Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. (Fuel-contaminated engine oil may affect Codes 136, 137, 139, 144, 171, 172, 173, 175, 176 and 177. If fuel-contaminated engine oil is suspected, remove PCV valve from valve cover and repeat QUICK TEST  ). If problem is corrected, change engine oil and filter. Only use this test to diagnose:

• 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).

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.
• Intake, supercharger, or charge air cooler leaks.
• Exhaust system leaks or restriction.
• Electrical system.
• Secondary air injection system.
• Engine cooling system.
  Fig 1: Identifying Fuel Injector & HO2S Connector Terminals

  
  INDIVIDUAL INJECTOR RESISTANCE
  
  

  Engine	Ohms
  Mark VIII	11-18

  TEST PIN WIRE COLOR ID
  
  

  Application	Test Pin No.	Wire Color
  HO2S-1	44	Gray/Light Blue
  HO2S-2	43	Red/Black
  HO2S-GROUND	46	Gray/Red

  FUEL INJECTOR TEST PIN NO. IDENTIFICATION
  
  

  Application	Test Pin No.	Wire Color
  Cylinder No. 1	58	Tan
  Cylinder No. 2	59	White
  Cylinder No. 3	39	Brown/Yellow
  Cylinder No. 4	35	Brown/Light Blue
  Cylinder No. 5	15	Tan/Black
  Cylinder No. 6	12	Light Green/Orange
  Cylinder No. 7	13	Tan/Red
  Cylinder No. 8	14	Light Blue

  TEST PIN NO. 37/57 (VPWR) WIRE COLOR IDENTIFICATION
  
  

  Application	Wire Color
  Mark VIII	Red

1. 1) Check For Contaminated Engine Oil
   
   Turn ignition off. Remove PCV valve from valve cover. Inspect PCV system for damage. Inspect valve for blockage and movement of valve plunger. Repair as necessary. Perform KOEO SELF-TEST  and KOER SELF-TEST  . Service ignition continuous memory code (if present) before servicing KOER codes. If vehicle is a no-start, install PCV valve and go to next step. If Code 139, 144, 171, 176 or 177 is present, go to next step. If no codes are set, change engine oil and filter. Install PCV valve, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST  .
2. 2) Check Fuel Pressure
   
   Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Ensure manifold vacuum supply is connected to fuel pressure regulator (if equipped). Run engine at idle and check fuel pressure. If vehicle will not start, cycle ignition on and off several times. Check fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to next step. If pressure is not within specification, repair fuel system as necessary. See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.
3. 3) Check System Ability To Hold Fuel Pressure
   
   Turn ignition on. Check fuel system for leaks. Repair or replace as necessary. If fuel system does not leak and pressure remains at specification for 60 seconds, go to next step (no-starts) or step 6) (all others).
4. 4) Fuel Delivery Test
   
   Release fuel system pressure. With fuel pressure gauge installed, pressurize fuel system as in step 1). Disconnect inertia switch. Crank engine for 5 seconds. If fuel pressure drop is greater than 5 psi after 5 seconds of cranking, EEC-IV system is not causing no-start condition. Check additional no-start tests in the appropriate TESTS W/O CODES article. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge. Connect inertia switch and go to step 8).
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 6). No test procedures have been omitted.
5. 6) Cylinder Balance Test (SFI)
   
   Perform KOER SELF-TEST  . After last code is displayed, wait 5-10 seconds. Enter CYLINDER BALANCE TEST by lightly goosing throttle (not WOT). Test time is about 2-3 minutes. To interpret codes retrieved from test, refer to CYLINDER BALANCE TEST SERVICE CODES  table. If fault codes are present, go to step 8). Code 538 indicates throttle was touched when test was run and test is not completed. Code 538 could also be output if Continuous Memory Code 214 (CID) is present. If Continuous Memory Code 214 is present, see appropriate chart under DIAGNOSTIC TROUBLE CODE REFERENCE CHARTS  for instruction. For Code 136, 172 or 176, go to step 13). For Code 137, 173 or 177, go to step 24). For all other codes, go to step 14).
   CYLINDER BALANCE TEST SERVICE CODES
   
   

   Service Code	Application
   90	Pass
   10	Cylinder No. 1
   20	Cylinder No. 2
   30	Cylinder No. 3
   40	Cylinder No. 4
   50	Cylinder No. 5
   60	Cylinder No. 6
   70	Cylinder No. 7
   80	Cylinder No. 8
   538	Retest

   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 6) to step 8). No test procedures have been omitted.
6. 8) Check Injector & Harness Resistance (SFI)
   
   Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure and record resistance between suspected injector circuit test pin and test pin No. 37 at breakout box. For no-start, measure and record resistance between any injector circuit test pin and test pin No. 37 at breakout box. If resistance is 11-18 ohms, go to step 12). If resistance is not 11-18 ohms, repair open VPWR circuit for no-start or go to next step for all other conditions.
7. 9) Check Continuity Of Fuel Injector Harness
   
   Turn ignition off. Disconnect injector wiring harness connector at suspect injector. Set DVOM to 200-ohm scale. Measure resistance between test pins No. 37 and 57 at breakout box and VPWR terminal at suspect injector wiring harness connector. Also, measure resistance between injector test pin(s) at breakout box and same injector circuit terminal at each injector wiring harness connector. If each reading is less than 5 ohms, go to next step. If any reading is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST  .
8. 10) Check Injector Harness Circuit For Short To Power Or Ground
   
   Turn ignition off. With breakout box installed and PCM disconnected, disconnect suspect fuel injector wiring harness connector. Measure resistance between injector test pin(s) and test pins No. 37, 40, 46, 57 and 60. Also, measure resistance between injector test pin(s) at breakout box and chassis ground. If each resistance is 10,000 ohms or more, replace injector per cylinder balance test service code and repeat QUICK TEST  . 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  .
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 13). No test procedures have been omitted.
9. 13) Check Thermactor Operation
   
   If vehicle is equipped with pulse-air or does not have secondary air injection system, go to next step. A HO2S which is always lean could be caused by thermactor air being diverted upstream from HO2S. With dual HO2S, Code 172 applies to right or rear HO2S and Code 136 or 176 applies to left or front HO2S. Turn ignition off. Disconnect secondary air hose(s) from pump and vent to atmosphere. Perform KOER SELF-TEST  . If Code 172, 136 or 176 is present, reconnect air hose(s) and go next step. If Continuous Memory Code 139, 144, 171, 176 or 177 is present, go to step 90). If Code 311, 312 or 313 is present, go to CIRCUIT TEST KC. If code(s) is not present, repair air injection system as necessary.
10. 14) Check HO2S Integrity
    
    A HO2S which is always lean, slow to switch or does not switch could be caused by:
    • Moisture inside HO2S or connector causing a short to ground.
    • HO2S coated with contaminants.
    • HO2S circuit open.
    • HO2S circuit shorted to ground.

    Turn ignition off. Inspect HO2S wiring harness for damage. Inspect HO2S and connector for signs of fluid entry. Repair or replace as necessary. Start engine, and run it at 2000 RPM for 2 minutes. Turn ignition off. Run KOER SELF-TEST  . If fault codes are present, go to step 16). If no codes are present, go to step 21).

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 14) to step 16). No test procedures have been omitted.
11. 16) Check HO2S (Engines With MAF Sensor)
    
    Purpose of this test is to verify HO2S can generate a voltage signal of greater than 0.5 volt during KOER SELF-TEST. Vacuum or air leaks in non-EEC-IV areas could cause Code 136, 172 or 176. Check following possibilities before continuing:
    • Leaking vacuum actuated motor.
    • Leaking intake gasket.
    • EGR system.
    • PCV system.
    • Unmetered air between MAF sensor and throttle body.
    • Lead-contaminated HO2S.

    Turn ignition off. Disconnect appropriate HO2S from harness. Connect DVOM between HO2S signal circuit terminal and HO2S GND circuit terminal at HO2S wiring harness connector. Run engine at 2000 RPM for 2 minutes. Repeat KOER SELF-TEST  and monitor HO2S voltage. If voltage is 0.5 volt or more at end of self-test, go to next step. If voltage is less than 0.5 volt, replace HO2S and repeat QUICK TEST  .

12. 17) 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, moisture and corrosion. Repair as necessary. Measure resistance between test pin No. 46 at breakout box and HO2S GND circuit terminal at HO2S wiring harness connector. If resistance is less than 5 ohms, go to next step. If 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  .
13. 18) 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. 40, 46 or 49 at breakout box. If any reading is less than 10,000 ohms, repair short to ground. Drive vehicle at 55 MPH for 5 minutes and repeat QUICK TEST  . If reading is 10,000 ohms or more, go to next step.
14. 19) Check HO2S For Short To Ground
    
    Ensure ignition is off and PCM is disconnected. With HO2S disconnected, measure resistance between PWR GND and HO2S circuit terminal at HO2S connector. Also, measure resistance between HO2S circuit terminal and HO2S GND terminal at HO2S wiring harness connector. If resistance is less than 10,000 ohms, replace HO2S. Drive vehicle for 5 miles at 55 MPH and repeat QUICK TEST  . If resistance is 10,000 ohms or more, go to next step.
15. 20) Check Resistance Of HO2S Heating Element
    
