Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedure. This test is intended to diagnose the following:

• HO2S heater.
• HO2S and sensor connection.
• Vacuum systems.
• Fuel injector and/or fuel injector circuitry.
• Powertrain Control Module (PCM).
• Harness circuits: HO2S, HO2SH, INJ 1-6 and VPWR.

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.

Fig 1: Identifying FPRC Solenoid Harness Connector Terminals

Fig 2: Identifying HO2S Circuits

Fig 3: Identifying Fuel Injector Circuits & Connector Terminals

1. 1) DTC P0130 & P0150: HO2S Circuit Malfunction  DTCs P0130 and P0150 indicate an irrational value in upstream (H)O2S circuit. Possible causes for fault are as follows:
   • Damaged upstream (H)O2S.
   • Fault in intake air system.
   • Fuel system malfunction.
   • Ignition system malfunction

   Turn ignition off. Connect NGS scan tool to OBD-II DLC. Start engine and run until engine is at normal operating temperature. Access HO2S PIDs. Run engine at different speeds while observing HO2S PID. If HO2S PID is not constantly varying between 0.4-1.0 volt, go to step 30). If HO2S PID is 0.4-1.0 volt and constantly varying, HO2S is okay at this time. Go to CIRCUIT TEST Z  or TESTS W/O CODES - 2.5L article for intermittent diagnostic procedure.

   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 1) to step 10). No test procedures have been omitted.
2. 10) DTC P0134, P0154, P1170 & P1173  DTC P0134 and P0154 indicate that upstream HO2S signal does not exceed 0.5 volt for more than 2 minutes with engine running at more than 1500 RPM.

   DTC P0136, P0140 & P0146 indicate downstream HO2S signal does not exceed 0.5 volt for more than 2 minutes with engine running at 1500 RPM.

   DTC P1169 indicates pre-catalyst HO2S signal remain unchanged for 20 seconds after closed loop operation began.

   DTC P1170 and P1173 indicate upstream HO2S signals remain unchanged for 20 seconds after closed loop operation began.

   NOTE: DTC P0154 and P1173 indicate fault in sensor located on left exhaust pipe. See Fig 4.

   Check for following conditions:

   • Faulty or damaged HO2S.
   • Poor harness connections.
   • Intake air system or fuel system malfunction.
   • Faulty PCM.

   If harness connections are okay and no apparent damage to HO2S exists, go to next step. If connection is faulty or HO2S damage is apparent, replace or repair as necessary.

3. 11) Check HO2S Output Voltage  Warm engine to normal operating temperature. Turn ignition off. Connect NGS scan tool to OBD-II DLC. Access HO2S PIDs. Start engine and run at 2000 RPM while observing HO2S PID. If HO2S reaches 0.5 volt or greater, go to step 14). If HO2S never reaches 0.5 volt or greater, go to next step.
4. 12) Check HO2S Circuit Continuity  Turn ignition off. Disconnect suspect HO2S connector. Disconnect PCM connector. Inspect connector for damage pins and repair if necessary. Install breakout box (leave PCM disconnected). Measure resistance between suspect HO2S harness connector and appropriate HO2S test pin at breakout box. See Fig 2. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open HO2S circuit. Repeat QUICK TEST.
5. 13) Check HO2S Signal Short To Ground  Turn ignition off. Disconnect suspect HO2S sensor(s). Install breakout box (leave PCM disconnected). Measure resistance between ground and breakout box test corresponding to suspect HO2S. If resistance is less than 10,000 ohms repair short to ground in HO2S circuit. Repeat QUICK TEST. If resistance is greater than 10,000 ohms, perform step 30). If all systems are okay, go to step 15).
6. 14) Check For Short To Power  Turn ignition off. Disconnect suspect HO2S sensor(s). Install breakout box (leave PCM disconnected). Turn ignition on. Measure voltage between ground and breakout box test pin corresponding to suspect HO2S. If one volt or more is present, repair short to power in HO2S circuit. If less than one volt is present, perform step 30). If all systems are okay, go to step 15).
7. 15) Erase DTCs  Erase DTCs from memory. See CLEARING CODES. Run engine at 1500-2000 RPM for at least 3 minutes. Repeat QUICK TEST. If DTC does not return, go to CIRCUIT TEST Z  or TESTS W/O CODES - 2.5L article for intermittent diagnostic procedure. If same DTC returns, replace HO2S in question. Perform QUICK TEST again, if same DTC returns, replace PCM.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 15) to step 20). No test procedures have been omitted.
   NOTE: DTC P0155 indicates fault in sensor located in left exhaust pipe. See Fig 4.
   Fig 4: Identifying HO2S locations

   
8. 20) DTC P0135 & P0155: Heater Circuit Malfunction  DTC P0135 and P0155 indicate a malfunction in upstream HO2S heater circuit. Possible causes for malfunction are as follows:
   • Faulty or damaged HO2S.
   • Poor harness connection.
   • Open or short in heater circuit.
   • Open heater GND circuit.
   • Faulty PCM.

