LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2001 >> Prius >> Repair and Diagnosis (Single Page) >> Body & Frame >> Body, Cab Control Systems >> Body Control Systems >> System Tests >> Test No. 18: Body Electronic Control Unit Does Not Operate
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test No. 18: Body Electronic Control Unit Does Not Operate

  1. Check ECU-B fuse (7.5-amp), DOOR fuse (30-amp), GAUGE fuse (10-amp) and OBD-II fuse (7.5-amp). These fuses are located in fuse/relay box at driver's side of instrument panel. See Figure. Also, check DC/DC fuse (100-amp). This fuse is located in fusible link block in fuse/relay box at driver's side front corner of engine compartment, near strut tower. See Fig 1. If fuses are okay, go to next step. If any fuse is defective, repair short in wiring for appropriate fuse. See WIRING DIAGRAMS in POWER DOOR LOCKS & REMOTE KEYLESS ENTRY SYSTEMS - PRIUS article and ANTI-THEFT SYSTEMS - PRIUS article. For additional wiring for power supply circuit, see POWER DISTRIBUTION article in WIRING DIAGRAMS.
  2. Note location of body Electronic Control Unit (ECU). Body ECU is located at driver's side of instrument panel on the fuse/relay box and contains an 18-pin and 20-pin electrical connector. See Figure.
  3. Ensure ignition is off. Disconnect body ECU electrical connectors B8 and B9 at body ECU. See Figure.
  4. Using voltmeter, check voltage between body ECU electrical connector B8 terminal No. 11 (White/Blue wire) and electrical connector B9 terminal No. 1 (White/Black wire) at body ECU. See Figure. Also, check voltage between body ECU electrical connector B9 terminals No. 1 (White/Black wire) and No. 9 (Red/Green wire). See Figure. Voltage should be 10-14 volts. If voltage is not within specification, reinstall electrical connectors. Go to next step. If voltage is within specification, reinstall electrical connectors. Go to step  7.
  5. Check wiring harness and electrical connectors between body ECU electrical connector B9 terminal No. 1 (White/Black wire) at body ECU and ground connection. See WIRING DIAGRAMS in POWER DOOR LOCKS & REMOTE KEYLESS ENTRY SYSTEMS - PRIUS article. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary and recheck system operation.
  6. Check wiring harness and electrical connectors between battery and body ECU. See WIRING DIAGRAMS . It may be necessary to see WIRING DIAGRAMS in POWER DOOR LOCKS & REMOTE KEYLESS ENTRY SYSTEMS - PRIUS article and ANTI-THEFT SYSTEMS - PRIUS article. For additional wiring for power supply circuit, see POWER DISTRIBUTION article in WIRING DIAGRAMS. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary and recheck system operation.
  7. Check body ECU for proper voltage and input signals. See BODY ELECTRONIC CONTROL UNIT  under PIN VOLTAGE TESTS. If proper voltage and input signals exist, go to next step. If proper voltage and input signals do not exist, repair as necessary and recheck system operation.
  8. Replace body ECU with a known-good body ECU and recheck system operation. If system operates properly, original body ECU was defective. If system still does not operate properly, check wiring harness and electrical connectors for body ECU for an intermittent problem. Repair wiring harness or electrical connector as necessary.
    Fig 1: Locating DC/DC Fuse
    G00023155Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
scientia non olet · About LEMON Manuals