    Turn ignition off. Disconnect suspect HO2S. Inspect both ends of connector for damage, moisture and corrosion. Repair as necessary. Measure resistance between IGNITION RUN circuit terminal or VPWR circuit terminal and PWR GND circuit at HO2S connector. Hot to warm engine resistance should be 5-30 ohms. Cold engine temperature resistance is 2-5 ohms. If resistance is within specification, go to next step. If resistance is not as specified, replace HO2S and repeat QUICK TEST  .
16. 21) Check For Power At HO2S Harness Connector
    
    Disconnect HO2S. Turn ignition on. Measure voltage between negative battery terminal and IGNITION RUN circuit terminal at HO2S wiring harness connector. If voltage more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in IGNITION RUN circuit. Reconnect HO2S and repeat QUICK TEST  .
17. 22) Check Continuity Of Power Ground Circuit
    
    Turn ignition off. Measure resistance between PWR GND circuit at HO2S wiring harness connector and negative battery terminal. If resistance is less than 5 ohms, repair open in IGNITION RUN circuit and repeat QUICK TEST  . If resistance is 5 ohms or more, repair open in PWR GND circuit and repeat QUICK TEST  .
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 24). No test procedures have been omitted.
18. 24) Diagnostic Test Code 137, 173 Or 177: Check HO2S SIGNAL For Short To Power
    
    On dual HO2S systems, Code 173 applies to right or rear sensor. Codes 137 and 177 applies to left or front sensor. HO2S continuously rich could be caused by:
    • Moisture inside wiring harness causing short to power.
    • HO2S shorted to power.

    Turn ignition off. Disconnect suspect HO2S. Inspect connector for damage and repair as necessary. Turn ignition on. Measure voltage between HO2S and PWR GND terminals at HO2S wiring harness connector. If voltage is less than 0.5 volt, go to step 26). If voltage is 0.5 volt or more, go to next step.

19. 25) Check For Short To Power
    
    Turn ignition off. Disconnect suspect HO2S. Inspect wiring harness for damage and repair as necessary. Disconnect PCM 60-pin connector. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between VPWR test pin No. 37/57 and HO2S test pin at breakout box. If resistance is 10,000 ohms or more, replace PCM. Remove breakout box, and reconnect all components. Drive vehicle 5 miles at 55 MPH. Repeat QUICK TEST  . If resistance is less than 10,000 ohms, repair short circuit. Remove breakout box, and reconnect all components. Drive vehicle 5 miles at 55 MPH. Repeat QUICK TEST  .
20. 26) Check HO2S For Short To IGNITION RUN Circuit
    
    Turn ignition off. Disconnect HO2S. Measure resistance between IGNITION RUN terminal and HO2S terminal at HO2S connector. If resistance is 10,000 ohms or more, go to next step for Codes 137, 173 and 177 or step 30) for all others. If resistance is less than 10,000 ohms, replace HO2S. Drive vehicle for 5 miles at 55 MPH, and repeat QUICK TEST  .
21. 27) Attempt To Generate Code 136, 172 Or 176
    
    Turn ignition off. Disconnect appropriate HO2S. Connect a jumper wire between negative battery terminal and HO2S terminal at HO2S wiring harness connector. Repeat KOER SELF-TEST  . If Code 136, 172 or 176 is present, remove jumper wire and go to step 30). If Codes 136, 172 or 176 is not present, remove jumper wire. Disconnect PCM connector, and inspect it for damage. If connector is okay, replace PCM. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST  .
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 27) to step 30). No test procedures have been omitted.
22. 30) HO2S Check
    
    Turn ignition off. Disconnect HO2S. Connect DVOM to HO2S terminal and HO2S GND or SIG RTN terminal at HO2S connector. Create a vacuum leak to force HO2S to go lean (disconnect any vacuum hose). Start engine. Raise engine speed to about 2000 RPM. DVOM should indicate less than 0.4 volt within 30 seconds. If voltage is not as specified, replace HO2S. Reconnect vacuum hoses, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST  . If voltage is as specified, go to step 90).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 30) to step 40). No test procedures have been omitted.
23. 40) Code 593: Check HO2S Heater Relay Operation
    
    Code 593 indicates that a primary HO2S heater failure has been detected. Possible causes for this fault are:
    • Damaged HO2S heater relay.
    • Open VPWR circuit.
    • Open in relay control signal circuit.
    • Short to power or ground in relay control signal circuit.
    • Faulty Powertrain Control Module (PCM).

