Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.

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

HO2S and sensor connection.
Vacuum systems.
Fuel injector and/or fuel injector circuitry.
Powertrain Control Module (PCM).
Electrical circuits (HO2S, HO2S GND, INJ 1-8, VPWR and SIG RTN).

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:

Ignition system.
Faulty evaporative emission system.
EGR and/or PCV system.
Air intake system.
Engine oil contamination.
Fuel system.
Exhaust system leaks or restriction.
Engine cooling system.

CIRCUIT TEST ACRONYMS

Acronym	Definition
DLC	Data Link Connector
HO2S	Heated Oxygen Sensor
PID	Parameter Identification

Fig 1: Identifying HO2S Connector Terminals (Ranger)

Fig 2: Identifying Fuel Injector Connector Terminals (Ranger)

NOTE: Test procedure begins with step 10). No test procedures have been omitted.

10) DTC P0132, P0138, P0152 & P0158

These codes indicate that an overvoltage (more than 1.5 volts) has occurred in HO2S as follows:

DTC P0132 for right front HO2S.
DTC P0138 for left front HO2S.
DTC P0152 for right rear HO2S.
DTC P0158 for left rear HO2S.

Possible causes are as follows:

Signal shorted in wiring harness.
Faulty HO2S.
Faulty PCM.

With scan tester connected, turn ignition on. Access PID for fault code generated. If PID voltage is 1-4 volts, go to next step. If voltage is not 1-4 volts, fault is intermittent and cannot be duplicated at this time. Go to CIRCUIT TEST Z.

11) Check For Short In HO2S Wiring Harness

Turn ignition off. Disconnect suspect sensor. Disconnect PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between suspect sensor and test pins indicated as follows:

DTC P0132, test pin No. 60 and test pins No. 71, 93 and 97.
DTC P0138, test pin No. 35 and test pins No. 71, 95 and 97.
DTC P0152, test pin No. 87 and test pins No. 71, 94 and 97.
DTC P0158, test pin No. 61 and test pins No. 71, 96 and 97.

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.

12) Check Sensor For Internal Short

Turn ignition off. Disconnect suspect sensor. Connect scan tester to DLC. Turn ignition on. Access HO2S PID. If PID voltage is less than 0.2 volt, replace HO2S and repeat QUICK TEST. If PID voltage is 0.2 volt or more, replace PCM and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 20). No test procedures have been omitted.

20) DTC P0133 & P0153

This code indicates that response rate is below calibration in HO2S as follows:

DTC P0133 for right front HO2S.
DTC P0153 for left front 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. Scroll to Oxygen Sensor Test and enter. Scroll to Manufacturer Specific Test ID and enter. Scroll to Test ID: (41H) and enter. If measurement fault is 0.6 volt or more, fault cannot be duplicated or identified at this time and testing is complete. If measurement fault is less than 0.6 volt, go to next step.

21) 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. If none of these conditions are present, go to next step.

22) 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 dipstick and/or dipstick tube.

If any of these conditions are present, repair or replace as necessary. If none of these conditions are present, go to next step.

23) 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 SIG RTN 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.

24) 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.

25) Check HO2S For Short Circuit

Ensure ignition is off and PCM is disconnected. 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.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 27). No test procedures have been omitted.

27) DTC P0131 & P0151 - These DTCs are set when HO2S generates negative voltage. Possible causes are as follows:

Open or shorted circuit.
HO2S contaminated with water, fuel, etc.

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

28) Check HO2S For Short Circuit - Ensure ignition is 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 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.

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 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.

31) 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 more, go to next step. If voltage is less than 10.5 volts, repair VPWR circuit and repeat QUICK TEST.

32) 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, replace HO2S sensor and repeat QUICK TEST.

33) 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.

34) Leave ignition off and 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 and repeat QUICK TEST.

35) Leave ignition off and suspect sensor disconnected. Measure resistance between HO2S HEATER GND terminal at HO2S wiring harness connector HO2S case. If resistance is 10,000 ohms or more, go to next step. If resistance is less than 10,000 ohms, replace HO2S sensor and repeat QUICK TEST.

