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A/C-Cut Control System Circuit: Prius

WARNING: Read service precautions before proceeding with service procedure. See SERVICE PRECAUTIONS .
  1. If Toyota hand-held tester is available, go to next step. If Toyota hand-held tester is not available, go to step  7.
  2. Connect hand-held tester to data link connector No. 3 at driver's side of instrument panel. See Figure. Turn ignition on and then turn hand-held tester on. Start engine and turn A/C switch to ON position. Ensure A/C clutch engages.
  3. Select ACTIVE TEST MODE on hand-held tester. Check operation of A/C clutch when A/C-cut control is operated by hand-held tester. A/C clutch should turn off (stop operating) when A/C-cut control is operated by hand-held tester. If A/C clutch does not operate properly, go to next step. If A/C clutch operates properly, shut engine off. Remove hand-held tester. Diagnose by symptom. See TROUBLE SHOOTING - NO CODES article.
  4. Check for open and short in wiring harness and electrical connectors between Engine Control Module (ECM) and A/C amplifier. See WIRING DIAGRAMS in appropriate article in AIR CONDITIONING & HEATING. ECM is located behind glove box. See Fig 1. A/C amplifier is attached to rear of center cluster module control. See Fig 1. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary.
    Fig 1: Locating Engine Control Module & A/C Amplifier (Prius)
    G00016730Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  5. Remove ECM with electrical connectors still attached. See ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  6. Note ECM electrical connector terminals. See Figure. Start engine. Using voltmeter, check voltage between body ground and terminal No. 22 (Pink/Green wire) at ECM electrical connector E10 while turning A/C switch from ON to OFF positions. This is the ACT terminal at ECM. Voltage should be 9-14 volts with A/C switch in ON position and less than 1.5 volts with A/C switch in OFF position. If voltage is not as specified, replace A/C amplifier. If voltage is as specified, check ECM ground circuit. See WIRING DIAGRAMS article. If ECM ground circuit is defective, repair ground circuit as necessary. If ECM ground circuit is okay, replace ECM.
  7. Remove ECM with electrical connectors still attached. ECM is located behind glove box. See Fig 1. See ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  8. Note ECM electrical connector terminals. See Figure. Start engine. Using voltmeter, check voltage between body ground and terminal No. 22 (Pink/Green wire) at ECM electrical connector E10 while turning A/C switch from ON to OFF positions. This is the ACT terminal at ECM. Voltage should be 9-14 volts with A/C switch in ON position and less than 1.5 volts with A/C switch in OFF position. If voltage is not as specified, go to next step. If voltage is as specified, check ECM ground circuit. See WIRING DIAGRAMS article. If ECM ground circuit is defective, repair ground circuit as necessary. If ECM ground circuit is okay, replace ECM.
  9. Check for open and short in wiring harness and electrical connectors between ECM and A/C amplifier. See WIRING DIAGRAMS in appropriate article in AIR CONDITIONING & HEATING. A/C amplifier is attached to rear of center cluster module control. See Fig 1. If wiring harness and electrical connectors are okay, replace A/C amplifier. If wiring harness or electrical connector is defective, repair as necessary.
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