Diagnostic Aids
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Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:
- Throttle linkage.
- Wiring harness circuits (IAC and VPWR).
- Faulty Idle Air Control (IAC) valve.
- Faulty throttle body.
- Faulty Powertrain Control Module (PCM).
- 1) Check For DTCs
Retrieve and record all Continuous Memory DTCs. Perform KOER ON-DEMAND SELF-TEST . If unable to complete KOER SELF-TEST, go to next step. If KOER SELF-TEST is complete and DTC P0505, P1504 or P1507 is present, go to next step. If DTC P0505, P1504 or P1507 is not present, IAC system is okay and testing is complete. If symptom exists, go to TROUBLE SHOOTING - NO CODES - EEC-V article. - 2) DTC P0505, P1504 & P1507
DTCs P0505 and P1504 indicate IAC system malfunction has been detected. DTC P1507 indicates that IAC system under speed fault has been detected. Possible causes are:- IAC circuit open or shorted to PWR.
- VPWR circuit open.
- Contaminated IAC valve assembly.
- Damaged throttle body.
- Faulty IAC valve.
- Faulty PCM.
Turn ignition off. Disconnect IAC valve connector. Turn ignition on. Measure voltage between VPWR terminal at IAC valve wiring harness connector and ground. See Fig 1. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in VPWR circuit.
- 3) Check IAC Valve Resistance
Turn ignition off. Connect DVOM positive lead to VPWR terminal at IAC valve. Connect DVOM negative lead to IAC terminal at IAC valve. If resistance is 6-13 ohms, go to next step. If resistance is not 6-13 ohms, replace IAC valve assembly. - 4) Check IAC Valve Internal Short To Case
Turn ignition off. Measure resistance between each IAC valve terminal and IAC housing. If both resistance readings are more than 10,000 ohms, go to next step. If any resistance reading is 10,000 ohms or less, replace IAC valve assembly. - 5) Check For Plugged Air Inlet System
Turn ignition off. Remove air filter. Inspect air filter, MAF sensor and air inlet system for excessive dirt or contamination. Repair as necessary. If air inlet system is okay, go to next step. - 6) Check For Vacuum Leaks
Start engine and allow to idle. Inspect air inlet system any of the following possible faults:- Cracked or punctured air inlet tube.
- Loose inlet air tube or air cleaner housing.
- Loose or damaged throttle body.
- Contaminated or damaged IAC valve assembly.
- Faulty EGR valve or gasket.
- Faulty PCV valve or hose.
Check entire intake air system for vacuum leaks. Repair as necessary. If no vacuum leaks are found, go to next step.
- 7) Check IAC Circuit Continuity
Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM connector pin No. 83 (IAC) and IAC terminal at IAC valve wiring harness connector. If resistance is 5 ohms or more, repair open in IAC circuit. If resistance is less than 5 ohms, go to next step. - 8) Check IAC Circuit For Short To Power
Turn ignition on. Measure voltage between PCM connector pin No. 83 (IAC) and chassis ground. If voltage is one volt or more, repair short to power in IAC circuit. If voltage is less than one volt, go to next step. - 9) Check IAC Circuit For Short To Ground
Turn ignition off. Disconnect scan tool from DLC. Measure resistance between PCM connector pin No. 83 (IAC) and pins No. 51 and 103 (PWR GND). If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short to ground in IAC circuit. - 10) Check IAC Signal From PCM
Reconnect PCM connector. Reconnect IAC valve connector. Start engine and allow it to idle. Using scan tool, select IAC and RPM PIDs from PID/DATA monitor menu. Ensure engine is at normal operating temperature. With all accessories off and throttle closed, IAC duty cycle should be about 22-45 percent. Observe PID value and slowly increase engine speed to 3000 RPM, then return to closed throttle position (if closed throttle RPM is significantly higher than normal, ignore this part of the procedure). IAC duty cycle should increase as engine speed increases. If IAC PID values are not as specified, replace IAC valve (DTC P1507) or replace PCM (all others). If IAC PID values are as specified, proceed as follows:- If Continuous Memory DTC P1504 or P1507 is present, go to step 30).
- If Continuous Memory DTC P1504 or P1507 is not present, check throttle body for damage. Repair as necessary. If throttle body is okay, replace IAC valve.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 20). No test procedures have been omitted. - 20) DTC P1506
This DTC indicates IAC system has reached over speed malfunction. Possible causes are:- IAC circuit short to ground.
- IAC assembly stuck open.
- Air intake leaks or restrictions.
- Damaged throttle body.
- Contaminated or damaged IAC valve assembly.
- Faulty Powertrain Control Module (PCM).
Start engine and allow to idle. Inspect air inlet system any of the following possible faults:
- Cracked or punctured air inlet tube.
- Loose inlet air tube or air cleaner housing.
- Loose or damaged throttle body.
- Contaminated or damaged IAC valve assembly.
- Faulty EGR valve or gasket.
- Faulty PCV valve or hose.
Check entire intake air system for vacuum leaks. Repair as necessary. If no vacuum leaks are found, go to next step.
- 21) Check EVAP System For Stuck Valve
Turn ignition off. Disconnect hoses from EVAP canister purge valve. Connect a vacuum pump to carbon canister hose port. See Fig 2. Using vacuum pump, apply 16 in. Hg to port. If vacuum bleeds off within 20 seconds, replace EVAP canister purge valve. If vacuum holds, go to next step. - 22) Check IAC Valve Function
Start engine and allow to idle. Ensure transmission is in Park or Neutral and engine is warmed to normal operating temperature. Disconnect IAC valve wiring harness connector. If engine speed drops or engine stalls, go to next step. If engine speed does not drop or engine does not stall, check throttle body for damage. If throttle body is okay, replace IAC valve. - 23) Check IAC Circuit For Short To Ground
Turn ignition off. Disconnect scan tool from DLC. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM connector pin No. 83 (IAC) and chassis ground. If resistance is more than 10,000 ohms and idle speed is normal, go to step 30). If resistance is more than 10,000 ohms and high idle speed is present, replace PCM. If resistance is 10,000 ohms or less, repair short to ground in IAC circuit.NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 23) to step 30). No test procedures have been omitted. - 30) Check IAC System For Intermittent Open Or Short Circuit
Connect scan tool to DLC. Start engine and allow to idle. Ensure all accessories are off and engine is warmed to normal operating temperature. Using scan tool, select IAC and RPM PIDs from PID/DATA monitor menu. IAC duty cycle should be 20-45 percent. Observe IAC and RPM PIDs for indication of fault while performing the following:- Wiggle and bend wiring harness starting at IAC valve and work toward PCM.
- Lightly tap on IAC valve to simulate road shock.
Fault will be indicated by sudden change in IAC PID or RPM PID value. If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be duplicated at this time. Go to TEST Z .
NOTE:
If DTC P0402 was output during self-test, service DTC prior to continuing with this test step.
NOTE:
EVAP canister is also referred to as carbon canister.