Diagnostic Aids
NOTE:
After each service or repair procedure has been completed, reconnect all components. Clear DTCs and repeat QUICK TEST procedures to ensure all EEC-V systems are working properly and DTCs are no longer present.
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 & VPWR)
- Faulty Idle Air Control (IAC) Valve
- Faulty Throttle Body
- Faulty Powertrain Control Module (PCM)
NOTE:
Proceed to DTC testing steps listed in FAULT CODE SETTING CONDITION table of fault code setting condition.
FAULT CODE SETTING CONDITION
| Fault Code | KOEO | KOER | Continuous Memory |
|---|---|---|---|
| P0505 | KE2 | ||
| P1504 | KE2 | KE2 | KE2 |
| P1506 | KE20 | ||
| P1507 | KE2 | KE2 |
- 1) Idle Problem Or Engine Stalls: Perform KOER On-Demand Self-Test For Continuous Memory DTCs
Retrieve and record all Continuous Memory DTCs. Perform KOER ON-DEMAND SELF-TEST . If unable to complete KOER ON-DEMAND SELF-TEST, go to next step. If KOER ON-DEMAND SELF-TEST is complete and DTC P0505, P1504 or P1507 is present, go to next step. If DTC P0505, P1504 or P1507 are not present, IAC system is okay and testing is complete. If symptom still exists, return to SYMPTOMS under TROUBLE SHOOTING - NO CODES - EEC-V (GASOLINE) article. - 2) DTC P0505, P1504 & P1507, Or Starts Only At Part Throttle: Check VPWR Voltage To IAC Valve
DTC P0505 indicates PCM attempted to control engine idle speed and desired RPM could not be reached or controlled during self-test. DTC P1504 indicates PCM detects an electrical load failure on IAC output circuit. DTC P1507 indicates that PCM detects engine idle speed is less than desired RPM. Possible causes are.- IAC Circuit Open, Or Shorted To GND Or VPWR
- VPWR Circuit To IAC Valve Open
- Air Inlet Plugged
- Damaged IAC Valve
- Faulty PCM
Turn ignition switch to OFF position. Disconnect IAC valve connector. Turn ignition switch to ON position. Measure voltage between VPWR terminal at IAC valve harness connector and ground. See Fig 1 or Fig 2 . 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 switch to OFF position. Using a DVOM, measure resistance between both IAC valve terminals. If resistance is 6-13 ohms, go to next step. If resistance is not 6-13 ohms, replace IAC valve. - 4) Check IAC Valve For Internal Short To IAC Case
Ensure ignition switch is turned to OFF position. Using a DVOM, measure resistance between each IAC valve terminal and IAC valve housing. If both resistance measurements are more than 10 k/ohms for DTC P1504, go to step 7). If both resistance measurements are more than 10 k/ohms for all other DTCs, go to next step. If any resistance measurement is 10 k/ohms or less, replace IAC valve. - 5) Check For Plugged Air Inlet
Turn ignition switch to OFF position. Remove air filter. Inspect air filter, Mass Airflow (MAF) sensor and air inlet system for excessive dirt or contamination. Repair as necessary. If air inlet system is okay, reinstall inlet air system and go to next step. - 6) Check For Vacuum Leaks
Start engine and allow to idle. Listen for vacuum leaks. Inspect air inlet system from MAF sensor to intake manifold for any of the following possible faults.- Cracked Or Punctured Air Inlet Tube
- Loose Inlet Air Tube, IAC Tubes Or Air Cleaner Housing
- Loose Or Damaged Throttle Body
- Contaminated Or Damaged IAC Valve, Or Gasket
- Faulty EGR Valve Or Gasket
- Damaged Vacuum Supply Connector Or Hose(s)
- Faulty PCV Valve, Connector 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 For Open In Harness
Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect IAC valve connector. Using a DVOM, measure resistance of IAC circuit between PCM harness connector and IAC valve harness connector. See Fig 1 or Fig 2 . 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 VPWR In Harness
Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector IAC terminal and negative battery terminal. If voltage is one volt or more, repair short to VPWR in IAC circuit. If voltage is less than one volt, go to next step. - 9) Check IAC Circuit For Short To Ground
Turn ignition switch to OFF position. Disconnect scan tool from DLC. On LS, measure resistance between PCM connector terminal C9 (IAC) and terminals No. A24, A25, A26 and A27 (PWR GND). On all other models, measure resistance between PCM connector terminal No. 83 (IAC) and terminals No. 51 and 103 (PWR GND). If resistance is more than 10 k/ohms and DTC P1504 was set, replace PCM, or go to next step for all others. If resistance is 10 k/ohms or less, repair short to ground in IAC circuit. - 10) Check IAC Signal From PCM
Reconnect PCM harness connector. Reconnect IAC valve connector. Start engine and allow it to idle. If engine stalls, place a shim under hard stop screw to maintain idle conditions. Using scan tool, select IAC and RPM PIDs from PID/DATA MONITOR & RECORD 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 IAC 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 value is not within specification at closed throttle or duty cycle does not respond to RPM change, replace IAC valve (DTC P1507) or replace PCM (all others). If IAC PID value is within specification at closed throttle and duty cycle does respond to RPM change, 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: Check For Vacuum Leaks
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 switch to OFF position. Disconnect hoses from EVAP canister purge valve. Connect a vacuum pump to carbon canister hose port. See Fig 3. 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 For Proper 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 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. Repair or replace as necessary. If throttle body is okay, replace IAC valve. - 23) Check IAC Circuit For Short To Ground
Turn ignition switch to OFF position. Disconnect scan tool from DLC. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM connector terminal No. 83 (IAC) and chassis ground. If resistance is more than 10 k/ohms and idle speed is normal, go to step 30). If resistance is more than 10 k/ohms and high idle speed is present, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . If resistance is 10 k/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
Connect scan tool to Data Link Connector (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 & RECORD menu. IAC duty cycle should be 20-45 percent. Observe IAC and RPM PIDs for indication of fault while performing the following:- Shake, wiggle and bend wiring harness starting at IAC valve and work toward PCM.
- Lightly tap on IAC valve and wiggle connector 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 and an idle quality, starting or stalling symptom is present, replace IAC valve. If no faults are found and no symptoms are present, problem cannot be duplicated at this time. Go to TEST Z .
NOTE:
Step 1) is performed when directed here from SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V (GASOLINE) article.
NOTE:
If EGR DTC P0402 was output during KOER ON-DEMAND SELF-TEST, service DTC P0402 prior to continuing with this test step.
NOTE:
EVAP canister is also referred to as carbon canister.