Diagnostic Aids

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

• Ignition system.
• Fuel pressure.
• Fuel injectors.
• Engine vacuum system.
• Evaporative system.
• Canister purge solenoid.
• Internal engine wear.

1. 1) Check Possible Cause Of Misfire
   
   If vehicle runs out of fuel, a trouble code may be stored in PCM memory. Check if vehicle has run out of fuel recently. If vehicle has run out of fuel recently, clear PCM memory and repeat QUICK TEST . If no DTCs are present, system is functioning properly. If vehicle has not recently run out of fuel, go to next step.
2. 2) Check Crankshaft Pulley
   
   On models equipped with crankshaft pulley-mounted pulse ring, check crank pulley and pulse ring for damage or looseness. On models not equipped with crankshaft pulley-mounted pulse ring, remove front cover if necessary. Check crank pulley and pulse ring for damage or looseness. On all models, repair as necessary. If no faults are found, go to next step.
3. 3) Check For Continuous DTCs
   
   Check for other non-misfire Continuous Memory DTCs which could cause the misfire DTC. If DTC P0136, P0156, P0171, P0172, P0175, P1130 or P1150 is present, go to step  5). If specified DTCs are not present, go to next step.
4. 4) Check For Any Other Continuous DTCs
   
   Check for other non-misfire Continuous Memory DTCs which could cause the misfire DTC. If any other Continuous Memory DTCs are present, service next Continuous Memory DTC as necessary. Disregard misfire DTCs at this time. If no other Continuous Memory DTCs are present, go to next step.
5. 5) Check For KOEO DTCs
   
   Check for any KOEO DTCs which could cause the misfire DTC. If any KOEO DTCs are present, service DTCs as necessary. Disregard misfire DTCs at this time. If any other DTCs are present, perform appropriate system test. If no KOEO DTCs are present, check spark plugs and spark plug wires. If spark plugs and spark plug wires are okay, go to next step.
6. 6) Check For KOER DTCs
   
   If any KOER DTCs except P1131, P1132, P1137, P1138, P1151 or P1157 are present, service DTCs as necessary. Disregard misfire DTCs at this time. If KOER DTC P1131, P1132, P1137, P1138, P1151 or P1157 is present, go to step  8). If no KOER DTCs are present, go to next step (models equipped with Differential Pressure Feedback (DPF) EGR system) or go to step  8) (models not equipped with DPF EGR system).
7. 7) Check/Compare PID Values
   
   Turn ignition and all accessories off. Ensure engine is warmed to normal operating temperature. Turn ignition on. Using scan tool, select and record DPFEGR PID voltage. Start engine and allow to idle. Record DPFEGR PID voltage. If both DPFEGR PID voltage values are within .15 volt of each other, go to next step. If DPFEGR PID voltages are not within .15 volt of each other, go to  TEST HE, step 100).
8. 8) Check Injector Driver PIDs
   
   Turn ignition on. Using scan tool, select and record appropriate injector PID for suspect injector. If injector PID value indicates YES, go to next step. If injector PID value indicates NO, go to step  10).
9. 9) Check Fuel Injector & Circuit Resistance
   
   Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure and record resistance between suspected fuel injector pin and pin No. 71 (VPWR) at PCM connector. See MISFIRE TROUBLE CODES  table for PCM injector pin identification. If resistance is 11-18 ohms, replace PCM. If resistance is not 11-18 ohms, go to  TEST H, step 57).
10. 10) Check Fuel Pressure
    
    Turn ignition off. Release fuel pressure. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. Note fuel pressure. If fuel pressure is 80-120 psi (552-827 kPa) on Natural Gas vehicles or 30-60 psi (207-413 kPa) on all other models, go to next step. If fuel pressure is not as specified, check and repair fuel system as necessary.
11. 11) Check System Ability To Hold Fuel Pressure
    
    Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. Check for fuel leaking from around fuel injectors, fuel pressure regulator and fuel hoses. Repair as necessary. Turn ignition off and note fuel pressure gauge reading. If fuel pressure remains within 5 psi (35 kPa) of specification for one minute, go to next step. If fuel pressure does not remain within 5 psi (35 kPa) of specification for one minute, check fuel system and repair as necessary.
12. 12) Check Fuel Injector Flow & Leakage
    
    Turn ignition off. Use Rotunda injector tester from Fuel Tester Kit (113-00114) to flow test fuel injectors. Follow injector tester instructions. If flow rate for each fuel injector is okay, go to next step. If flow rate for any fuel injector is not okay, clean or replace defective fuel injector. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS.
    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.
13. 20) Check Vacuum System
    
