Diagnostic Aids

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

• Brakelight bulb.
• Brakelight switch or brakelight fuse.

Fig 1: BOO Switch Circuit

1. Step 1) DTC P1703: Verify Brake Pedal Was Depressed  This code indicates that when brake pedal is applied during KOER SELF-TEST , BOO signal did not cycle high and low. Possible causes for this fault are as follows:
   • Brake pedal not applied during self-test.
   • Brake pedal applied during entire self-test.
   • Open brakelight circuit.
   • Short to ground or power.
   • Faulty brakelight switch.
   • Faulty Powertrain Control Module (PCM).

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

2. Step 2) DTC P1703  This code indicates that voltage was present at BOO circuit during KOEO SELF-TEST . Possible causes for this fault are as follows:
   • Brake pedal applied during KOEO SELF-TEST .
   • BOO circuit short to power.
   • Faulty brakelight switch.

   If brake was applied during KOEO SELF-TEST , repeat test. If pedal was not depressed, go to next step.

3. Step 3) 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 5). If brakelights are always on,go to step 7).
4. Step 4) Check For BOO PID Cycling  Turn ignition off. Connect scan tester to DLC. Using scan tester, access BOO PID. Apply and release brake several times while observing BOO PID. If BOO PID voltage does not cycle on and off, go to step 10). If BOO PID voltage cycles, go to step 10) under CIRCUIT TEST Z.
5. Step 5) Check For Power To Brakelight Switch  Ensure related fuses and brakelight bulbs are in good condition. Turn ignition off. Disconnect brakelight switch (located on brake pedal). Measure voltage between B+ input to brakelight switch and ground. If voltage is more than 10 volts, go to next step. If voltage is less than 10 volts, repair open in B+ circuit to brakelight switch and repeat QUICK TEST .
6. Step 6) Check Brakelight Switch  With brakelight switch disconnected, measure resistance between switch terminals. If resistance is 5 ohms or more, replace brakelight switch and repeat QUICK TEST. If resistance is less than 5 ohms, repair open circuit between switch and stoplight ground and repeat QUICK TEST .
7. Step 7) 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 next step. If brakelights are not on, verify correct installation of brakelight switch. If installation is okay, replace brakelight switch and repeat QUICK TEST .
8. Step 8) Check For Short To Power In PCM  Turn ignition off. Disconnect PCM. Turn ignition on. Check brakelights. If brakelights are on, go to next step. If brakelights are off, replace PCM and repeat QUICK TEST .
9. Step 9) Check For Short To Power In Shift Lock Actuator  Turn ignition off. Ensure PCM and brakelight switch are disconnected. Disconnect shift lock actuator, cruise control module and ABS module (if equipped). Turn ignition on. If brakelights are still on, repair short to power in BOO circuit and repeat QUICK TEST . If brakelights are off, repair short circuit in shift lock actuator circuit, cruise control system circuit or ABS circuit. Reconnect all components and repeat QUICK TEST .
10. Step 10) Check For BOO PID Cycling  Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Using DVOM, measure voltage between test pin No. 92 and test pins No. 51 and 77 while applying and releasing brake. If voltage cycles on and off, replace PCM and repeat QUICK TEST . If voltage does not cycle, repair open in BOO circuit between PCM and BOO circuit connection splice to B+ circuit.