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Home >> Mazda >> 1999 >> B2500 SX, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Engine Controls - Self-Diagnostics - EEC-V - 6.8L (99S E Series & 99S F350 To F550)) >> System Tests >> Test Ha: Natural Gas Fuel Control >> Diagnostic Aids

Diagnostic Aids

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Perform this test when directed by QUICK TEST or if directed by other test procedures. This test is used to diagnose:

WARNING: Fuel system remains under high pressure even when engine is not running. To avoid injury, release fuel pressure before disconnecting any fuel system hose or component. See appropriate REMOVAL, OVERHAUL & INSTALLATION article.
HO2S TEST PIN IDENTIFICATION(1)

HO2S HO2S SIG PCM Pin No. HO2S HTR PCM Pin No.
Left Front 87 94
Left Rear 61 96
Right Front 60 93
Right Rear 35 95
(1) SIG RTN circuit is PCM connector pin No. 91. VPWR circuit is PCM connector pin No. 71.
NOTE: Test procedure begins with step 30). No test procedures have been omitted.

  1. 30) DTCs 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 volts. HO2S DTC identification is as follows:
    • DTC P0135 is for right front HO2S.
    • DTC P0141 is for right rear HO2S.
    • DTC P0155 is for left front HO2S.
    • DTC P0161 is for left rear HO2S.

    Possible causes are:

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

    Ensure battery is fully charged. Inspect HO2S connectors for loose, damaged or corroded terminals. Repair as necessary. If HO2S connectors are okay, go to next step.

    NOTE: HO2S may be displayed on scan tool as O2S.

  2. 31) Perform KOEO Self-Test

    Start engine and operate at 2000 RPM for 5 minutes. Turn ignition off. Perform KOEO ON-DEMAND SELF-TEST . If DTC P0135, P0141, P0155 or P0161 are present, go to next step. If specified DTCs are not present, fault may be intermittent. Go to TEST Z .

  3. 32) Check For Voltage At HO2S Heater Wiring Harness Connector

    Turn ignition off. Disconnect suspect HO2S connector. Turn ignition on. Measure voltage between SIG RTN and VPWR terminals at HO2S wiring harness connector. See Fig 1. If voltage is 10.5 volts or less, go to next step. If voltage is more than 10.5 volts, go to step  34).
    Fig 1: Identifying HO2S Connector Terminals
    G95D35975Courtesy of FORD MOTOR CO.

  4. 33) Check For Open Circuit

    Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between VPWR terminal at HO2S wiring harness connector and PCM connector pin No. 71. 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 VPWR circuit.

  5. 34) Check HO2S Heater Circuit

    Turn ignition off. Measure resistance between HO2S HEATER GND terminal and VPWR terminal at HO2S. If resistance is 3-30 ohms, go to next step. If resistance is not 3-30 ohms, replace HO2S sensor.

  6. 35) Check For HO2S Case Short

    Measure resistance between HO2S HEATER GND terminal at HO2S and HO2S case. Also measure resistance between VPWR terminal at HO2S and HO2S case. If both resistance readings are more than 10,000 ohms, go to next step. If any resistance is 10,000 ohms or less, replace HO2S.

  7. 36) Check For Short Circuit

    Disconnect scan tool from DLC. Measure resistance between PCM connector pins as follows:
    • DTC P0135 (RF), pin No. 93 and pins No. 71, 91 and 103.
    • DTC P0141 (RR), pin No. 95 and pins No. 71, 91 and 103.
    • DTC P0155 (LF), pin No. 94 and pins No. 71, 91 and 103.
    • DTC P0161 (LR), pin No. 96 and pins No. 71, 91 and 103.

    If all resistance readings are more than 10,000 ohms, go to next step. If any resistance reading is 10,000 ohms or less, repair short circuit.

  8. 37) Check For Open Circuit

    Measure resistance between HO2S HEATER GND terminal at suspect HO2S wiring harness connector and appropriate HO2S HTR pin at PCM connector as follows:
    • Right front HO2S; pin No. 93.
    • Left front HO2S; pin No. 94.
    • Right rear HO2S; pin No. 95.
    • Left rear HO2S; pin No. 96.

    If resistance is 4 ohms or more, repair open circuit or excessive resistance in HO2S wiring harness. If resistance is less than 4 ohms, wiring harness is okay. Replace PCM.

    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.

  9. 40) DTCs P1130, P1131, P1132, P1150, P1151 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:
    • Fuel system malfunction.
    • Secondary ignition system malfunction.
    • Air intake or vacuum system leak.
    • Exhaust leak near HO2S.
    • Incorrect cam timing.
    • Restricted air cleaner.
    • Excessive internal engine wear.

    Inspect engine for obvious defects in specified systems. Repair as necessary. If no faults are found, go to step  42).

  10. 41) DTC P0171, P0172, P0174 Or P0175

    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:
    • Fuel system malfunction.
    • Secondary ignition system malfunction.
    • Air intake or vacuum system leak.
    • Exhaust leak near HO2S.
    • Incorrect cam timing.
    • Restricted air cleaner.
    • Excessive internal engine wear.
    • Ran out of fuel.

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

  11. 42) Perform KOER Self-Test

    Perform KOER ON-DEMAND SELF-TEST  and proceed as follows:
    • If DTC P0131, P0132, P0151 or P0152 is present, go to next step. If none of these DTCs are present, proceed as follows:
    • If diagnosing DTC P1130, P1150, P1171, P1172, P1174 or P1175, go to next step.
    • If diagnosing any other DTCs, fault may be intermittent. Go to TEST Z .

  12. 43) Check Fuel Pressure

    Turn ignition off. Connect fuel pressure gauge to Schrader valve located on fuel rail. Observe fuel pressure gauge. Turn ignition on and note fuel pressure reading. Start engine and allow to idle. Note fuel pressure reading. Increase engine speed to 2500 RPM for one minute. Note fuel pressure reading. If fuel pressure readings are 80-120 psi (552-827 kPa), go to next step. If fuel pressure readings are not 80-120 psi (552-827 kPa), go to TEST HB .

  13. 44) Check System Ability To Hold Fuel Pressure

    With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 2 times to pressurize fuel system (DO NOT start engine). If fuel pressure does not remain within 10 psi (69 kPa) of pressure reading for at least 2 minutes, go to TEST HB . If fuel pressure remains within 10 psi (69 kPa) of highest fuel pressure reading for 2 minutes, proceed as follows:
    • For no-start vehicles, go to next step.
    • For DTCs P1130, P1150, P0171 P0172, P0174 and P0175, go to next step.
    • For all other DTCs, go to step  62).

  14. 45) Check For Fuel System Stability

    With fuel pressure gauge installed, cycle ignition from OFF to ON (DO NOT start engine). Note fuel pressure. If fuel pressure drops more than 10 psi within 10 seconds, go to step  56). If fuel pressure remains within 10 psi of original pressure for at least 10 seconds, proceed as follows:
    • For no-start vehicles, go to next step.
    • For DTCs P1130, P1150, P0171 and P0174, go to step  55).

  15. 46) Check Ability Of Injectors To Deliver Fuel

    With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 2 times to pressurize fuel system (DO NOT start engine). Note fuel pressure. Disconnect Inertia Fuel Shutoff (IFS) switch. Crank engine for 10 seconds. If fuel pressure remains within 20 psi (137 kPa) of original pressure, remove fuel pressure gauge and reconnect IFS switch. Go to next step. If fuel pressure drops more than 20 psi (137 kPa), repair fuel system as necessary.

  16. 47) Check For VREF At NG Module

    Turn ignition off. Disconnect PCM connector. Locate NG module 60-pin connector. See NATURAL GAS MODULE LOCATION  table. Turn ignition on. Measure voltage between NG module connector pins No. 26 (VREF) and 46 (SIG RTN). If voltage is 4-6 volts, go to next step (no-start condition) or step  57) (except no-start conditions). If voltage is not 4-6 volts, go to step  50).
    NATURAL GAS MODULE LOCATION

    Application Location
    Crown Victoria Front Of Radiator Support
    Econoline In Left Side Of Engine Compartment, On Inner Fender
    F150 & F250 In Front Of Engine
    Fig 2: Identifying NG Module Circuits & Connector Terminals
    G95C35974Courtesy of FORD MOTOR CO.

  17. 48) Check For Open PWR GND Circuit

    Turn ignition off. Disconnect NG module 60-pin connector. Measure resistance between NG module connector pin No. 46 (SIG RTN) and negative battery terminal. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit.