    Inspect all vacuum hoses for kinks or damage. Ensure all vacuum connections are clean and tight. Repair as necessary. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS. If vacuum system is okay, go to next step.
NOTE: The misfire monitor can be affected by the evaporative emission system.
14. 21) Check Evaporative Emission System
    Inspect carbon (charcoal) canister for fuel saturation. Replace carbon canister if canister contains liquid fuel. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS. If carbon canister is okay, go to next step.
15. 22) Pressure Test Evaporative System
    
    Using Rotunda Evaporative Emission System Tester (134-00056), pressure test evaporative system starting at EVAP service port (if equipped) then at fuel filler cap. Follow evaporative emission system tester instructions. If evaporative emission system holds pressure, go to next step. If system does not hold pressure, isolate fault and repair as necessary. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS.
16. 23) Check Vacuum In Evaporative System
    
    Inspect vacuum hoses between engine and carbon canister for restrictions or damage. Ensure all vacuum connections are clean and tight. Check for fuel tank vent system blockage. Repair as necessary. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS. If no faults are found, go to step  26).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 23) to step 25). No test procedures have been omitted.
17. 25) Check Engine Condition
    
    Inspect engine for obvious faults. Ensure compression is okay. Check PCV system for restrictions or leaks. Repair as necessary. If no faults can be found, misfire trouble code is intermittent. Go to  TEST Z, step 50).
18. 26) Check EVAP Canister Purge Control Valve (CPCV) Housing
    
    Turn ignition off. Ensure vehicle is at room temperature. Connect vacuum pump to fuel vapor port at EVAP CPCV and apply 16 in. Hg. If vacuum holds, go to next step. If vacuum releases, replace EVAP CPCV.
19. 27) Check For Filter Contamination
    
    Disconnect hose from vacuum input port of EVAP CPCV. Connect vacuum pump to EVAP CPCV vacuum input port and apply 10-15 in. Hg. If little or no vacuum is lost, service EVAP CPCV filter. If filter is okay, replace EVAP CPCV. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS. If vacuum is not as specified, reconnect all components and go to step  25).
    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.
20. 30) Check For Additional Misfire DTCs
    
    DTC P0300 indicates multiple cylinders are misfiring or PCM cannot identify which cylinder is misfiring. If any other misfire DTCs are present, go to step  1). If no other misfire DTCs are present, go to next step.
21. 31) Check For Continuous DTCs
    
    If any other Continuous Memory DTCs are present, service DTCs as necessary. If no other Continuous Memory DTCs are present, go to next step.
22. 32) Check/Compare PID Values
    
    Turn ignition and all accessories off. Ensure engine is warmed to normal operating temperature. Turn ignition on. Using scan tool, select DPFEGR PID from PID/DATA monitor menu. Record PID voltage. Start engine and allow to idle. Again, record DPFEGR PID voltage. If both PID voltage values are within .15 volt of each other, go to step  40) (models with Hall Effect type camshaft position sensor) or go to step  41) (models with variable reluctance type camshaft position sensor). If DPFEGR PID voltage is not as specified, go to  TEST HE, step 100).
    NOTE: Hall Effect type camshaft position sensor has a 3-pin connector. Variable reluctance type camshaft position sensor has a 2-pin connector.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 32) to step 40). No test procedures have been omitted.
23. 40) DTC P1309
    
    This fault indicates misfire detection monitor malfunction. Turn ignition and all accessories off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Connect DVOM between PCM connector pins No. 85 (CMP) and 103 (PWR GND). Using starter, bump engine in short bursts for at least 10 revolutions. DO NOT allow engine to start. If voltage switches from less than 2 volts to more than 8 volts, check CMP sensor for correct installation. If sensor is correctly installed, replace PCM. If voltage does not switch from less than 2 volts to more than 8 volts, replace CMP sensor. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS.
24. 41) Check CMP Sensor Output
    
    Turn ignition and all accessories off. Ensure PCM is connected. Connect DVOM between PCM connector pins No. 85 and 103. Start engine and vary engine speed. If A/C voltage varies more than .1 volt, check CMP sensor for correct installation. If sensor is correctly installed, replace PCM. If voltage does not vary more than .1 volt, replace CMP sensor. Perform MISFIRE MONITOR REPAIR VERIFICATION DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS.