Diagnostic Aids

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 1-4 or INJ 1-6, 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.
• Exhaust system leaks or restriction.
• Engine cooling system.

1. 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.
   • Incorrect cam timing.
   • Restricted air cleaner.
   • Faulty PCV system.
   • Excessive internal engine wear.

   Inspect engine for obvious defects in specified systems. Repair or replace as necessary.

   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.
   • EGR system malfunction.
   • Air intake or vacuum system leak.
   • Engine oil level too high.
   • Incorrect cam timing.
   • Restricted air cleaner.
   • Faulty PCV system.
   • 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.

2. Perform KOER Self-Test
   
   Turn ignition off. Connect scan tool to DLC. Disconnect fuel vapor hose from intake manifold and plug fitting at intake manifold. Start engine, and operate at 2000 RPM for 5 minutes. Perform KOER ON-DEMAND SELF-TEST and proceed as follows:
   • If DTC P1127 is present, go to DIAGNOSTIC TEST . See DIAGNOSTIC TROUBLE CODE (DTC) REFERENCE CHARTS in TESTS W/CODES - INTRODUCTION article.
   • If DTC P1130, P1131, P1150 or P1151 is present, go to next step.
   • If DTC P1130, P1132, P1150 or P1152 is present, go to step 9).

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

   • If Continuous Memory DTC P1130, P1150, P0171, P0172, P0174 or P0175 is present, go to step 12).
   • If DTC P1132 or P1152 is no longer present, go to diagnostic test for DTC P0443.
   • On all others without reoccurring DTCs, fault is intermittent. Go to DIAGNOSTIC TEST Z (INTERMITTENT) .

3. HO2S Circuit Test (With Lean DTCs)
   
   Disconnect suspect HO2S. Turn ignition on. Using scan tool, select appropriate HO2S PID (O2S11 or O2S12) from PID/DATA monitor menu. Connect a jumper wire between HO2S SIG and VPWR terminals at suspect HO2S wiring harness connector. If spark occurs, remove jumper wire and go to step 7). If HO2S voltage is greater than 1.3 volts, go to next step. If measured voltage is 1.3 volts or less, go to step 6).
4. Check Circuit Resistance
   
   Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950). Connect PCM to breakout box. Measure resistance between negative battery terminal and SIG RTN terminal at suspect HO2S wiring harness connector. If resistance is less than 5 ohms, go to step 12). If resistance is 5 ohms or more, go to next step.
5. Check For Open Circuit
   
   Turn ignition off. Disconnect PCM from breakout box. Measure resistance between test pin No. 91 (SIG RTN) at breakout box and SIG RTN terminal at suspect HO2S wiring harness connector. If resistance is less than 5 ohms, replace PCM. If resistance is 5 ohms or more, repair open circuit.
6. Check Resistance Of HO2S SIG & Ground Circuits
   
   Turn ignition off. Install breakout box, leaving PCM disconnected. Disconnect suspect HO2S connector. Inspect connectors for loose, damaged or corroded terminals. Repair as necessary. Measure resistance of HO2S SIG circuit between HO2S SIG terminal at suspect HO2S wiring harness connector and appropriate HO2S SIG test pin at breakout box. See HO2S SENSOR SIGNAL TERMINAL IDENTIFICATION  table. Also, measure resistance between SIG RTN terminal at suspect HO2S wiring harness connector and test pin No. 91 at breakout box. If all resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open circuit.
   HO2S SENSOR SIGNAL TERMINAL IDENTIFICATION
   
   

   Application		Test Pin No.
   2.0L Models
   Front HO2S		60
   2.5L Models
   Right Front HO2S		60
   Left Front HO2S		87

7. Check HO2S Circuit For Short To Ground
   
   Measure resistance between test pins No. 23, 24, 51, 77, 91 and 103 and appropriate HO2S SIG test pin. See HO2S SENSOR SIGNAL TERMINAL IDENTIFICATION  table in step 6). If all resistance readings are greater than 10 k/ohms, go to next step. If any resistance reading is 10 k/ohms or less, repair short circuit.
8. Check HO2S For Short To Ground
   
   Reconnect HO2S connector. Measure resistance between test pins No. 91 and 103 and appropriate HO2S SIG test pin. See HO2S SENSOR SIGNAL TERMINAL IDENTIFICATION  table in step 6). If any resistance reading is 10 k/ohms or less, replace HO2S. If all resistance readings are greater than 10 k/ohms, replace PCM.
9. Check HO2S PID
   
   Ensure ignition is off. Disconnect suspect HO2S connector. Turn ignition on. Using scan tool, select appropriate HO2S PID from PID/DATA monitor menu. If PID voltage is greater than .2 volt, go to next step. If PID voltage is .2 volt or less, go to step 11).
10. Check For Short To Power
    
    Turn ignition off. Disconnect scan tool from DLC. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between the following test pins at breakout box:
    • DTC P1130 and P1132 - Measure resistance between test pins No. 60 and test pins No. 71 and 93.
    • DTC P1150 and P1152 - Measure resistance between test pin No. 87 and test pins No. 71 and 94.