  18. 49) Check For Open Circuit In NG Module

    Measure resistance between NG module pin No. 46 (SIG RTN) and No. 60 (GND). If resistance is less than 5 ohms, go to  TEST A, step 6). If resistance is 5 ohms or more, replace NG module.

  19. 50) Verify Voltage Reading

    If voltage in step  47) was less than 6 volts or less, go to next step. If voltage was more than 6 volts, go to step  55).

  20. 51) Check Battery Voltage

    Measure voltage across battery terminals. If voltage is 10.5 volts or less, check charging system and battery. Repair as necessary. If voltage is more than 10.5 volts, go to next step.

  21. 52) Check For Power At NG Module

    Turn ignition on. Measure voltage between NG module connector pins No. 57 (VPWR) and No. 60 (PWR GND). If voltage is 10.5 volts or less, go to next step. If voltage is more than 10.5 volts, go to step  54).

  22. 53) Check VPWR Voltage

    Measure voltage between negative battery terminal and NG module connector pin No. 57 (VPWR). If voltage is 10.5 volts or less, repair open in VPWR circuit. If voltage is more than 10.5 volts, repair open in PWR GND circuit.

  23. 54) Check Voltage To Fuel Tank Pressure Sensor

    Turn ignition off. Disconnect Fuel Tank Pressure (FTP) sensor connector. See FUEL TANK PRESSURE SENSOR LOCATION  table. Turn ignition on. Measure voltage between SIG RTN terminal and VREF terminal at FTP sensor wiring harness connector. See Fig 3. If voltage is 4-6 volts, replace FTP sensor. If voltage is not 4-6 volts, go to next step.
    FUEL TANK PRESSURE SENSOR LOCATION

    Application Location
    Crown Victoria On Upper Fuel Tank Assembly
    Econoline Under Left Center Of Vehicle
    Pickup Part Of Fuel Pump Assembly
    Fig 3: Identifying FTP Connector Terminals
    G99J02758Courtesy of FORD MOTOR CO.

  24. 55) Check For VREF Short To Power

    Ensure NG module is disconnected. Turn ignition on. Measure voltage between NG module connector pins No. 26 (VREF) and No. 60 (PWR GND). If voltage is less than one volt, replace NG module. If voltage is one volt or more, repair short to power in VREF circuit.

  25. 56) Check For VREF Short To Ground

    Turn ignition off. Measure resistance between NG module connector pin No. 26 (VREF) and pins No. 40, 46 and 60. If all resistance readings are more than 10,000 ohms, replace NG module. If any resistance reading is 10,000 ohms or less, repair short to ground.

  26. 57) Check Resistance Of Injectors & Related Circuits

    Leave ignition off and NG module disconnected. Measure resistance between suspect fuel injector pin and pin No. 37 or 57 at NG module connector. See NG MODULE FUEL INJECTOR PIN IDENTIFICATION  table. If resistance is 3-6 ohms, go to step  60). If resistance is not 3-6 ohms, go to next step.
    NG MODULE FUEL INJECTOR PIN IDENTIFICATION

    Cylinder No. NG Module Pin No.
    1 58
    2 59
    3 39
    4 35
    5 33
    6 42
    7 53
    8 54

  27. 58) Check Fuel Injector Harness Resistance

    Disconnect suspect fuel injector connector. Measure resistance of fuel injector circuit between suspect fuel injector pin at NG module connector and appropriate fuel injector wiring harness connector. See NG MODULE FUEL INJECTOR PIN IDENTIFICATION  table. Also measure resistance between NG module pin No. 37 or 57 and Red wire (VPWR) at suspect fuel injector wiring harness connector. If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open circuit.

  28. 59) Check Injector Harness For Short To Power Or Ground

    Disconnect scan tool from DLC. Ensure suspect fuel injector is disconnected. Measure resistance between suspect fuel injector pin and pins No. 37, 57, 40 and 60 at NG module connector. If any resistance reading is 10,000 ohms or less, repair short circuit. If all resistance readings are more than 10,000 ohms, go to step  61) if DTC P0172 or P0175 is present or replace damaged injector(s) if DTC P0172 or P0175 is not present.

  29. 60) Check Injector Driver Signal At NG Module

    Ensure ignition is off. Connect NG module connector. Connect test light between suspect fuel injector wiring harness connector terminals. While cranking engine, observe test light. If test light does not glow dimly (no light or continuous bright light) while cranking or running engine, go to next step. If test light glows dimly, PCM and NG module circuits are okay. If vehicle is a no-start, go to TROUBLE SHOOTING - NO CODES - EEC-V article. If vehicle starts, go to step  64).

