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DTC 79: Pressure Switch Circuit Malfunction

  1. Turn ignition switch to ON position, wait until pump motor stops running. Measure voltage between ABS-ECU connector E-105 terminal No. 17 and ground by backprobing connector. See Figure . If battery voltage is measured, go to next step. If measured voltage is 4 volts, go to step (7). If voltage is less than 2 volts, go to step  5 .
  2. Inspect Hydraulic Brake Booster (HBB) connector B-17 for corroded or damaged terminals. See Figure . If connector is damaged, repair connectors and then retest system for normal operation. If connector is okay, go to next step.
  3. Check Brown/Black wire between ABS-ECU connector E-106 and HBB connector B-17. See Figure . See WIRING DIAGRAMS  . Repair wiring as necessary, then retest system for normal operation. If wiring is okay, go to next step.
  4. Check Black wires between HBB connectors H-17 and H-18 and ground. Repair wiring as necessary, then retest system for normal operation. If wiring is okay, and problem persists, fault lies with pressure switches. Replace HBB unit. See HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. Retests system for normal operation.
  5. Disconnect Hydraulic Brake Booster (HBB) connector B-17. Turn ignition switch to ON position. Measure voltage between HBB connector B-17 terminal No. 5 (Brown/Black wire) and ground. See Figure . If measured voltage is 12 volts, pressure switch is faulty. Replace HBB unit. See HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. If measured voltage is not 12 volts, go to next step.
  6. Check Brown/Black wire between HBB connector B-17 and ABS-ECU. Repair wiring as necessary, then retest system for normal operation. If wiring is okay, and problem persists, replace ABS-ECU. See ELECTRONIC CONTROL UNIT (ABS ECU) under REMOVAL & INSTALLATION in ANTI-LOCK BRAKES - MONTERO article. Retest system for normal operation.
  7. Turn ignition switch to OFF position. Depress brake pedal at least 40 times, or until brake pedal can no longer be depressed. Turn ignition switch to ON position. Measure voltage between ABS-ECU connector E-106 terminal No. 43 (Brown/Green wire) and ground by backprobing connector. See Figure . If measured voltage is approximately 6 volts while pump motor is operating and less than 2 volts when pump motor is stopped, replace ABS-ECU. See ELECTRONIC CONTROL UNIT (ABS ECU) under REMOVAL & INSTALLATION in ANTI-LOCK BRAKES - MONTERO article. If voltage is less then 2 volts when pump motor is running and stopped, go to next step. If measured voltage is battery voltage, go to step  9 .
  8. Inspect ABS-ECU connector E-106 for corroded or damaged terminals. Repair connector as necessary, then retest system for normal operation. If connector is okay, and problem persists, replace ABS-ECU. See ELECTRONIC CONTROL UNIT (ABS ECU) under REMOVAL & INSTALLATION in ANTI-LOCK BRAKES - MONTERO article. Retest system for normal operation.
  9. Check HBB connector B-18 and ABS-ECU connector E-106 for damaged or corroded terminals. See Figure and Figure Repair connectors as necessary, then retest system for normal operation. If connectors are okay, go to next step.
  10. Check Brown/Green wire between ABS-ECU and HBB unit. See WIRING DIAGRAMS  . Repair wiring as necessary, then retest system. If wiring is okay and problem persists, pressure switch is faulty. Replace HBB. See HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. Retests system for normal operation.
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