    If all resistance readings are greater than 10 k/ohms, replace PCM. If any resistance reading is 10 k/ohms or less, repair short to power.

11. Check For Shorted HO2S
    
    Ensure suspect HO2S is disconnected. Turn ignition on. Using scan tool, select appropriate HO2S PID from PID/DATA monitor menu. If PID voltage is greater than .45 volt, replace HO2S. If PID voltage is .45 volt or less, reconnect all connectors and go to next step.
12. Check Fuel Pressure
    
    Release fuel system pressure. See FUEL SYSTEM in ENGINE CONTROLS - REMOVE/INSTALL/OVERHAUL article. With ignition off, install fuel pressure gauge. Verify vacuum source to fuel pressure regulator (returnable fuel system only). Using scan tool, access OUTPUT TEST MODE. Command fuel pump on. Note fuel pressure. Fuel pressure should be 30-45 psi (2.0-3.2 kg/cm² ). If fuel system pressure is not as specified, go to next step. If fuel system pressure is as specified, go to step 22).
13. Check Pressure Regulator Control (PRC) Solenoid Valve Power Circuit
    
    Possible causes for lack of power due to low fuel pressure are:
    • PRC solenoid malfunction.
    • Damaged vacuum lines.
    • Harness malfunction.
    • PCM malfunction.

    Turn ignition off. Disconnect PRC solenoid harness connector. Turn ignition on. Measure voltage between VPWR terminal on PRC solenoid harness connector and battery ground. If voltage is 10.5 volts or more, go to next step. If voltage is less than 10.5 volts, repair open VPWR circuit and repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.

14. Check PRC Solenoid Valve Harness Circuit Resistance
    
    Turn ignition off. Ensure PRC solenoid harness connector is disconnected. Disconnect PCM 104-pin connector. Inspect for damaged pins and repair if necessary. Connect Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between test pin No. 19 and PRC solenoid terminal at wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
15. Check PRC Solenoid Circuit For Short To Ground Or Power
    
    Leave ignition off and PRC solenoid disconnected. Disconnect scan tool from DLC (if applicable). Measure resistance between test pin No. 19 and test pins No. 24, 71, 77, 91 and 97 at breakout box. If each measurement is 10 k/ohms or more, go to next step. If any measurement is less than 10 k/ohms, repair short circuit and repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
16. Check Vacuum Line
    
    Inspect vacuum line between intake manifold port and PRC solenoid valve. Replace as needed. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article. If vacuum line is okay, go to next step.
17. Check Vacuum Signal
    
    Connect vacuum gauge to PRC solenoid vacuum source. Start and idle engine. If vacuum signal is present, go to next step. If vacuum signal is not present, reconnect all components and go to step 38).
18. Check Vacuum Line
    
    Turn ignition off. Disconnect and inspect vacuum line between fuel pressure regulator and PRC solenoid valve. Replace as needed and run QUICK TEST. See TESTS W/CODES - INTRODUCTION article. If vacuum line is okay, go to next step.
19. Check PRC Solenoid Valve-Stuck Closed
    
    Turn ignition off. Connect Breakout Box (014-00950), leaving PCM connected. Disconnect vacuum line from PRC solenoid valve to fuel pressure regulator at fuel pressure regulator. Install vacuum gauge. Disconnect vacuum line from intake manifold vacuum connection to PRC solenoid valve. Install vacuum pump. Apply 8-10 in. Hg of vacuum. If vacuum is present, go to next step. If no vacuum is not present, replace PRC solenoid valve. Run QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
20. Check PRC Solenoid Valve-Stuck Open
    
    Leave vacuum gauge, vacuum pump and breakout box installed. Apply 8-10 inches of vacuum. Turn ignition on. Momentarily jumper test pins No. 19 and 103. If vacuum reading dropped when test pins were jumpered, go to next step. If vacuum reading did not drop, replace PRC solenoid valve. Run QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
21. Check PCM Control Of PRC Solenoid Valve
    
    Turn ignition off. Leave breakout box connected with PCM connected. Install DVOM between test pins No. 19 and 71. Record voltage readings during following conditions:
    • Key on, engine off.
    • Engine cranking.
    • Engine running.

    If voltage is 10-12 volts during cranking and 0-2 volts during other operating conditions, replace pressure regulator. Remove breakout box and repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article. If voltage is not as specified, replace PCM and repeat QUICK TEST.