  30. 61) Check PCM Injector Harness Circuit

    Ensure ignition is off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect NG module 60-pin connector. Measure resistance between PCM connector pin No. 71 and pin No. 37 or 57 at NG module connector. Also measure resistance of fuel injector circuits between PCM connector and NG module connector. See PCM OUTPUT TO NG MODULE INPUT TEST PINS  table. If all resistance reading are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open circuit.
    PCM OUTPUT TO NG MODULE INPUT TEST PINS

    Cylinder No. PCM Pin No. NG Module Pin No.
    1 75 3
    2 101 4
    3 74 5
    4 100 23
    5 73 24
    6 99 25
    7 72 43
    8 98 44

  31. 62) Check PCM Injector Harness For Short Circuit

    Measure resistance between NG module connector fuel injector pin(s) (No. 3, 4, 5, 23, 24, 25, 43 and/or 44) and pins No. 37, 40, 57 and 60. See PCM OUTPUT TO NG MODULE INPUT TEST PINS  table. Also measure resistance between PCM connector fuel injector pin(s) (No. 75, 101, 74, 100, 73, 99, 72 and/or 98) and pins No. 71 and 103. See PCM OUTPUT TO NG MODULE INPUT TEST PINS table. If all resistance readings are more than 10,000 ohms, go to next step. If any resistance reading is 10,000 ohms or less, repair short circuit.

  32. 63) Check Injector Driver Signal At PCM

    Ensure ignition is off. Connect PCM connector. Ensure NG module is disconnected. While cranking engine, connect test light between NG module connector pin No. 57 (VPWR) and pins No. 3, 4, 5, 23, 24, 25 and 44. If test light glows dimly while cranking and engine will not start, replace NG module. If test light glows dimly while cranking or running engine but engine runs rough, go to TROUBLE SHOOTING - NO CODES - EEC-V article and diagnose by symptom. If test light does not glow dimly while cranking or running engine, replace PCM.

  33. 64) Check Fuel Injector Flow & Leakage

    Turn ignition off. Reconnect all connectors. Use Rotunda injector tester from Fuel Tester Kit (113-00114) to flow test fuel injectors. Follow injector tester instructions. If fuel injector flow or leakage rate is not okay, replace defective fuel injector(s). If flow rate for each fuel injector is okay, proceed as follows:
    • For DTCs P0171, P0172, P0174 and P0175, fault is intermittent. Go to TEST Z .
    • For DTCs P1130 and P1150, go to step  66).
    • For all other DTCs, go to next step.

  34. 65) Check Cylinder Compression

    Using compression gauge, check cylinder compression. If cylinder compression is not okay, repair engine as necessary. If compression is okay, go to next step (DTCs P1130, P1131, P1150 and P1151) or step  71) (DTCs P1132 and P1152).

  35. 66) Check HO2S Integrity

    DTCs P1130, P1150, P1131, and P1151 indicate HO2S switches slow or doesn't switch, is always lean or fuel is at adaptive limit. Possible causes are:
    • Moisture inside HO2S causing short to ground.
    • HO2S coated with contaminates.
    • HO2S circuit open or shorted to ground.

    Turn ignition off. Inspect HO2S and wiring harness for damage and contamination from oil, water, etc. Repair as necessary. If no visible problems are found, start engine and operate at 2000 RPM for 2 minutes. Turn ignition off. Using scan tool, perform KOER ON-DEMAND SELF-TEST . If DTC P1131 or P1151 is present, go to next step. If DTC P1131 or P1151 is not present, HO2S system is functioning properly at this time. Faults cannot be duplicated or identified at this time. Testing is complete.

  36. 67) Check HO2S Ability To Generate Correct Voltage

    Turn ignition off. Disconnect suspect HO2S connector. Using DVOM, measure voltage between HO2S SIG terminal and SIG RTN terminal at HO2S wiring harness connector. See Fig 1. Start engine and operate at 2000 RPM for 2 minutes. Perform KOER ON-DEMAND SELF-TEST  while monitoring voltage. If voltage is more than .5 volt during or at end of test, go to next step. If voltage stays at .5 volt or less during test, replace HO2S sensor.