36) Check For Short Circuit - Leave ignition off and sensor disconnected. 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, 76, 91 and 103.
DTC P0141 (RR), test pin No. 95 and test pins No. 24, 76, 91 and 103.
DTC P0155 (LR), test pin No. 94 and test pins No. 24, 76, 91 and 103.
DTC P0161 (LR), test pin No. 96 and test pins No. 24, 76, 91 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.

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:

Left front HO2S sensor; test pin No. 94.
Right front HO2S sensor; test pin No. 93.
Left rear HO2S sensor; test pin No. 96.
Right rear HO2S sensor; test pin No. 95.

If resistance is 4 ohms or more, repair open circuit 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.

40) DTC P1130, P1150, P1131, P1151, P1132, P1152, P0171, P0172, P0174 Or P0175 : HO2S Not Switching

DTCs P1131, P1151, P1132 and P1152 indicate upstream HO2S not switching.

DTCs P1130 and P1150 indicate system is not switching at the adaptive limits.

DTCs P0171, P0172, P0174 and P0175 indicate system is continuously at the adaptive limits.

Possible causes are as follows:

Engine oil level too high.
Excessive internal engine wear.
Fault in secondary ignition.

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

41) Perform KOER Self-Test

Start engine, and warm it to normal operating temperature. With scan tester connected, perform KOER self-test. If any of the codes in step 40) are present, go to step 42). If none of the codes in step 40) are present, fault is intermittent. Go to CIRCUIT TEST Z.

42) 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 allow to idle or cycle key on and off if vehicle will not start. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, repair as necessary.

43) 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 remains within 5 psi of highest fuel pressure reading for 60 seconds, go to step 45) for DTCs P1130, P01150, P0171, P0172, P0174 and P0175 or go to step 50) for all others. If fuel pressure does not remain at specification for 60 seconds, repair fuel system as necessary.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 43) to step 45). No test procedures have been omitted.

45) 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 of original pressure, go to next step. If fuel pressure drops more than 5 psi, repair fuel system as necessary.

46) 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 correct but vehicle will not start, go to step 49). If resistance is correct, go to next step.

FUEL INJECTOR INJ CIRCUIT IDENTIFICATION

Injector	Test Pin No.	Wire Color
No. 1	75	Tan
No. 2	101	White
No. 3	74	Brown/Yellow
No. 4	100	Brown/Blue
No. 5	73	Tan/Black
No. 6	99	Green/Orange

47) Check Continuity 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. See Fig 1 or Fig 2 . 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. Reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

48) 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, 76, 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 each resistance is less than 10,000 ohms, repair short. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

49) 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. Reconnect all components, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

50) 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, clean fuel injectors, and repeat QUICK TEST. If flow rate for each fuel injector is okay, go to CIRCUIT TEST Z,

(DTCs P1171, P1172, P1174 and P1175) or next step for all others.

51) Using compression gauge, check cylinder compression. If compression is okay, go to next step (DTCs P1130, P1150, P1131 and P1151) or step 57) (DTCs P1132 and P1152). If cylinder compression is not okay, repair engine as necessary. Clear PCM memory and repeat QUICK TEST.

52) 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 2 minutes. Turn ignition off. Connect scan tool to DLC and perform KOER self-test. If trouble codes are present, go to next step. If no trouble codes are present, faults cannot be duplicated or identified at this time. Testing is complete.

53) Check HO2S Ability To Generate Correct Voltage

Warm engine to normal operating temperature. Operate engine at 2000 RPM for 2 minutes. Perform KOER self-test while monitoring HO2S voltage. If voltage is 0.5 volt or more at the end of test, go to next step. If voltage is less than 0.5 volt, replace HO2S sensor and repeat QUICK TEST.

54) Check Continuity 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. Also, measure resistance between test pin No. 91 and SIG RTN terminal at HO2S sensor vehicle wiring harness connector. If each resistance is less than 5 ohms, go to next step. If any resistance is 5 ohms or more, repair open circuit. Remove breakout box, and reconnect all components. Drive vehicle for 5 minutes at 55 MPH. Repeat QUICK TEST.

55) Check HO2S Circuit For Short To Ground

Turn ignition off. Leave breakout box installed and PCM disconnected. Disconnect HO2S. Measure resistance between HO2S circuit test pin and test pins No. 24, 51 76, 77 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. Remove breakout box and reconnect all components. Drive vehicle at 55 MPH for 5 minutes and repeat QUICK TEST.