22. Check System Ability To Hold Fuel Pressure
    
    With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). If fuel pressure does not remain within 5 psi (.35 kg/cm² ) of maximum pressure after one minute, go to next step. If fuel pressure remains within 5 psi (.35 kg/cm² ) of maximum pressure reading for one minute, proceed as follows:
    • For no-start vehicles, go to step 32).
    • For DTCs P1130, P01150, P0171, P0172, P0174 and P0175, go to step 31).
    • For HO2S DTCs displayed with misfire DTCs, go to step 33).
    • For all other DTCs, go to step 34).
23. 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. If fuel pressure remains within 5 psi (.35 kg/cm² ) of maximum pressure for at least 10 seconds, go to step 25). If fuel pressure drops greater than 5 psi (.35 kg/cm² ), go to next step.
24. Check Pressure Regulator Diaphragm
    
    Turn ignition off. Ensure fuel pressure gauge is installed. Start and run engine for 10 seconds. Turn ignition off. Wait 10 seconds. Start and run engine for 10 seconds. Turn ignition off. Remove vacuum hose from fuel pressure regulator. If fuel is present in vacuum hose, replace pressure regulator and repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article. If no fuel is present in vacuum hose, go to next step.
25. Check Fuel Pressure-Engine Running
    
    Turn ignition off. With fuel pressure gauge installed, disconnect vacuum hose at fuel pressure regulator. Plug vacuum hose. Test drive vehicle. While monitoring fuel pressure gauge, accelerate at 3/4 to full throttle. Repeat several times. If fuel pressure remains steady within 3 psi (.21 kg/cm² ) while accelerating, connect vacuum hose to regulator and go to next step. If fuel pressure does not remain steady, go to step 29).
26. Check Fuel Pressure Regulator Response To Vacuum
    
    Turn ignition off. Install vacuum gauge to intake manifold. Start and run engine. While monitoring fuel pressure gauge and vacuum gauge, accelerate and decelerate engine speed. Fuel pressure should increase as vacuum decreases and fuel pressure should decrease as vacuum increases. If fuel pressure is as specified, fuel pressure regulator is operating correctly. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article. If fuel pressure is not as specified, go to next step.
27. Check Vacuum Supply
    
    Turn ignition off. Disconnect vacuum hose at fuel pressure regulator and plug vacuum hose. Install vacuum pump to fuel pressure regulator. Start and run engine at idle. Apply vacuum to pressure regulator. Monitor fuel pressure while varying vacuum. If fuel pressure changes, inspect and repair vacuum system. If fuel pressure does not change, replace fuel pressure regulator and repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
28. Check Fuel Injector Flow & Leakage
    
    Turn ignition off. Use appropriate fuel injector tester 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, replace fuel pump. Recheck fuel pressure.
29. Check Voltage At Fuel Pump Connector
    
    Ensure vehicle has fuel in tank. Disconnect fuel pump connector. Turn ignition on. Connect DVOM between fuel pump power circuit terminal and ground terminal at fuel pump wiring harness connector. See appropriate wiring diagram in ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article. Using scan tool, access OUTPUT TEST MODE. Command fuel pump on and observe DVOM voltage reading. If voltage is greater than 10.5 volts, exit output test mode. Reconnect fuel pump connector and go to next step. If voltage is 10.5 volts or less, inspect and repair fuel pump power and ground circuits. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
30. Check Supply Fuel Line For Restrictions
    
    Turn ignition off. Inspect fuel system for leaks, damage or kinked hoses. Inspect fuel system related wiring harness connectors for loose, damaged or corroded terminals. Repair as necessary. Recheck fuel pressure. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article. If fuel lines are okay, replace fuel pump and recheck fuel pressure.
31. Check Ability To Hold Fuel Pressure With Ignition On
    
    With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). Note fuel pressure. If fuel pressure remains within 5 psi (.35 kg/cm² ) of maximum pressure for at least 10 seconds, go to step 33). If fuel pressure drops greater than 5 psi (.35 kg/cm² ), go to step 35).
32. Check Ability Of Injectors To Deliver Fuel
    
    With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). Note fuel pressure. Crank engine for 5 seconds. If fuel pressure remains within 5 psi (.35 kg/cm² ) of maximum pressure and go to next step. If fuel pressure drops greater than 5 psi (.35 kg/cm² ), electronic engine control system is not cause of no-start. Reconnect all components. See TESTS W/CODES - INTRODUCTION article for further diagnosis of no-start.
33. Check Fuel Injector & Circuit Resistance
    
    Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure and record resistance between suspect fuel injector circuit test pin and test pin No. 71/97 at breakout box. See FUEL INJECTOR CIRCUIT IDENTIFICATION  table. Resistance should be 12-16 ohms. If resistance is not as specified, go to next step. If measured resistance is as specified, go to step 36).
    NOTE: If misfire DTCs are present with fuel control DTCs, use misfire DTCs to determine which fuel injector circuits require testing.
    FUEL INJECTOR CIRCUIT IDENTIFICATION
    
