1998 Infiniti QX4FACTORY OEM SERVICE PROCEDURE

Powertrain Control Module (Pcm): Frontier

  1. Start engine. If engine starts, go to step 6). If engine does not start, go to next step.
  2. Turn engine off and leave ignition on. Using DVOM, measure voltage between PCM harness connector terminal No. 24 (White/Green wire) and ground by backprobing connector. See Figure. If battery voltage is present, go to next step. If battery voltage is not present, repair blown fuse or open or short in White/Green wire between fuse block and PCM.
  3. Turn ignition off. Disconnect PCM harness connector. Using DVOM, check continuity between ground and PCM harness connector terminals No. 10, 19, 25, 32, 116 and 124. See Figure. If continuity exists on all wires, go to next step. If continuity does not exist on any wire, repair open in appropriate wire. See WIRING DIAGRAMS article.
  4. Disconnect ECCS relay (located next to PCM). Turn ignition on. Using DVOM, measure voltage between ground and ECCS relay harness connector terminals No. 2 and 5. See Figure. If battery voltage exists, go to next step. If battery voltage does not exist, repair blown fuse or open or short in appropriate wire.
  5. Turn ignition off. Check continuity between PCM harness connector terminal No. 4 and ECCS relay harness connector terminal No. 1 (Light Green/Red wire). See Figure & Figure . If continuity exists, go to step 13). If continuity does not exist, repair open or short in Light Green/Red wire.
  6. Turn ignition on. Using DVOM, measure voltage between ground and PCM harness connector terminal No. 80 (Light Blue wire) by backprobing connector. If battery voltage is present, go to next step. If battery voltage is not present, repair blown fuse or open or short in Light Blue wire between fuse block and PCM.
  7. Turn ignition off. While turning ignition on then off, measure voltage between ground and PCM harness connector terminals No. 67, 72 and 117 by backprobing connector. Battery voltage should exist with ignition on and for a few seconds after ignition is turned off. If voltage is as specified, go to step 12). If battery voltage does not exist, go to next step. If battery voltage exists for more than a few seconds after ignition is turned off, go to step 11).
  8. Turn ignition off. Disconnect PCM harness connector. Disconnect ECCS relay (located next to PCM). Using DVOM, check continuity between ECCS harness connector terminal No. 3 and PCM harness connector terminals No. 67, 72 and 117. See Figure & Figure . If continuity exists on both wires, go to next step. If continuity does not exist on either wire, repair open or short in appropriate wire. See WIRING DIAGRAMS article.
  9. Turn ignition on. Using DVOM, measure voltage between ground and ECCS relay harness connector terminals No. 2 and 5. See Figure. If battery voltage exists, go to next step. If battery voltage does not exist, repair blown fuse or open or short in appropriate wire.
  10. Turn ignition off. Check continuity between PCM harness connector terminal No. 4 and ECCS relay harness connector terminal No. 1 (Light Green/Red wire). See Figure & Figure . If continuity exists, go to next step. If continuity does not exist, repair open or short in Light Green/Red wire.
  11. Check ECCS relay. See RELAYS  under RELAYS & SOLENOIDS. If continuity is as specified, go to next step. If continuity is not as specified, replace ECCS relay and retest system.
  12. Turn ignition off. Disconnect PCM harness connector. Using DVOM, check continuity between ground and PCM harness connector terminals No. 10, 19, 25, 32, 116 and 124. See Figure. If continuity exists on all wires, go to next step. If continuity does not exist on any wire, repair open in appropriate wire. See WIRING DIAGRAMS article.
  13. Check PCM harness connector terminals for damage or corrosion. Repair as necessary, reconnect all connectors and retest system.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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