56) Check HO2S For Short To Ground

Ensure ignition is off and PCM is disconnected. Connect HO2S to wiring harness connector. Measure resistance between HO2S test pin and test pin No. 91 at breakout box. Measure resistance between HO2S test pin and test pins No. 24, 76 and 103 at breakout box. If any resistance measurement is less than 10,000 ohms, replace HO2S. Remove breakout box and reconnect all components. Drive vehicle for 5 miles at 55 MPH and repeat QUICK TEST. If resistance is 10,000 ohms or more, perform following procedure as applicable:

For DTCs P1130 and P1150, go to next step.
For Continuous Memory DTCs P1131 and P1151, go to step 62).
For KOER codes P1131 and P1151, replace PCM.

57) Perform KOER Self-Test

Start engine, and warm it to normal operating temperature. With scan tester connected, perform KOER self-test. If DTCs P1132 and P1152 are present, go to next step. If codes are not present, fault is intermittent. Go to CIRCUIT TEST Z.

58) Check For HO2S Short To Power

DTCs P1130, P1150 and/or P1132, P1152 indicate HO2S is always rich. Possible causes are as follows:

Moisture inside HO2S wiring harness connector.
HO2S circuit shorted to power.

Turn ignition off. With scan tool connected, access PID for code generated. If 1.0-4.0 volts are present, go to next step. If 1.0-4.0 volts are not present, go to step 61).

59) Check For Short To Power

Turn ignition off. 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, 93 and 97.

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

60) Leave ignition off and HO2S disconnected. Remove breakout box and reconnect PCM. Using scan tool, access HO2S PID of suspect sensor. If HO2S voltage is less than 0.2 volt, replace HO2S sensor and repeat QUICK TEST. If HO2S voltage is 0.2 volts or more, replace PCM and repeat QUICK TEST.

61) Attempt To Generate DTC P1131 or P1151

Leave ignition off and HO2S disconnected. 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, replace PCM and repeat QUICK TEST.

62) HO2S Check

Connect DVOM between HO2S terminal and SIG RTN terminal of wiring harness connector. Disconnect 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 62) to step 70). No test procedures have been omitted.

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 and repair as necessary.

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.

80) DTC P0136 & P0156

DTCs P0136 and P0156 indicate that output voltage of downstream HO2S is within a functional window. 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.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 80) to step 82). No test procedures have been omitted.

82) Check For Crossed HO2S Circuit

Turn ignition off. Disconnect suspect HO2S. Perform KOER self-test. If trouble code corresponding to disconnected HO2S is present, circuit is not crossed; go to next step. If trouble code corresponding to disconnected HO2S is not present, check for crossed wires. Repair as necessary and repeat KOER self-test.

83) Check HO2S Circuit For Short Circuit

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 HO2S test pin and test pins No. 24, 76, 103 (PWR GND), 71, 97 (VPWR), 90 (VREF) and 91 (SIG RTN) 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.

84) Check Ground Circuit Continuity

Leave ignition off and suspect HO2S disconnected. Measure resistance between HO2S test pin at breakout box and HO2S 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. Drive vehicle for 5 miles and repeat QUICK TEST. If resistance is less than 5 ohms, go to next step.

85) Check HO2S Circuit Continuity

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 87). If voltage is less than 1.5 volts, go to next step.

86) Check PCM Ground Circuit Continuity

Turn ignition off. Connect PCM to breakout box. Disconnect vehicle wiring harness from breakout box. Measure resistance between test pin No. 91 and test pins No. 24, 76 and 103 at breakout box. If resistance is less than 5 ohms, replace HO2S. Drive vehicle for 5 miles and repeat QUICK TEST. If resistance is 5 ohms or more, replace PCM. Drive vehicle for 5 miles and repeat QUICK TEST.

87) Check PCM Voltage

Leave suspect HO2S disconnected. Turn ignition on. Measure voltage between SIG RTN terminal at wiring harness connector and negative battery terminal. Measure voltage between HO2S SIGNAL terminal at wiring harness connector and negative battery terminal. If voltage is 1.5 volts or more, replace PCM. Drive vehicle for 5 miles and repeat QUICK TEST. If voltage is less than 1.5 volts, replace HO2S. Drive vehicle for 5 miles and repeat QUICK TEST.