Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Pickup, 1995 Ford Econoline, 1995 Ford Club Wagon, and 1995 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

The MIL is turned on when PCM detects a fault in EEC circuit(s). The light will remain on as long as fault remains in system.

Perform this test only when instructed by QUICK TEST or if directed by CIRCUIT TEST QA. This test does not include procedure for models with electronic instrument panel. 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.
Faulty PCM.

Fig 1: Identifying Data Link Connector (DLC) Terminals (4.9L)

TEST PIN NO. 17 (STO/MIL) WIRE COLOR IDENTIFICATION

Application	Wire Color
All Models	Pink/Light Green

DATA + TEST PIN & WIRE COLOR IDENTIFICATION

Application ⁽¹⁾

Test Pin No.

Wire Color

MFI Models

Tan/Orange

SFI Models

Tan/Orange

⁽¹⁾	To determine if vehicle is equipped with MFI or SFI fuel system, see ENGINE/VIN ID article or appropriate WIRING DIAGRAM in WIRING DIAGRAMS .

DATA - TEST PIN & WIRE COLOR IDENTIFICATION

Application

Test Pin No.

Wire Color

MFI Models ⁽¹⁾

Pink/Light Blue

SFI Models ⁽¹⁾

Pink/Light Blue

⁽¹⁾	To determine if vehicle is equipped with MFI or SFI fuel system, see ENGINE/VIN ID article or appropriate WIRING DIAGRAM in WIRING DIAGRAMS .

1) Malfunction Indicator Light (MIL) Always On

If vehicle will not start, go to appropriate circuit test:

Go to CIRCUIT TEST AA.

Service all KOEO and continuous memory codes before proceeding with this test. Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pins No. 17 and 40 at breakout box. If resistance is more than 5 ohms, replace PCM and repeat QUICK TEST. If reading is 5 ohms or less, repair short between test pin No. 17 and Diagnostic Link Connector (DLC) terminal No. 17 or MIL. Reconnect all components, and repeat QUICK TEST.

2) 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 and ground side of MIL fuse. If voltage is more than 10.5 volts, go to step 4). If voltage is 10.5 volts or less, go to next step.

3) 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 on. If voltage is 10.5 volts or less, repair open MIL/B+ circuit. Verify repair by turning ignition on.

4) Check Voltage At B+ Circuit

Turn ignition on. Measure voltage between B+ side of MIL bulb socket and negative battery terminal. If voltage is 10.5 volts or less, repair open MIL circuit between fuse and bulb. Verify repair by turning ignition on. If voltage is more than 10.5 volts, go to next step.

5) 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 comes on, remove jumper wire, and go to next step. If MIL does not come on, remove jumper wire. Replace MIL bulb socket. Turn ignition on to verify correct MIL operation.

6) Check Continuity Of MIL Circuit

Turn ignition off. Disconnect 60-pin PCM connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 17 at breakout box and MIL wiring harness connector terminal. If resistance is less than 5 ohms, replace PCM. Turn ignition on to verify correct MIL operation. If resistance is 5 ohms or more, repair open ground side of MIL circuit. Turn ignition on to verify correct MIL operation.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 6) to step 10). No test procedures have been omitted.

10) MIL On Intermittently, Check For Intermittent Short From STO To Ground

If vehicle does not start, go to step 1). MIL 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 the following areas:

From Data Link Connector (DLC) to dash panel.
Dash panel to PCM.
Dash panel to Malfunction Indicator Light (MIL).

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

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 15). No test procedures have been omitted.

15) MIL Flashes With Erratic Idle

Symptoms indicate STI is grounded and PCM is performing self-test without tester installed. Turn ignition off. Disconnect 60-pin PCM connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between STI connector and engine ground. If resistance is less than 10,000 ohms, repair short circuit. Reconnect PCM, and turn ignition on to verify correct MIL operation. If resistance is 10,000 ohms or more, MIL circuit is okay. Verify symptom, and test for other rough idle symptoms.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 15) to step 20). No test procedures have been omitted.

20) CHECK ENGINE Message Displayed

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

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 20) to step 25). No test procedures have been omitted.

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 PCM or DCL circuit failure.
Code 533 indicates DCL 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 111-10-111), fault is in instrument cluster. If pass code is not displayed, service codes as necessary.