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High Altitude Control (HAC) Circuit

  1. The altitude switch is located on lower section of right firewall. With ignition on and engine stopped, disconnect altitude switch connector terminals "C" and "D." See Fig 1 . Check voltage at connector terminal "C". If voltage is less than 10 volts, go to step 3). If voltage is greater than 10 volts, check Black ground wire. If ground is incomplete, repair as necessary. If okay, go to step 2).
  2. Connect jumper wire from battery negative terminal to connector terminal "C". Ground and remove jumper wire repeatedly. HAC solenoid should click. If solenoid clicks, solenoid is okay. If solenoid does not click, check wiring. If wiring is okay, replace solenoid.
  3. Check for open or grounded Orange or Blue wires. If okay, remove ECM connector terminal No. 18 and check voltage to ground. If voltage is greater than 10 volts, replace ECM. If voltage is less than 10 volts, repair open or ground.
Fig 1: Wiring Diagram for High Altitude Control Circuit
G122345Courtesy of ISUZU MOTOR CO.
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