  37. 68) Check Resistance Of HO2S Ground Circuits

    Turn ignition off. Disconnect PCM connector. Disconnect suspect HO2S connector. Inspect both ends of connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance of between appropriate HO2S SIGNAL pin at PCM connector and HO2S SIGNAL terminal at HO2S wiring harness connector. HO2S pin identification is as follows:
    • Left Front HO2S; PCM connector pin No. 87.
    • Right Front HO2S; PCM connector pin No. 60.

    Also measure resistance between PCM connector pin No. 91 and SIG RTN terminal at HO2S wiring harness connector. If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open circuit.

  38. 69) Check HO2S Circuit For Short To Ground

    Measure resistance between appropriate HO2S SIG circuit pin at PCM connector and negative battery terminal. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short to ground.

  39. 70) Check HO2S For Short To Ground

    Measure resistance between appropriate HO2S SIGNAL pin and pins No. 91 and 103 at PCM connector. If any resistance reading is 10,000 ohms or less, replace HO2S. If both resistance readings are more than is 10,000 ohms, proceed as follows:
    • For DTCs P1130 and P1150, go to next step.
    • For Continuous Memory DTCs P1131 and P1151, go to step  76).
    • For KOER DTCs P1131 and P1151, replace PCM.

  40. 71) Perform KOER Self-Test

    Start engine, and warm it to normal operating temperature. With scan tool connected, perform KOER ON-DEMAND SELF-TEST . If DTC P1132 or P1152 is present, go to next step. If DTC P1132 or P1152 is not present, fault is intermittent. Go to TEST Z .

  41. 72) Check For HO2S Short To Power

    DTCs P1130, P1150 and/or P1132, P1152 indicate HO2S is always rich. DTCs P1130 and P1132 are for right front HO2S. DTCs P1150 and P1152 are for left front HO2S. Possible causes are:
    • Moisture inside HO2S wiring harness connector.
    • HO2S circuit shorted to power.
    NOTE: HO2S may be displayed on scan tool as O2S.

    Turn ignition on. Using scan tool, select appropriate HO2S PID for DTC generated. If PID voltage is 1-4 volts, go to next step. If PID voltage is not 1-4 volts, go to step  75).

    • PID for DTC P1130 and P1132 is HO2S-11.
    • PID for DTC P1150 and P1152 is HO2S-21.

  42. 73) Check For Short To Power

    Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect suspect HO2S connector. Disconnect scan tool from DLC. For DTCs P1130 and P1132, measure resistance between PCM connector pins No. 60 and 71. For DTCs P1150 and P1152, measure resistance between PCM connector pins No. 87 and 71. If both resistance readings are more than 10,000 ohms, reconnect PCM connector and go to next step. If any resistance reading is 10,000 ohms or less, repair short to power.

  43. 74) Check HO2S Signal

    Ensure suspect HO2S is disconnected. Turn ignition on. Using scan tool, select HO2S PID for DTC generated. If PID voltage is less than .2 volt, replace HO2S. If PID voltage is .2 volt or more, replace PCM.

  44. 75) Attempt To Generate DTC P1131 & P1151

    Connect a jumper wire between HO2S SIGNAL terminal at HO2S wiring harness connector and negative battery terminal. Perform KOER ON-DEMAND 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 terminals and repair as necessary. If PCM connector is okay, replace PCM.

  45. 76) HO2S Check

    Connect DVOM between HO2S SIGNAL terminal and SIG RTN terminal at HO2S wiring harness connector. Disconnect any vacuum hose from vacuum tree. Start engine and operate at 2000 RPM. If DVOM voltage is less than .4 volt within 30 seconds, reconnect vacuum hose and reconnect all connectors. Go to next step. If DVOM voltage is not less than .4 volt, replace HO2S.

  46. 77) Monitor HO2S PID

    Start engine and allow to idle. Using scan tool, select HO2S PID for suspect HO2S. Observe PID voltage while wiggling and bending wiring harness between HO2S and PCM. If PID voltage stays high (more than .45 volt) or stays low (less than .45 volt), isolate cause of lack of HO2S switches. Repair as necessary. If PID voltage switches, go to next step.

  47. 78) Monitor HO2S PID During Test Drive

    Leave scan tool connected to DLC. Using an assistant, test drive vehicle under various conditions while observing HO2S PID voltage. If PID voltage switches from about .4 to .6 volt, system is okay and testing is complete. If voltage does not switch from about .4 to .6 volt, replace HO2S.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 78) to step 80). No test procedures have been omitted.

