Diagnostic Aids

Perform this test when directed by QUICK TEST. This test is intended to diagnose a faulty BOO switch circuit or ECA. To prevent replacement of good components, be aware following non-EEC related areas may be at fault:

• Brakelight bulb.
• Brakelight switch or brakelight fuse.

Application	Wire Color
Aerostar, Sable & Taurus	Red/Light Green
Escort 1.9L & Tracer 1.9L	Gray
All Others	Light Green

Application	Test Pin No.
Escort, Taurus 3.0L SHO & Tracer	5
Except Escort, Taurus 3.0L SHO & Tracer	2

1) Code 74/536: Verify Brake Pedal Was Depressed  Code 74/536 indicates that when brake pedal is depressed during KOER SELF-TEST  , BOO signal did not cycle high and low. Possible causes for this fault are:

• Brake pedal not depressed during self-test.
• Brake pedal pressed during entire self-test.
• Open brakelight circuit.
• Short to ground or power.
• Faulty ECA.

If brake was not depressed during KOER SELF-TEST, repeat test. Depress and release brake pedal only once during test. If pedal was depressed, go to step 2).

2) Check Operation Of Brakelights  With ignition on, check operation of brakelights. If brakelights operate normally, go to step 3). If brakelights do not operate, go to step 4). If brakelights are always on,go to step 5).

3) Check For BOO Switch Circuit Cycling  Turn ignition off. Wait 10 seconds. Disconnect ECA 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set DVOM on 20-volt scale. Measure voltage between test pins No. 2 or 5 and 40 while applying and releasing brake. If voltage cycles, replace ECA and repeat QUICK TEST  . If voltage does not cycle, repair open circuit in BOO switch circuit between ECA and BOO switch connection to brakelight circuit. Repeat QUICK TEST.

4) Check For Power To Brake Switch  Ensure related fuses and brakelight bulbs are in good condition. Turn ignition off. Disconnect brakelight switch (located on brake pedal). Measure voltage between BATT (+) input to brakelight switch and ground. If voltage is greater than 10 volts, check condition of brakelight switch. If brakelight switch is okay, repair open circuit between brakelight switch and brakelight ground. Repeat QUICK TEST  . If voltage is less than 10 volts, repair open BATT (+) circuit to brakelight switch and repeat QUICK TEST.

5) Verify Brake Switch Is Not Always Closed  Turn ignition off. Disconnect brakelight switch (located on brake pedal). Turn ignition on. If brakelights are still on, go to step 6). If brakelights are not on, verify correct installation of brakelight switch. If installation is okay, replace brakelight switch and repeat QUICK TEST  .

6) Check For Short To Power In ECA  Turn ignition off. Disconnect ECA. Turn ignition on, and check brakelights. If brakelights are on, go to step 7) (Cougar, Escort, Mustang, Thunderbird and Tracer with floor shift A/T) or repair short to power between ECA and harness connector (all other models). Repeat QUICK TEST  . If brakelights are not on, replace ECA and repeat QUICK TEST.

7) Check For Short To Power In Brake/Shift Interlock Solenoid  Turn ignition off. Disconnect brake/shift interlock solenoid. Turn ignition on. If brakelights are still on, repair short to power on BOO switch/brakelight circuit and repeat QUICK TEST  . If brakelights are not on, replace brake/shift interlock solenoid and repeat QUICK TEST.

10) Code 75/531  Code 75/531 indicates that while brake pedal was released during KOER SELF-TEST, BOO switch signal was high. Possible causes for this fault are:

• Brake pedal depressed during entire self-test.
• Open BOO switch/brakelight circuit (between ECA and brakelight ground).
• Short to POWER.
• Faulty brakelight switch.
• Faulty ECA.

Turn ignition on. Check brakelight operation. If brakelights operate normally, go to step 11). If brakelights are always on, go to step 5). If brakelights are off, inspect brakelight bulbs. If bulb is okay, repair open circuit between BOO switch connection to brakelight circuit and brakelight ground.

11) Check Continuity Of BOO Switch Circuit  Turn ignition off. Disconnect brakelight switch (located on brake pedal). Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Measure resistance between test pin No. 2 or 5 at breakout box and BOO switch terminal at switch wiring harness connector. If resistance is less than 5 ohms, replace ECA and repeat QUICK TEST  . If resistance is 5 ohms or more, repair open circuit between ECA and BOO switch connection to brakelight circuit and repeat KOER SELF-TEST  .

90) Continuous Memory Code 536  Code 536 indicates a BOO switch circuit failure. If BOO switch input does not cycle after a predetermined number of transitions from zero MPH to a specific speed, BOO switch input is presumed to be damaged and Code 536 is set. Possible causes for this code are:

• Brakelight switch improperly installed.
• Open brakelight/BOO switch circuit.
• Damaged brakelight switch.
• Poor brakelight ground connection.

Inspect brakelight switch for incorrect installation, poor alignment with pedal and damaged wiring. Repair if necessary. Clear codes, and repeat QUICK TEST  . If all components are in good condition, go to step 91).

91) Check Brakelight For Ground  Check brakelight connector and wires for corrosion and damage. If connector or wires are corroded or damaged, repair as necessary. Clear codes, and repeat QUICK TEST  . If brakelight connector and wires are okay, go to step 92).

92) Check BOO Switch Circuits For Short To Power  DO NOT depress brake pedal during this test. Turn ignition on. While watching brakelights, wiggle brakelight/BOO switch circuit wires and connectors. If brakelights flash, isolate and repair short to power. Clear codes, and repeat QUICK TEST  . If brakelights do not flash, go to step 93).

93) Check Brakelight Circuit Continuity  Turn ignition off. Depress and hold brake pedal. Observe brakelights. Tap brakelight switch to simulate road shock. Wiggle brakelight circuit wires and connectors. If brakelights blink or go off, isolate and repair open in brakelight circuit. Clear codes, and repeat QUICK TEST  . If brakelights are on constantly and do not blink or go off, go to step 94).

94) Check Continuity Of BOO Switch Circuit  Turn ignition off. Disconnect ECA 60-pin connector. Inspect and repair any damaged terminals. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 2 or 5 at breakout box and brakelight circuit at brakelight switch connector. While observing DVOM, wiggle BOO switch circuit wires and connectors. If resistance is 5 ohms or more, isolate and repair open circuit in BOO switch circuit. Remove breakout box, clear codes and repeat QUICK TEST  . If resistance is less than 5 ohms, fault cannot be duplicated at this time. Clear codes, and see SYMPTOMS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.