Diagnostic Aids

Perform this test when instructed by QUICK TEST or if directed by other test procedures. If engine is running rough or has rough idle, correct these conditions before performing test. Causes may be in ignition system, fuel system or EGR system. This test is terminals intended to diagnose:

RPM during SELF-TEST mode.
ISC solenoid.
Wiring harness circuits (ISC and VPWR).
ECA.

To prevent replacement of good components, be aware following non-EEC related areas may be at fault:

Engine temperature under or over correct operating range.
A/C input (electrical problem).
Incorrect idle speed or throttle stop adjustment.
Faulty cruise control linkage.

Fig 1: Idle Speed Control (Air By-Pass) Circuit

TEST PIN NO. 21 (ISC) WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Red/Light Green
Escort & Tracer	Blue/Orange
Probe	White/Red
Sable & Taurus 3.0L SHO & 3.8L	Orange/Black
Sable & Taurus 3.0L (Except SHO)	Brown/White
Continental, Crown Victoria, Grand Marquis, Mustang 2.3L, Tempo & Topaz	White
All Others	White/Light Blue

TEST PINS NO. 37 & 57 (VPWR) WIRE COLOR ID

Application	Wire Color
Escort & Tracer	White/Red
Probe	Red/Black
Except Escort, Probe & Tracer	Red

1) Code 12/412 Or 16 Code 12/412 indicates engine RPM could not be controlled within upper RPM limit during KOER SELF-TEST . Code 16 indicates engine RPM was too low to perform HEGO test during KOER SELF-TEST. Possible causes for this fault are:

Open or shorted circuit.
Sticking or binding throttle linkage.
Incorrect idle airflow setting.
Throttle body or ISC solenoid contaminated.
Faulty ISC solenoid.
Faulty ECA.
Mechanical faults unrelated to EEC-IV which could affect RPM.

Turn ignition off. Connect tachometer to engine. Start engine. Disconnect Idle Speed Control (ISC) harness. If RPM drops or engine stalls, go to step 2). If RPM does not drop or engine does not stall, go to step 3).

2) Check For EGR Codes If EGR service Code 31/327, 32/326/328, 33/332, 34/336/334 or 213 is displayed, reconnect ISC solenoid. Go to appropriate KOER SELF-TEST . See SERVICE CODE REFERENCE CHARTS. If these codes are not displayed, go to step 3).

3) Check For Other EEC-IV Codes If Code 22/126, 41/172, 42/173, 91/136 or 92/137 is displayed, reconnect ISC solenoid. Go to appropriate KOER SELF-TEST . See SERVICE CODE REFERENCE CHARTS . If these codes are not displayed, go to step 4).

4) Measure ISC Solenoid Resistance Turn ignition off. Disconnect ISC solenoid. Connect DVOM positive lead to VPWR terminal and negative lead to ISC terminal. See Fig 2 . Measure resistance of ISC solenoid. If resistance is not 6-13 ohms, replace ISC solenoid and repeat QUICK TEST . If resistance is 6-13 ohms, go to step 5).

Fig 2: ISC Solenoid Connector

5) Check For Internal Short To ISC Solenoid Case Turn ignition off. With ISC solenoid disconnected, measure resistance from either ISC terminal pin to ISC solenoid housing. If reading is more than 10,000 ohms, go to step 6). If reading is 10,000 ohms or less, replace ISC solenoid. Repeat QUICK TEST .

6) Check VPWR Circuit Voltage Leave ISC harness disconnected. Turn ignition on. Measure voltage between VPWR terminal at ISC harness connector and battery ground terminal. If voltage is 10.5 volts or more, go to step 7). If voltage is less than 10.5 volts, repair open in circuit and repeat QUICK TEST .

7) Check ISC Circuit Continuity Turn ignition off. Leave ISC solenoid disconnected. 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. 21 and ISC terminal at ISC wiring harness connector. If reading is 5 ohms or less, go to step 8). If reading is more than 5 ohms, repair open circuit. Reconnect components, and repeat QUICK TEST .

8) Check ISC Circuit For Short To Ground Turn ignition off. Leave ISC solenoid disconnected. Measure resistance between test pin No. 21 and test pins No. 40, 46 and 60. If any reading is less than 10,000 ohms, repair short to ground and repeat QUICK TEST . If all readings are 10,000 ohms or more, go to step 9).

