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Engine Control Module Power Source Circuit: Corolla

  1. Remove necessary components for access to Engine Control Module (ECM). See ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  2. Remove bolts from ECM so electrical connectors can be accessed on ECM. Note ECM electrical connector terminals. See Figure and Figure .
  3. Turn ignition on. On 3-speed A/T and M/T models, using voltmeter, check voltage between terminals No. 12 (Black wire) at ECM electrical connector E6 and No. 14 (Brown wire) at ECM electrical connector E4. On 4-speed A/T, using voltmeter, check voltage between terminals No. 16 (Black wire) at ECM electrical connector E10 and No. 17 (Brown wire) at ECM electrical connector E8. On all models, this is the +B and E1 terminals at ECM. Voltage should be 9-14 volts. If voltage is within specification, diagnose by symptom. See TROUBLE SHOOTING - NO CODES article. If voltage is not within specification, check for open in wiring harness and electrical connectors between terminal No. 14 (Brown wire) at ECM electrical connector E4 and body ground on 3-speed A/T and M/T models, or terminal No. 17 (Brown wire) at ECM electrical connector E8 and body ground on 4-speed A/T models. See WIRING DIAGRAMS article. On all models, if wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary.
  4. Check operation of EFI main relay. See EFI MAIN RELAY  under MODULES, MOTORS, RELAYS & SOLENOIDS. EFI main relay may also be referred to as EFI relay or F-HTR relay. If EFI main relay operates properly, go to next step. If EFI main relay is defective, replace EFI main relay.
  5. Check for defective EFI fuse. EFI fuse may also be referred to as F-HTR fuse. EFI fuse is located in fuse/relay box at driver's side front corner of engine compartment, just in front of strut tower. If EFI fuse is okay, go to next step. If EFI fuse is defective, repair short in wiring harness and components connected to EFI fuse. See WIRING DIAGRAMS article.
  6. Check for open in wiring harness and electrical connectors between EFI main relay and battery, and between EFI main relay and ECM. See WIRING DIAGRAMS article. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary.
  7. Check for defective IGN fuse. IGN fuse is located in fuse/relay box behind driver's side of instrument panel. If IGN fuse is okay, go to next step. If IGN fuse is defective, repair short in wiring harness and components connected to IGN fuse. See WIRING DIAGRAMS article.
  8. Check ignition switch. See IGNITION SWITCH  under ENGINE SENSORS & SWITCHES. If ignition switch is okay, go to next step. If ignition switch is defective, replace ignition switch. See IGNITION SWITCH under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  9. Check for open in wiring harness and electrical connectors between ignition switch and EFI main relay, and between body ground and EFI main relay. See WIRING DIAGRAMS article. If wiring harness and electrical connectors are okay, test is complete. If wiring harness or electrical connector is defective, repair as necessary.
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