   Examine HO2S harness connectors for damage or corrosion etc. Repair connectors as necessary. If HO2S harness connectors are okay, go to next step.

9. 21) Check HO2S Heater PID  Turn ignition off. Connect NGS scan tool to OBD-II DLC. Access appropriate HO2SH PID. Start engine and observe HO2SH PID. If HO2SH PID indicates ON for approximately 4 minutes after engine is started, go to step 23). If HO2SH PID indicates ON for longer than 4 minutes after engine is started, go to next step. If HO2SH PID does not indicate ON at all, go to step 23).
10. 22) Check HO2SH Circuit For Short To Ground  Turn ignition off. Disconnect suspect HO2S sensor(s). Install breakout box (PCM disconnected). Measure resistance between HO2SH11 or HO2SH21 and ground. If resistance is less than 10,000 ohms, repair short to ground in HO2SH circuit. Repeat QUICK TEST. If resistance is greater than 10,000 ohms, go to next step.
11. 23) Check VPWR Circuit Continuity  Turn ignition off. Disconnect suspect HO2S sensor(s). Turn ignition on. Measure voltage at VPWR terminal at HO2S harness connector and ground. If voltage is greater than 10.5 volts, go to next step. If voltage is less than 10.5 volts, repair open VPWR circuit. Repeat QUICK TEST.
12. 24) Check HO2S Heater Circuit Continuity  Turn ignition off. Disconnect suspect HO2S sensor(s). Install breakout box (PCM disconnected). Measure resistance between heater circuit terminal at harness connector and breakout box test pin HO2SH11 or HO2SH21. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open HO2SH circuit. Restore electrical connections and repeat QUICK TEST.
13. 25) Check HO2S Heater  Turn ignition off. Disconnect suspect HO2S. Measure resistance between ground and heater terminal at component harness connector. If resistance is approximately 6 ohms, replace PCM. Restore electrical connections and repeat QUICK TEST. If resistance is not approximately 6 ohms, replace HO2S. Restore electrical connections and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 30). No test procedures have been omitted.
14. 30) DTC P0170 & P0173: Fuel Trim Malfunction  DTC P0170 indicates cylinder bank No. 1 air/fuel ratio too lean or rich. DTC P0173 indicates cylinder bank No. 2 air/fuel ratio too lean or rich. Possible causes for malfunction are as follows:
    • Excessive fuel pressure.
    • Leaking fuel injector.
    • Leaking fuel pressure regulator.
    • Low fuel pressure.
    • Restricted fuel injectors.
    • Faulty HO2S or circuit.
    • Induction system air leaks.
    • Restricted air filter.
    • Faulty PCV system.
    • Engine mechanical problem.
    • Ignition system malfunction.

    If any of the above areas are faulty, repair as necessary. If all of the above areas are okay, go to next step.

15. 31) Fuel Pressure Check  Connect fuel pressure gauge to fuel rail or fuel filter. Locate diagnostic connector next to battery. Jump FP terminal in diagnostic connector to ground. Turn ignition on and observe fuel pressure. 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, go to CIRCUIT TEST HC .
16. 32) Check Fuel Pressure Leak-Down  With fuel pressure gauge installed, turn ignition switch on and off several times. Turn ignition off and observe fuel pressure gauge. If fuel pressure drops less than 5 psi in one minute, go to next step. If fuel pressure drops 5 psi or more in one minute, check for external leaks. If no external leakage is found, check fuel injectors, fuel pressure regulator and fuel pump check valve for internal leakage. See CIRCUIT TEST HC .
17. 33) Check Vacuum To Pressure Regulator  Turn ignition off. Disconnect vacuum hose from fuel pressure regulator. Start engine and check for vacuum at disconnected hose. If vacuum is present, go to next step. If vacuum is not present, check for damaged vacuum hose, etc. and repair as necessary.
18. 34) Check Injector Circuit Resistance  Turn ignition off. Disconnect PCM and inspect connector for corroded or pushed out pins etc. Repair as necessary. Install breakout box (leave PCM disconnected). Measure resistance between breakout box test pin VPWR and fuel injector test pins. See FUEL INJECTOR TEST PINS table. If resistance is 12-16 ohms, fuel injector circuit is okay, go to step 37). If resistance is not 12-16 ohms, go to step 35).
    FUEL INJECTOR TEST PINS
    