9) Check ISC Circuit For Short To Power Turn ignition on. Measure voltage between breakout box test pin No. 21 and chassis ground. If voltage is more than 1.0 volt, repair short circuit. Reconnect all components, and repeat QUICK TEST . If code or symptom is still present, replace ECA. If voltage is 1.0 volt or less, go to step 10).

10) Check ISC Signal From ECA Turn ignition off. Reconnect ISC solenoid. Connect ECA to breakout box. Set DVOM on 20-volt scale. Connect DVOM between test pins No. 21 and 40 at breakout box. Start engine. Observe DVOM while slowly increasing engine speed to 3000 RPM. If DVOM voltage reading is 3.0-11.5 volts, go to step 11). If DVOM voltage reading is not 3.0-11.5 volts, remove ISC solenoid to confirm that it is not open. If ISC is okay, replace ECA and repeat QUICK TEST .

11) Check Base Idle Verify base idle speed is correct. See ADJUSTMENTS article in the ENGINE PERFORMANCE Section. If base idle speed is within specification, remove ISC solenoid and inspect for contamination. Repair or replace as necessary. Repeat QUICK TEST . If code or symptom is still present, replace ISC solenoid. If base idle speed is not correct, reset idle speed to specification. Repeat QUICK TEST. If unable to set idle to specification, go to step 12).

12) Check For Faults Affecting Idle Speed Check following mechanical items for faults:

Throttle linkage and/or cruise control linkage (sticking or binding).
Throttle body (contamination).
Vacuum hoses. Check Vehicle Emission Control Information (VECI).
Check for leaks around ISC solenoid (gaskets, etc.).

If all of these items are okay, remove ISC solenoid and inspect for contamination. Repair or replace as necessary. Repeat QUICK TEST . If code or symptom is still present, replace ISC solenoid. If any of these items are faulty, service as necessary. Remove breakout box. Reconnect components, and repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 15). No test procedures have been omitted.

15) Code 13/411 Code 13/411 indicates engine RPM could not be controlled within lower RPM limit during KOER SELF-TEST . Possible causes for this fault are:

Incorrect idle airflow setting.
Vacuum leaks.
Sticking or binding throttle linkage.
Throttle plates open.
Incorrect ignition timing (TFI ignition only).
Throttle body or ISC solenoid contamination.
ISC circuit shorted to ground.
Faulty ISC solenoid.

If above items are okay and idle is set to specification, remove ISC solenoid and inspect for contamination. Repair or replace as necessary. Repeat QUICK TEST . If code or symptom is still present, replace ISC solenoid. If idle speed is not set to specification, reset and repeat QUICK TEST. If idle speed cannot be set to specification, go to next step.

16) Check For Conditions Affecting Idle Speed Check following mechanical components:

Vacuum hoses. Check Vehicle Emission Control Information (VECI).
Throttle linkage and/or cruise control linkage (sticking or binding).
Induction system (vacuum leaks).
Throttle body (contamination).
Ensure throttle plates are fully closed.
Ensure CANP solenoid is not stuck open.
Ensure base ignition timing is to specification on emission decal (TFI vehicles only).

If everything checks okay, go to step 17). If fault is found, service as necessary and repeat QUICK TEST .

17) Check For Internal Short To ISC Solenoid Case With ignition off and ISC solenoid disconnected, set DVOM on 200-k/ohm scale. Measure resistance from either ISC terminal pin to ISC solenoid housing. If reading is more than 10,000 ohms, go to step 18). If reading is 10,000 ohms or less, replace ISC solenoid. Repeat QUICK TEST .

18) Check ISC Circuit For Short To Ground Turn ignition off. Leave ISC solenoid disconnected. 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. 21 and test pins No. 40, 46 and 60. If any reading is less than 10,000 ohms, repair short to ground. Reconnect components, and repeat QUICK TEST . If all readings are 10,000 ohms or more, go to step 19).

19) Check ISC Signal From ECA Turn ignition off. Connect ECA to breakout box. Reconnect ISC solenoid. Set DVOM on 20-volt scale. Connect DVOM between test pins No. 21 and 40. Start engine. Observe DVOM while slowly increasing and decreasing engine RPM. If voltage is 3.0-11.5 volts, remove ISC solenoid and inspect for contamination. Repair or replace as necessary, and repeat QUICK TEST . If code or symptom is still present, replace ISC solenoid. If voltage is not 3.0-11.5 volts, replace ECA and repeat QUICK TEST.