR and HO2S signal terminal of wiring harness connector. Turn ignition on. Using scan tool, access HO2S PID of suspect sensor. If HO2S PID voltage is more than 1.5 volts, replace HO2S. Clear PCM memory. Drive vehicle for 5 miles and repeat QUICK TEST. If HO2S PID voltage is 1.5 volts or less, replace PCM. Clear PCM memory. Drive vehicle for 5 miles and repeat QUICK TEST.
  55. 88) Check PCM Voltage  Leave suspect HO2S disconnected. Turn ignition on. Measure voltage between SIG RTN terminal at HO2S wiring harness connector and negative battery terminal. Measure voltage between HO2S SIG terminal at wiring harness connector and negative battery terminal. If voltage is 1.5 volts or more, replace PCM and repeat QUICK TEST. If voltage is less than 1.5 volts, replace HO2S and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 88) to step 100). No test procedures have been omitted.
  56. 100) KOER DTC P0127  DTC P0127 indicates that HO2S heater was not on during KOER self-test and testing of HO2S did not occur. Possible cause is cool exhaust system. Connect scan tester to DLC. Using scan tester, access all HO2S HEATER. If all PIDs indicate ON, repeat QUICK TEST. If any PIDs are off, operate engine until all PIDs are on; repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 100) to step 110). No test procedures have been omitted.
  57. 110) Check For Crossed HO2S Circuit  Turn ignition off. Disconnect suspect HO2S. Inspect connector for indication of crossed wires or incorrect installation. Repair or replace if necessary and repeat KOER self-test. If no faults are found, go to next step.
  58. 111)  Leave ignition off and suspect HO2S disconnected. Disconnect PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair circuit as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between suspect circuit terminal at wiring harness connector and corresponding test pin at breakout box. If resistance is less than 5 ohms, fault is intermittent and cannot be duplicated at this time. Repeat QUICK TEST to verify DTC is present. If resistance is 5 ohms or more, repair circuit. Clear PCM memory. Drive vehicle for 5 miles and repeat QUICK TEST.
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