Diagnostic Aids

Perform this test only when instructed by QUICK TEST or directed here by a driveability symptom. This test is only intended to diagnose:

• Wiring harness circuits (VPWR and IAC).
• Intake Air Control (IAC) assembly.
• ECA.

To prevent replacing good components, check following non-EEC areas for faults:

• Vacuum tank leaks.
• Vacuum hose leaks.

1) Code 81/551: Check IAC Solenoid Resistance  Code 81/551 indicates IAC solenoid output voltage did not change when IAC was activated during KOEO SELF-TEST  . Possible causes for this fault are:

• IAC circuit open or shorted.
• IAC solenoid disconnected.
• ECA output driver open or grounded.

Turn ignition off. Disconnect IAC solenoid connector from wiring harness. Measure resistance between IAC solenoid terminals. See Fig 2 . If resistance is not 50-100 ohms, replace solenoid and repeat QUICK TEST  . If resistance is 50-100 ohms, go to step 2).

2) Check Voltage Of VPWR Circuit  Turn ignition on. Measure voltage between VPWR circuit of IAC solenoid wiring harness connector and negative battery terminal. If voltage is more than 10.5 volts, go to step 3). If voltage is 10.5 volts or less, repair open circuit in wiring harness and repeat QUICK TEST  .

3) Check Continuity Of IAC Solenoid Circuit  Turn ignition off. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Measure resistance between test pin No. 32 at breakout box and IAC terminal of IAC solenoid wiring harness connector. If resistance is 5 ohms or less, go to step 4). If resistance is more than 5 ohms, repair open circuit. Reconnect all components, and repeat QUICK TEST  .

4) Check For Short To Ground  Turn ignition off. With breakout box installed and ECA disconnected, measure resistance between test pin No. 32 and test pins No. 40, 46 and 60 at breakout box. If resistance is 100,000 ohms or more, go to step 5). If resistance is less than 100,000 ohms, repair short circuit and repeat QUICK TEST  .

5) Check IAC Circuit For Short To Power  Turn ignition off. Measure resistance between test pin No. 32 and test pins No. 37 and 57 at breakout box. If resistance is 100,000 ohms or more, replace ECA. Reconnect components, and repeat QUICK TEST  . If resistance is less than 100,000 ohms, repair short circuit and repeat QUICK TEST. If fault is still present, replace ECA.

6) Check Front & Rear Intake Air Valves  Turn ignition off. Disconnect vacuum lines from both intake air valves. See Fig 3 . Use vacuum pump to apply 10 in. Hg vacuum to each air valve. If both valves hold vacuum, go to step 7). If valves do not hold vacuum, replace valves as necessary and repeat QUICK TEST  .

7) Check Operation Of Intake Air Valves  Turn ignition off. Apply 10 in. Hg to each air valve. If both valves and mechanical linkage move in response to applied vacuum, go to step 8). If valves and/or linkage do not move, repair as necessary and repeat QUICK TEST  .

8) Check Vacuum To Both Intake Air Valves  Turn ignition off. Check vacuum lines from air valves to IAC solenoid. See Fig 4 . Inspect vacuum lines for damage and blockage. If vacuum lines are damaged or blocked, repair as necessary. If vacuum lines are okay, go to step 9).

9) Check Vacuum Source To IAC Solenoid  Disconnect IAC solenoid vacuum supply hose from intake manifold. See Fig 5 . Start engine. Check vacuum at disconnected hose. If vacuum is present at hose, replace IAC solenoid and repeat QUICK TEST  . If vacuum is not present, check supply hose to IAC solenoid. Repair as necessary, and repeat QUICK TEST.