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Home >> Isuzu >> 2003 >> Axiom Base, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Fuel System >> Fuel System Electrical Test >> Testing Procedure
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Testing Procedure

  1. Perform On-Board Diagnostic II (OBD-II) System Check. See ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing OBD-II system check, go to next step.
  2. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Connect fuel pressure gauge as outlined in FUEL PUMP PRESSURE TEST  . Using scan tool, command fuel pump On. Fuel pressure should build up immediately. If fuel pressure builds up immediately, go to next step. If fuel pressure does not build up, go to step  4 .
  3. Verify fuel pump is not running by removing gas cap and listening for fuel pump motor. Using scan tool, command fuel pump On. If fuel pump runs for 2 seconds and turns off, fuel electrical system is operating properly. Testing is complete. If fuel pump does not run or runs continuously, go to step  12 .
  4. Turn ignition off. Remove fuel pump relay from underhood fuse/relay box. Using a test light connected to ground, probe battery feed to the relay. If test light illuminates, go to step  6 . If test light does not illuminate, go to next step.
  5. Repair open or short in battery feed to fuel pump relay. After repair, retest system.
  6. Connect a test light between fuel pump relay pull-in coil socket cavities. Turn ignition on. If test light illuminates for 2 seconds then turns off, go to step  12 . If test light does not illuminate, go to next step.
  7. Using test light connected to ground, probe PCM input to fuel pump relay socket cavity. Turn ignition on. If test light illuminates for 2 seconds and then turns off, go to next step. If test light does not illuminate, go to step  9 .
  8. Repair open in ground circuit between ground point and fuel pump relay. After repair, retest system.
  9. Check for open or short in PCM input to fuel pump relay. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. For PCM pin and terminal identification, see PIN VOLTAGE CHARTS article. If problem is found, repair as necessary. After repair, retest system. If no problem was found, go to next step.
  10. Check the fuel pump relay circuit for poor connection at the PCM. If a problem is found, replace terminal as necessary. Was a problem found? If yes, verify repair. If no, go to next step.
  11. Replace and reprogram PCM. See POWERTRAIN CONTROL MODULE REPLACEMENTunder POWERTRAIN CONTROL MODULE in appropriate SELF-DIAGNOSTICS article. Refer to latest Service Bulletin. Check to see if the latest software is released or not, Then Download the LATEST PROGRAMMED SOFTWARE to the replacement PCM. After repair, test drive vehicle to confirm repair.
  12. Install fuel pump relay. Disconnect fuel pump harness connector at fuel tank. Using a test light connected to ground, probe the fuel pump feed wire (harness side). Command the fuel pump ON with a Tech 2(R). If test light illuminates for 2 seconds, go to step  15 . If test light does not illuminate for 2 seconds, go to next step.
  13. Operate horn to verify horn relay is functional. Substitute horn relay for fuel pump relay. Repeat test procedure in step  12 . If test light does not illuminate for 2 seconds, go to next step. If test light does illuminate for 2 seconds, go to step  17 .
  14. Reconnect the horn relay in its proper location. Check for a short circuit, blown fuse or open circuit between the relay and the fuel tank. Is the action complete? Verify repair.
  15. With the fuel pump electrical connector at the fuel tank disconnected, connect a test light between the feed wire and the ground wire (harness side). Command the fuel pump ON with the Tech 2(R). Did the test light illuminate for 2 seconds. If yes, go to step  18 . If no, go to next step.
  16. Repair open circuit in fuel pump ground wire. After repair, test drive vehicle to confirm repairs.
  17. Re-connect the horn relay in its proper location. Replace the fuel pump relay. Is the action complete? After repair, test drive vehicle to confirm repairs.
  18. Replace fuel pump. See FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, test drive vehicle to confirm repair.
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