Diagnostic Aids

Perform this test when directed by QUICK TEST. This test is intended to diagnose ECA and BOO circuit.

Fig 1: Brake On-Off (BOO) Switch Circuit

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

Brake pedal not depressed and released during KOER SELF -TEST.
Brake pedal depressed during entire KOER SELF-TEST.
Faulty ECA.
Faulty brake switch.
Open BOO/brakelight circuit.
Short to ground or power.

If brake pedal was depressed, go to next step. If brake pedal 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.

2) Check Operation Of Brakelights - Turn 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. Disconnect and inspect ECA 60-pin connector. With breakout box installed, disconnect ECA. Set DVOM on 20-volt scale. Measure voltage between pin No. 2 of BOO vehicle harness connector and pin No. 40 at breakout box while depressing and releasing brake pedal. If voltage cycles, replace ECA. Remove breakout box, and rerun QUICK TEST . If voltage does not cycle, repair open in BOO circuit between ECA and BOO connection to brakelight circuit. Rerun 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 chassis ground. If voltage is more than 10 volts, verify operation of brakelight switch. If brakelight switch is okay, repair open in circuit between brakelight switch and brakelight ground. Reconnect brakelight switch connector, and rerun QUICK TEST . If voltage is less than 10 volts, repair open BATT (+) circuit to brakelight switch. Reconnect brakelight switch connector, and rerun QUICK TEST .

5) Verify Brake Switch Is Not Always Closed - Turn ignition off. Disconnect brakelight switch. Disconnect ECA. Turn ignition on, leaving engine off. If brakelights are still on, repair short to power in Boo/brakelight circuit. Reconnect all components, and rerun QUICK TEST . If brakelights are not on, replace ECA. Reconnect brakelight switch connector, and rerun QUICK TEST .

6) Check For Short To Power In ECA - Turn ignition off. Disconnect brakelight switch connector. Disconnect ECA. Turn ignition on, leaving engine off. If brakelights are still on, repair short to power in Boo/brakelight circuit. Reconnect all components, and rerun QUICK TEST . If brakelights are not on, replace ECA. Reconnect brakelight switch connector, and rerun QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Test skips from step 6) to step 10). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

10) Code 75/532: Check For Operation Of Brakelights - Code 75/531 indicates that BOO signal was high while brake pedal was released during KOER SELF-TEST. Possible causes for this fault are as follows.

Brake Pedal Depressed During Entire KOER SELF-TEST
Faulty Brakelight Switch
Faulty ECA
Open BOO/Brakelight Circuit (Between ECA And Brakelight Ground)
Short To POWER

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

11) Check Continuity Of BOO Circuit - Turn ignition off. Disconnect and inspect ECA 60-pin connector. With breakout box installed, disconnect ECA. Disconnect brakelight switch connector. Measure resistance between test pin No. 2 at breakout box and brakelight switch vehicle harness connector terminal. If resistance is less than 5 ohms, replace ECA. Remove breakout box, reconnect brakelight switch connector and rerun QUICK TEST . If resistance is greater than 5 ohms, repair open in circuit between BOO connection to brakelight circuit and ECA. Remove breakout box, reconnect ECA and brakelight switch connector, and repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Test skips from step 11) to step 90). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

90) Continuous Memory Code 536: Check for Proper Brakelight Switch Installation - Code 536 indicates a BOO circuit failure. BOO input has failed if BOO input does not cycle after a predetermined number of transactions from zero MPH to a specific speed. Possible causes for this fault are as follows.

Brakelight/BOO Circuit Shorted To Power
Brakelight Switch Improperly Installed
Faulty Brakelight Switch
Faulty Brakelight Ground
Open Brakelight/BOO Circuit

Check brakelight switch for damage and proper installation. If brakelight switch is okay, go to next step. If brakelight switch is not okay, repair as necessary. Clear continuous memory, and rerun QUICK TEST .

91) Check Brakelight Ground - Check brakelight ground connections for damage. Check brakelight connector, terminals and wire for damage. If brakelight ground connections, connector, terminals and wires are okay, go to next step. If brakelight ground connections, connector, terminals and wires are not okay, repair as necessary. Clear continuous memory, and rerun QUICK TEST .

92) Check Brakelight/BOO Circuits For Short To Power - Turn ignition on, leaving engine off. DO NOT depress brake pedal. Wiggle brakelight/BOO circuit wires and connectors. Observe brakelights. If brakelights do not flash on while wiggling wires and connectors, go to next step. If brakelights flash on while wiggling wires and connectors, isolate short to power and repair as necessary. Clear continuous memory, and rerun QUICK TEST .

93) Check Brakelight Circuit Continuity - Turn ignition off. Depress and hold brake pedal. Wiggle brakelight circuit wires and connectors. Observe brakelights. Lightly tap brakelight switch to simulate road conditions. Observe brakelights. If brakelights do not go off, go to next step. If brakelights go off, isolate open in brakelight circuit and repair as necessary. Clear continuous memory, and rerun QUICK TEST .

94) Check BOO Circuit Continuity - Turn ignition off. Release brake pedal. Disconnect and inspect ECA 60-pin connector. With breakout box installed, disconnect ECA. Connect DVOM between BOO test pin No. 2 at breakout box and brakelight circuit at brakelight switch. Set DVOM on 200-ohm scale. Wiggle BOO circuit connectors. Observe DVOM. If resistance is never greater than 5 ohms while wiggling connectors, go to INTERMITTENTS in TESTS W/O CODES article. If resistance is ever greater than 5 ohms while wiggling connectors, isolate open in BOO circuit and repair as necessary. Remove breakout box, reconnect ECA and rerun QUICK TEST .