Diagnostic Aids

Perform this test only when instructed by QUICK TEST or if directed by CIRCUIT TEST QA. This circuit test does not apply to vehicles with electronic instrument cluster. To prevent replacing good components, be aware that fuse, bulb or bulb socket may be cause of problem. This test is only intended to diagnose:

• STO/MIL circuit.
• ECA.

Application	Pin No.	Wire Color
Ranger	17 (STO/MIL)	Pink/Lt. Green
Ranger	28 (DATA +)	Tan/Orange
Ranger	9 (DATA -)	Pink/Lt. Blue

1) Malfunction Indicator Light (MIL) Always On  If vehicle will not start, go to appropriate circuit test:

• For TFI, CIRCUIT TEST AA.
• For DIS, CIRCUIT TEST AB.
• For EDIS, CIRCUIT TEST AC.

Service all KOEO and Continuous Memory Codes before proceeding with this test. 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 pins No. 17 and 40 at breakout box. If resistance is more than 5 ohms, replace ECA and repeat QUICK TEST. If resistance is 5 ohms or less, repair short between test pin No. 17 and self-test connector or between test pin No. 17 and MIL light. Reconnect all components, and repeat QUICK TEST.

4) Malfunction Indicator Light (MIL) Does Not Light  If vehicle will not start, go to step 1). Turn ignition on. Measure voltage between negative battery terminal to ground side of MIL fuse. If voltage is more than 10.5 volts, go to step 6). If voltage is 10.5 volts or less, go to step 5).

5) Check For Voltage At Fuse  Turn ignition on. Measure voltage from negative battery terminal to power side of MIL fuse. If voltage is more than 10.5 volts, replace fuse. Verify repair by turning ignition switch to RUN position. If voltage is 10.5 volts or less, repair open MIL/VBAT circuit. Verify repair by turning ignition switch to RUN position.

6) Check Voltage At VBAT Circuit  Turn ignition on. Measure voltage between VBAT side of MIL bulb and negative battery terminal. If voltage is 10.5 volts or less, repair open in MIL circuit between fuse and bulb. Verify repair by turning ignition switch to RUN position. If voltage is more than 10.5 volts, go to step 7).

7) Check MIL Bulb Response To Grounding  Turn ignition off. Attach jumper wire between ground side of MIL bulb socket and chassis ground. Turn ignition on. If MIL light comes on, turn ignition off. Remove jumper wire, and go to step 8). If MIL light does not come on, turn ignition off and remove jumper wire. Replace MIL bulb socket. Turn ignition on to verify correct MIL operation.

8) Check Continuity Of MIL 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. 17 at breakout box and MIL terminal at wiring harness connector. If resistance is less than 5 ohms, replace ECA. If resistance is 5 ohms or more, repair open MIL circuit. Turn ignition on to verify correct MIL operation.

10) MIL On Intermittently, Check For Intermittent Short From STO To Ground  If vehicle does not start, go to step 1). Light comes on when a fault code is present. Service all fault codes before proceeding. If no codes are output, proceed with this test. Enter KOEO wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. Check DVOM for indication of fault while performing wiggle test on harness in following areas:

• From self-test connector to dash panel.
• Dash panel to ECA.
• Dash panel to Malfunction Indicator Light (MIL).

If a fault is indicated, repair as necessary and repeat QUICK TEST. If a fault is not indicated, fault cannot be duplicated at this time. Testing is complete.

15) MIL Flashes With Erratic Idle  Symptoms indicate STI is grounded and ECA is performing self-test without tester installed. 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 STI connector and engine block ground. If resistance is 10,000 ohms or less, repair short circuit. Reconnect ECA, and turn ignition on to verify correct MIL operation. If resistance is more than 10,000 ohms, MIL circuit is okay. Verify symptom, and test for other rough idle symptoms.

20) CHECK ENGINE Message Displayed  If vehicle will not start, go to step 1). Perform KOEO SELF-TEST. If result is Code 11-10-11 or Code 111-10-111 (pass code), fault is in instrument cluster. If pass code is not displayed, service codes as necessary.

25) Continuous Memory Code 529 Or 533: CHECK ENGINE Or CHECK DCL Message Displayed  Codes 529 and 533 indicate circuit fault has occurred on Data Communications Link (DCL). These codes can occur alone or with another code. Fault will occur under following conditions:

• Code 529 indicates ECA or Data Communicator Link (DCL) circuit failure.
• Code 533 indicates Data Communication Link to Electronic Instrument Cluster circuit failure.

If vehicle does not start, go to step 1). If vehicle starts, clear continuous memory codes. Wait 5 minutes, and repeat KOEO SELF-TEST. If result is pass code (Code 11-10-11 or 111-10-111), fault is in instrument cluster. If pass code is not displayed, service codes as necessary.