    Turn ignition off. Disconnect both HO2S connectors. Inspect HO2S wiring harness connectors for damage and repair as necessary. Connect DVOM positive lead to VPWR circuit terminal at HO2S wiring harness connector. Connect DVOM negative lead to PWR GND circuit terminal at HO2S wiring harness connector. Enter output state Diagnostic Test Mode (DTM). See OUTPUT STATE DIAGNOSTIC TEST MODE (DTM)  under ADDITIONAL SYSTEM FUNCTIONS. Once output state DTM has been entered, observe DVOM and depress and release throttle several times to cycle outputs. Voltage should cycle between 10.5 volts to less than 0.5 volt. Repeat voltage check on other HO2S connector. If voltage is as specified, fault is intermittent. Reconnect all components and repeat QUICK TEST  . If voltage is not as specified, go to next step (if Code 593 is present) or go to step 46) (all others).

24. 41) Check VPWR Circuit Voltage
    
    Turn ignition off. Disconnect HO2S heater relay. Measure voltage between negative battery terminal and VPWR circuit terminal at HO2S wiring harness connector. If voltage is 10.5 volts or less, repair open circuit. Remove breakout box, reconnect all components and repeat QUICK TEST  . If voltage is more than 10.5 volts, go to next step (if Code 593 is present) or step 46) (all others).
25. 42) Check HO2S Heater Relay Continuity
    
    Turn ignition off. Disconnect HO2S heater relay. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 14 at breakout box and HO2S signal circuit terminal at HO2S wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and repeat QUICK TEST  .
26. 43) Check For Short To Power
    
    Measure resistance between test pin No. 14 and test pins No. 37 and 57. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short to power. Remove breakout box, reconnect all components and repeat QUICK TEST  .
27. 44) Check For Short To Ground
    
    Measure resistance between test pin No. 14 and test pins No. 40, 46 and 60. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short to ground. Remove breakout box, reconnect all components and repeat QUICK TEST  .
28. 45) Check HO2S Heater Relay Coil Resistance
    
    Measure resistance between terminals No. 2 and 3 at HO2S heater relay. See Fig 2 . If resistance is 90-110 ohms, replace PCM. Remove breakout box, reconnect all components and repeat QUICK TEST  . If resistance is not 90-110 ohms, replace relay. Remove breakout box, reconnect all components and repeat QUICK TEST  .
    Fig 2: Identifying HO2S Heater Relay Terminals

    
29. 46) Check For Closed HO2S Heater Relay Contact
    
    Turn ignition off. Disconnect HO2S heater relay connector. Measure resistance between terminal No. 2 (VPWR circuit) and terminal No. 3 (HO2S HTR circuit) at HO2S relay. See Fig 2 . If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, replace relay.
30. 47) Check VPWR Circuit Continuity
    
    Measure resistance between test pin No. 14 at breakout box and VPWR circuit terminal at HO2S relay wiring harness connector (check at both HO2S connectors). If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit.
31. 48) Check Power Ground Continuity
    
    Check resistance between negative battery terminal and PWR GND circuit terminals at both HO2S wiring harness connectors. If resistance is 5 ohms or more, repair open in PWR GND circuit. If resistance is less than 5 ohms, replace HO2S heater relay.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 48) to step 90). No test procedures have been omitted.
32. 90) Check Continuous Monitor Mode
    
    Start engine, and warm it to normal operating temperature. Raise engine speed to 2000 RPM for 2 minutes and then return to idle. Enter KOER wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST)  under QUICK TEST. While observing DVOM or scan tester, shake or bend small sections of wiring harness from HO2S to PCM. Wiggle, shake or bend small sections of wiring harness from HO2S GND to PCM. If no fault is indicated, remain in CONTINUOUS MONITOR MODE and go to next step. If fault is indicated, isolate and repair fault as necessary. Clear codes. Repeat QUICK TEST  .
33. 91) Continuous Monitor Test Drive Check
    
    While still in KOER wiggle test, test drive vehicle for 5 miles at 55 MPH over smooth roads. Drive an additional 5 miles at 55 MPH over rough roads. If possible, drive vehicle through a pool of water to wet HO2S and connector. If fault is indicated, isolate fault and repair as necessary. Clear codes, and remove breakout box. Repeat QUICK TEST  . If no codes are indicated, exit KOER wiggle test and go to next step.
34. 92) Check HO2S Switching
    
    Turn ignition off. Inspect wiring harness for proper routing and insulation. Check for burnt, chaffed or open wires. Repair as necessary. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install breakout box. Connect PCM to breakout box. Connect analog voltmeter to suspect HO2S test pin and HO2S GND at breakout box. Test drive vehicle for 5 miles at 55 MPH while observing voltmeter. HO2S should switch from .3 volt to .9 volt within 3 seconds. If HO2S does not switch as described, replace HO2S. Connect all components, and repeat QUICK TEST  . If HO2S switches as described, fault cannot be identified or duplicated at this time. See INTERMITTENTS in the TESTS W/O CODES article.