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Test B14 - Boo Switch

NOTE: Perform this test when Service Code 74 or 75 is displayed during QUICK TESTS or when directed here by other test procedures.

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

  1. Service Code 74: Verify Brake Pedal Was Depressed. If brake was NOT depressed during KOER SELF-TEST, repeat test and depress 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. Checking Power Circuit. Turn key 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 and 40 at breakout box, while applying and releasing brake. If voltage cycles, switch circuit is okay, replace ECA and repeat QUICK TEST. If voltage does not cycle, go to next step.
  3. Checking For Short To Ground. Turn key off. Leave breakout box installed and ECA disconnected. Set DVOM on 200K-ohm scale. Disconnect BOO circuit. Measure resistance between test pins No. 2 and 40 at the breakout box. If resistance is greater than 10K ohms, repair stoplamp circuit as necessary. If resistance is less than 10K ohms remove breakout box repair short, and repeat KOER SELF-TEST.
  4. Service Code 75: Cycle BOO Circuit. Turn key off, wait 10 seconds. Disconnect 60-pin connector. Check and repair wiring as necessary. Install breakout box leaving ECA disconnected. Set DVOM on 20-volt scale. Measure voltage between test pins No. 2 and 40 at the breakout box while depressing and releasing the brake pedal. If voltage cycles, remove breakout box. Replace ECA, and rerun QUICK TEST. If voltage does not cycle, go to next step.
  5. Checking BOO Circuit For Short To Power. Turn key off. Install breakout box, leaving ECA disconnected. Set DVOM on 20-volt scale. Disconnect BOO circuit connectors. Measure voltage between test pin No. 2 at the breakout box and engine block ground. If voltage is greater than one volt, remove breakout box, reconnect ECA and repair short circuit. Repeat KOER SELF-TEST. If voltage is less than one volt, go to next step.
  6. Check BOO Circuit Continuity. Turn key off. Install breakout box leaving ECA disconnected. Set DVOM on 200-ohms scale. Disconnect BOO harness connectors. Measure resistance between test pin No. 2 at breakout box and BOO signal at connector. If resistance is less than 5 ohms, fault is in lighting system stoplight circuit. Repair or replace as necessary. If greater than 5 ohms, remove breakout box, reconnect ECA, repair open circuit and repeat KOER SELF-TEST.
  7. Service Code 74: Verify Brake Pedal Was Depressed. Code 74 indicates that brake was NOT depressed during KOER SELF-TEST, the BOO signal did not cycle high and low. Repeat test and depress 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. If voltage did not cycle, repeat KOER SELF-TEST and depress brake pedal once during test.
  8. Checking BOO Circuit Cycling. Turn key 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 and 40 at breakout box while applying and releasing brake. If voltage cycles, switch circuit is okay, replace ECA and repeat QUICK TEST. If voltage does not cycle, go to next step.
  9. Checking Continuity of BOO Circuit. Turn key off. Leave breakout box installed and ECA disconnected. Set DVOM on 200-ohm scale. Disconnect BOO circuit connector. Measure resistance between test pin No. 2 at breakout box and BOO circuit harness connector (12A581). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, remove breakout box, reconnect ECA, repair open circuit, and repeat KOER SELF-TEST.
  10. Checking BOO Circuit For Short to Power. Turn key off. Install breakout box, leaving ECA disconnected. Set DVOM on 20-volt scale. Disconnect BOO circuit connector (12A581 to 14290 or 14401 Connectors). Measure voltage between test pin No. 2 at the breakout box and engine block ground. If voltage is greater than 1.0 volt, remove breakout box, reconnect ECA, repair short circuit, and repeat KOER SELF-TEST. If voltage is less than 1.0 volt, go to next step.
  11. Check BOO Circuit For Short to Ground. Turn key off. Leave breakout box installed and ECA disconnected. Set DVOM on 200K ohm scale. Disconnect BOO circuit connector (12A581 to 14290 or 14401 Connectors). Measure resistance between test pin No. 2 and test pin No. 40 at the breakout box. If resistance is greater than 10K ohms, repair stoplamp circuit as necessary. If resistance is less than 10K ohms remove breakout box repair short, and repeat KOER SELF-TEST.
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