  48. 80) KOER DTCs P1137, P1138, P1157 & P1158

    These DTCs indicate lack of HO2S switching. Possible causes are:
    • Damaged wiring harness or connector.
    • Exhaust system leaks.
    • Contaminated or defective HO2S.
    • Faulty PCM.

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

  49. 81) Check Exhaust System

    Leaks in exhaust system between engine and end of catalytic converter can cause DTCs P1137, P1138, P1157 and P1158 to set. Possible causes are:
    • Incorrect HO2S torque.
    • Exhaust system leaks.

    Inspect entire exhaust system including catalyst and HO2S. Repair as necessary. If no faults are present, go to next step.

  50. 82) Check HO2S Circuit

    Turn ignition off. Connect scan tool to DLC. Ensure suspect HO2S and PCM are connected. Turn ignition on. Using scan tool, select appropriate HO2S PID for DTC generated. If PID voltage is more than 1.6 volts, replace HO2S. If PID voltage is 1.6 volts or less, go to next step.
    • PID for DTC P1137 and P1138 is HO2S-12.
    • PID for DTC P1157 and P1158 is HO2S-22.

  51. 83) Check HO2S Circuit For Short Circuit

    Disconnect scan tool from DLC. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM connector pin No. 91 (SIG RTN) and appropriate HO2S SIGNAL pin as follows:
    • HO2S-12 (right rear HO2S), PCM connector pin No. 35.
    • HO2S-22 (left rear HO2S), PCM connector pin No. 61.

    Also measure resistance between appropriate HO2S SIGNAL pin and pins No. 71 (VPWR), 90 (VREF) and 103 (PWR GND) at PCM connector. If all resistance readings are more than 10,000 ohms, go to next step. If any resistance reading is 10,000 ohms or less, repair short circuit.

  52. 84) Check Ground Circuit Continuity

    Disconnect suspect HO2S connector. Measure resistance between appropriate HO2S SIGNAL pin at PCM connector and HO2S SIGNAL terminal at suspect HO2S wiring harness connector. Also measure resistance between PCM connector pin No. 91 and SIG RTN terminal at suspect HO2S wiring harness connector. If any resistance reading is 5 ohms or more, repair open circuit. If both resistance readings are less than 5 ohms, replace PCM.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 84) to step 90). No test procedures have been omitted:

  53. 90) 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 tool to DLC. Using scan tool, select HTR-11, HTR-12, HTR-21 and HTR-22 HO2S heater PIDs from PID/DATA monitor menu. If all PIDs indicate ON, repeat KOER ON-DEMAND SELF-TEST . If any PID indicates OFF, operate engine until both PIDs are on. Repeat KOER ON-DEMAND SELF-TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 90) to step 100). No test procedures have been omitted.

  54. 100) KOER P1128 & P1129

    These DTCs indicate that during KOER self-test, one or both HO2S signals were crossed from bank to bank. DTC P1128 refers to HO2S in front of converter. DTC P1129 refers to HO2S behind converter. Possible causes for these faults are:
    • Crossed HO2S connectors.
    • Crossed HO2S wiring at HO2S connector.
    • Crossed HO2S wiring at PCM connector.

    Turn ignition off. Disconnect suspect HO2S. Inspect connector for indication of crossed wires or incorrect installation. Repair as necessary. If no faults are found, go to next step.

  55. 101) Verify Proper HO2S SIG Pin Location

    Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect both suspect HO2S connectors. HO2S DTC identification is as follows:
    • DTC P1128 is for left front HO2S and right front HO2S.
    • DTC P1129 is for left rear HO2S and right rear HO2S.

    Measure resistance between HO2S SIGNAL terminal at suspect HO2S wiring harness connector and appropriate HO2S SIG pin at PCM connector as follows:

    • Left Front HO2S; PCM connector pin No. 87.
    • Right Front HO2S; PCM connector pin No. 60.
    • Left Rear HO2S; PCM connector pin No. 61.
    • Right Rear HO2S; PCM connector pin No. 35.

    If all resistance readings are less than 5 ohms, fault is intermittent and cannot be duplicated at this time. If any resistance reading is 5 ohms or more, HO2S wiring is crossed. Recheck all HO2S wiring pin locations at PCM and HO2S connectors. Repair as necessary.

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