    

    Cyl. No.	Pin No.
    1	82
    2	85
    3	88
    4	91
    5	94
    6	97

19. 35) Check Injector Harness  Turn ignition off. Breakout box installed (PCM disconnected). Disconnect injector harness connectors. Measure resistance between breakout box test pin VPWR and VPWR terminal at each injector harness connector. Measure resistance between injector signal terminal at injector harness and appropriate breakout box test pin. See FUEL INJECTOR TEST PINS table. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open harness circuit as necessary. Restore electrical connections and repeat QUICK TEST.
20. 36) Check Injector Harness For Short To Power Or Ground  Turn ignition off. Breakout box installed (PCM disconnected). Disconnect injector harness connectors. Measure resistance between breakout box test pins VPWR, GND and SIG RTN. Measure resistance between injector test pin at breakout box and ground. See FUEL INJECTOR TEST PINS table. If all resistance measurements are 10,000 ohms or greater, go to next step. If any resistance measurement is less than 10,000 ohms, repair shorted harness circuit as necessary. Restore electrical connections and repeat QUICK TEST.
21. 37) Check Injector Driver  Turn ignition off. Breakout box installed (PCM connected). Connect a standard non-powered test light between breakout box test pin VPWR and each injector test pin. See FUEL INJECTOR TEST PINS table. Crank engine. If test light dimly glows while cranking, remove breakout box and go to next step. If test light does not glow or glows brightly, replace PCM. Restore electrical connections and repeat QUICK TEST.
22. 38) Check Injector Flow  Using Rotunda Fuel Injector Tester Cleaner (164-R3750), test suspect injector flow. Replace any injector that are not within leakage and flow specification. If all injectors are within leakage and flow specification, fault is intermittent. See CIRCUIT TEST Z . Also check PIDs SHRTFT1, SHRTFT2, LONGFT1, LONGFT2.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 38) to step 40). No test procedures have been omitted.
23. 40) DTC P1250: Check VPWR To FPRC Solenoid  DTC P1250 indicates a fault in Fuel Pressure Regulator Control (FPRC) solenoid circuit. Possible causes for malfunction are as follows:
    • Damaged FPRC solenoid.
    • Open or shorted circuit.
    • Faulty PCM.

    Turn ignition off. Disconnect FPRC solenoid harness connector. Turn ignition on. Measure voltage on VPWR terminal at FPRC harness connector. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open VPWR circuit. Restore electrical connections and repeat QUICK TEST.

24. 41) Check FPRC Solenoid Operation  Turn ignition off. Install breakout box (leave PCM disconnected). Apply 12 volts to breakout box test pin VPWR and ground test pin FPRC. If FPRC solenoid clicks, go to next step. If FPRC solenoid does not click, go to step 43).
25. 42) Check FPRC Solenoid Valve  Turn ignition off. Install breakout box (leave PCM disconnected). Using a vacuum pump, apply vacuum to supply port of FPRC solenoid. Apply 12 volts to breakout box test pin VPWR and ground test pin FPRC. If solenoid holds vacuum when power and ground are applied, replace PCM. Restore electrical connections and repeat QUICK TEST. If solenoid cannot hold vacuum when power is applied or release vacuum when power is removed from solenoid, replace solenoid. Restore electrical connections and repeat QUICK TEST.
26. 43) Check FPRC Circuit For Open Or Short To Ground  Turn ignition off. Breakout box installed (PCM disconnected). Disconnect FPRC solenoid harness connector. Measure resistance between breakout box test pin FPRC and FPRC circuit at harness connector. Measure resistance between breakout box test pin FPRC and ground. If resistance is 5 ohms or less between test pin and harness connector and greater than 10,000 ohms between FPRC test pin and ground, go to next step. If resistance is not as specified, repair circuit as necessary. Restore electrical connections and repeat QUICK TEST.
27. 44) Check FPRC Circuit For Short To Power  Turn ignition off. Breakout box installed (PCM disconnected). Turn ignition on. Measure voltage between breakout box test pin FPRC and ground. If voltage is greater than one volt, repair short to power in FPRC circuit. If voltage is less than one volt, replace PCM. Restore electrical connections and repeat QUICK TEST.