Diagnostic Aids

Perform this test when directed by QUICK TEST.

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: brakelight bulb, brakelight switch or brakelight fuse. This test is intended to diagnose a faulty BOO circuit or ECA.

Application		Wire Color
Pin 2 (BOO)
Continental		Light Green
Sable & Taurus		Red/Light Green
Pin 40 (PWR GND)		Black/Light Green

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 as follows:

• Brake pedal not depressed during self-test
• Open brakelight circuit (BATT + side of BOO splice)
• 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. Depress and release brake pedal AFTER dynamic response code, but BEFORE brief WOT. If pedal was depressed, go to next step.

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

3) Check For BOO Circuit Cycling  Turn ignition off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, and loose wires. Install breakout box, 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, switch circuit is okay; replace ECA and repeat QUICK TEST. If voltage does not cycle, repair open circuit in BOO circuit between ECA and BOO connection to brakelight circuit.

4) Check For Power To Brake Switch  Ensure related fuses and brakelight bulbs are in good condition. Turn ignition off and wait 10 seconds. Disconnect brakelight switch (located on brake pedal). Set DVOM on 20-volt scale. Measure voltage between BATT (+) input to brakelight switch and chassis ground. If voltage is greater than 10 volts, verify operation of brakelight switch; if brakelight switch is okay, repair open circuit between brakelight switch and brakelight ground. Reconnect components and rerun QUICK TEST. If voltage is less than 10 volts, repair open BATT (+) circuit to brakelight switch. Reconnect all components and rerun QUICK TEST.

5) Verify Brake Switch Is Not Always Closed  With ignition off, disconnect brakelight switch (located on brake pedal). Turn ignition on, leaving engine off. If brakelights are still on, go to next step. If brakelights are not on, verify proper installation of brakelight switch. If installation is okay, replace brakelight switch. Reconnect all components and rerun QUICK TEST.

6) Check For Short To Power In ECA  Turn ignition off. Reconnect BOO circuit harness connector. Disconnect ECA. With ignition on and engine off, check if brakelights are on. If brakelights are on, go to next step (Cougar and Thunderbird with floor shift A/T). On all other models, repair short to power between ECA and harness connector; repeat QUICK TEST. If brake lights are not on, replace ECA and repeat QUICK TEST.

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

10) Code 75/531: Check For Operation Of Brake Lights  Code 75/531 indicates that while brake pedal was released during KOER SELF-TEST, BOO signal was high. Possible causes for this fault are as follows:

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

Turn ignition on. Check brakelight operation. If brakelights operate normally, go to next step. If brakelights are always on, go back to step 5). If brakelights are never on, inspect brakelight bulbs. If bulb is okay, repair open circuit between BOO connection to brakelight circuit and brakelight ground.

11) Check Continuity Of BOO Circuit  Turn ignition off. Install breakout box, leaving ECA disconnected. Set DVOM on 20O-ohm scale. Disconnect BOO circuit harness connector. Measure resistance between test pin No. 2 at breakout box and BOO circuit at harness connector. If resistance is less than 5 ohms, replace ECA; remover breakout box, reconnect all components and rerun QUICK TEST. If resistance is greater than 5 ohms, repair open circuit. Remove breakout box, reconnect all components and repeat KOER SELF-TEST.

90) Continuous Memory Code 536: Check For Proper Brakelight Switch Installation  Code 536 indicates a BOO circuit failure. If BOO input does not cycle after a predetermined number of transitions from 0MPH to a specific speed, BOO input is assumed to be damaged and code 536 is set. Possible causes for this code are as follows:

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

Inspect brakelight switch for proper installation (alignment with pedal), corrosion or damaged wiring. Repair any problems and rerun QUICK TEST. If all components are in good condition, go to next step.

91) Check Brakelight For Ground  Check brakelight ground connection for corrosion or other damage. Check brakelight connector and wires for corrosion or other damage. If brakelight wires, connector and connection are okay, go to next step. If wires, connector and connection are not okay, repair as necessary; clear codes and rerun QUICK TEST.

92) Check Brakelight/BOO circuits For Short To Power  Do not depress brake pedal during this test. Turn ignition on, leaving engine off. While watching brakelights, wiggle brakelight/BOO circuit wires and connectors. If brakelights do not flash, go to next step. If brakelights flash, isolate and repair short to power as necessary. Clear codes and rerun QUICK TEST.

93) Check Brakelight Circuit Continuity  With ignition off; depress and hold brake pedal. Wiggle brakelight circuit wires and connectors while observing brakelights. Tap brakelight switch to simulate road shock while observing brakelights. If brakelights are on constantly and do not blink or go off, go to next step. If brakelights blink or go off, isolate and repair open in brakelight circuit. Clear codes and rerun QUICK TEST.

94) Check Continuity Of BOO Circuit  Turn ignition off. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Install breakout box, leaving ECA disconnected. Set DVOM on 20O-ohm scale. Measure resistance between test pin No. 2 or No. 5 at breakout box and brakelight circuit at brakelight switch connector. While observing DVOM, wiggle BOO circuit wires and connectors. If resistance is ever greater than 5 ohms, isolate and repair open circuit in BOO circuit; remover breakout box, clear codes rerun QUICK TEST. If resistance is always less than 5 ohms, fault cannot be duplicated at this time. Clear codes and see INTERMITTENTS in the TESTS W/O CODES article in this section.