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, ensure following non-EEC related areas are not at fault:

• Brake light bulb.
• Brake light switch or brake light fuse.

1. 1) DTC P1703: (KOER) Verify Brake Pedal Was Depressed  DTC P1703 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:
   • Brake pedal not applied during self-test.
   • Brake pedal applied during entire self-test.
   • Open brake light circuit.
   • Short to ground or power.
   • Faulty brake light 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 step 3).

   • 2) DTC P1703: (KOEO)  DTC P1703 indicates that during KOEO SELF-TEST, voltage was seen on BOO test pin at PCM. Possible causes for this fault are:
     • Brake pedal applied during self-test.
     • Short to power.
     • Faulty brake light switch.

       If brake was applied during KOER SELF-TEST, repeat test. DO NOT  depress brake pedal during test. If pedal was not depressed, go to next step.

   • 3) DTC P0703 & P1703: Check Operation Of Brake Lights  With ignition on, check operation of brake lights. If brake lights operate normally, go to next step. If brake lights do not operate, go to step 5). If brake lights are always on, go to step 7).
   • 4) Check For BOO Circuit Cycling  Turn ignition off. Wait 10 seconds. Disconnect PCM 104-pin connector. Inspect terminals, and repair if damaged. Install breakout box, leaving PCM disconnected. Measure voltage between BOO test pin No. 92 and test pins No. 76 and 77 while applying and releasing brake. If voltage cycles, replace PCM. Remove breakout box and repeat QUICK TEST. If voltage does not cycle, repair open circuit in BOO switch circuit between PCM and BOO switch connection to brake light circuit. Repeat QUICK TEST.
   • 5) Check For Power To Brake Switch  Ensure related fuses and brake light bulbs are in good condition. Turn ignition off. Disconnect brake light switch (located on brake pedal). Measure voltage between BAT (+) input to brake light switch and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open BAT (+) circuit to brake light switch and repeat QUICK TEST.
   • 6) Verify Integrity Of Brake Switch  Disconnect brake light switch connector. Measure resistance between brake light switch terminals while depressing brake pedal. If resistance is less than 5 ohms, repair open circuit between brake light switch and brake light ground. Repeat QUICK TEST. If resistance is more than 5 ohms, replace brake light switch and repeat QUICK TEST.
   • 7) Verify Brake Switch Is Not Always Closed  Turn ignition off. Disconnect brake light switch (located on brake pedal). Turn ignition on. If brake lights are still on, go to next step. If brake lights are not on, verify correct installation of brake light switch. If installation is okay, replace brake light switch and repeat QUICK TEST.
   • 8) Check For Short To Power In PCM  Turn ignition off. Disconnect PCM. Turn ignition on. Check brake lights. If brake lights are on, go to next step. If brake lights are not on, replace PCM and repeat QUICK TEST.
   • 9) Check For Short To Power In Shift Lock Actuator  Turn ignition off. Ensure PCM and brake light switch are disconnected. Disconnect shift lock actuator, cruise control module, ABS module, and General Electronic Module (GEM) (if equipped). Turn ignition on. If brake lights are still on, repair short to power in BOO or stoplight circuit and repeat QUICK TEST. If brake lights are not on, repair short circuit in shift lock actuator circuit, cruise control system circuit, ABS circuit or general electronic module circuit. Repeat QUICK TEST.