    

    Injector No.	Test Pin No.
    1	75
    2	101
    3	74
    4	100
    5	73
    6	99

34. Check Resistance Of Fuel Injector Circuit
    
    Turn ignition off. Disconnect suspect fuel injector connector. Measure resistance between test pin No. 71/97 at breakout box and VPWR terminal at suspect fuel injector wiring harness connector. Also, measure resistance between fuel injector signal test pin(s) at breakout box and same fuel injector circuit terminal at suspect fuel injector wiring harness connector. If all resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open circuit.
35. Check Fuel Injector Circuit For Short To Power Or Ground
    
    Measure resistance between fuel injector test pin(s) 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 all resistance readings are greater than 10 k/ohms, go to next step. If any resistance reading is less than 10 k/ohms, repair short circuit.
36. Check Fuel Injector Drive Signal
    
    With ignition off, connect PCM to breakout box. Connect non-powered, 12-volt test light between suspect fuel injector test pin and test pin No. 71. Crank or start engine. If test light glows dimly, system is functioning properly. Reconnect all components and go to next step. If test light does not glow dimly (no light/bright light), replace PCM.
37. Check Fuel Injector Flow & Leakage
    
    Turn ignition off. Remove breakout box. Reconnect PCM and fuel injector connector(s). Use appropriate fuel injector tester 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, P0174, P1130, P1131, P1150 and P1151, go to next step.
    • For DTCs P1132 and P1152, go to step 41).
    • For DTCs P0172 and P0175, fault is intermittent. Go to DIAGNOSTIC TEST Z (INTERMITTENT) .
38. Check Air Induction System
    
    Check air induction system for leaks. Check PCV system for leaks. Check vacuum hoses for damage and tight connections. Check intake manifold gaskets. If any faults are found, repair as necessary. If no faults are found, proceed as follows:
    • For Continuous Memory DTCs P0171, P0174, P1130 or P1150, fault is intermittent. Go to DIAGNOSTIC TEST Z  (INTERMITTENT).
    • For DTCs P1131 and P1130, or P1151 and P1150, go to next step.
39. Check Cylinder Compression
    
    Using compression gauge, check cylinder compression. If cylinder compression is not okay, repair engine as necessary. If compression is okay, proceed as follows:
    • For DTCs P1130, P1131, P1150 and P1151, go to next step.
    • For DTCs P1132 and P1152, go to step 41). If misfire DTCs are displayed with fuel control DTCs, go to appropriate DTC test.
40. Check HO2S Integrity
    
    Any vacuum or air leaks can cause DTCs P1130, P1131, P1150, and P1151. Possible causes are:
    • Leaking vacuum actuators.
    • HO2S coated with contaminates.
    • Faulty EGR valve.
    • Faulty PCV system
    • Unmetered air leaks between throttle body and MAF sensor.
    • Engine sealing problems (intake and IAC valve)

    Turn ignition off. Inspect HO2S wiring harness for chafing, burned wires or other damage. Repair as necessary. Disconnect suspect HO2S connector. Connect DVOM between SIG RTN terminal and HO2S SIG terminal at suspect HO2S. Start engine and operate at 2000 RPM for 3 minutes. Using scan tool, perform KOER ON-DEMAND SELF-TEST while monitoring HO2S voltage. If HO2S voltage is greater than .5 volt during or at end of test, go to step 43). If voltage is .5 volt or less, replace HO2S sensor. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.

41. Perform KOER Self-Test
    
    Start engine, and warm it to normal operating temperature. Turn ignition off. Disconnect suspect HO2S. Connect a jumper wire between HO2S SIG terminal at suspect HO2S wiring harness connector and negative battery terminal. Using scan tool, 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 and repair as necessary. If connector is okay, replace PCM.
42. HO2S Check
    
    Leave suspect HO2S disconnected. Connect DVOM between HO2S SIG terminal and SIG RTN terminal at suspect HO2S wiring harness connector. Disconnect any vacuum hose from vacuum tree. Start engine and operate at 2000 RPM. If DVOM reads less than .4 volt within 30 seconds, go to next step. If DVOM does not read .4 volt within 30 seconds, replace HO2S. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.
43. Monitor HO2S PID
    
    Start engine and allow to idle. Ensure engine is at normal operating temperature. Using scan tool, select HO2S PID from PID/DATA monitor menu. Observe PID value while wiggling and bending wiring harness between HO2S and PCM. If PID voltage stays high (greater than .45 volt) or stays low (less than .45 volt), isolate fault and repair as necessary. If PID voltage switches, go to next step.
44. Monitor HO2S PID During Test Drive
    
    Using an assistant, test drive vehicle under various conditions while observing HO2S PID. 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. Repeat QUICK TEST. See TESTS W/CODES - INTRODUCTION article.