Nissan/Infiniti ECU

Nissan/Infiniti ECU Higher Price Post-Repair Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired Nissan/Infiniti ECU/ECM (Higher Price group) and the problem is still happening.

Important: Please do not open/disassemble the module. This can damage the unit and may void warranty coverage.

Step 1: Confirm correct ECU + install

• Confirm the ECU part number matches the original
• Make sure ECU connectors are fully seated and locked
• Inspect for bent pins, pushed-out terminals, corrosion, water/oil intrusion, or damaged connector seals

Step 2: Battery + power integrity

• Fully charge the battery (low voltage can trigger comm faults/no-start)
• Clean/tighten battery terminals
• Verify engine/chassis grounds are clean and tight (especially near engine block and body ground straps)

Step 3: Verify ECU power feeds and fuses (test, don’t eyeball)

• Check all ECM/IGN/EFI fuses with a test light or meter
• Verify ECM relay and IGN relay operation (swap with a known-good relay if possible)
• If equipped, check fusible links for opens/high resistance

Step 4: No communication with ECU/ECM

• Confirm the scan tool powers up and can access other modules
• If no modules communicate: suspect OBD power/ground fuse or network power issue
• If other modules communicate but ECU does not:
  • Re-check ECU power/ground at the harness
  • Inspect CAN wiring near ECU for rub-through or aftermarket splices

Step 5: DTC communication codes (U-codes)

• Clear codes and cycle key OFF/ON, then re-scan
• If communication codes return:
  • Inspect battery voltage during crank (voltage drop can cause U-codes)
  • Check for loose grounds, blown IGN/ECM fuses, or failing ECM relay
  • Look for aftermarket devices (remote start, alarm, audio) tied into CAN lines

Step 6: No-start condition

• Verify immobilizer/security indicator behavior (security faults can cause crank/no-start)
• Confirm fuel pressure meets spec for the vehicle
• Check for spark and injector pulse during crank
• If spark and injector pulse are missing, focus on crank/cam sensor signals and their wiring

Step 7: Fuel injector issues

• Verify injector power feed (injectors often share a fuse/relay-fed power source)
• Inspect injector harness for cracked insulation, oil saturation, or stretched wiring near the rail
• If one cylinder issue persists, swap injector positions (if applicable) to see if the fault follows the injector

Step 8: If the issue started after recent work

• Re-check anything recently touched: battery/grounds, fuse boxes, relays, intake/MAF connections, sensor plugs
• Look for pinched harnesses, unplugged grounds, or blown fuses caused during the repair work

If the issue is still present

• Have ready: VIN, ECU part number, exact codes (especially U-codes), and symptom details (no-comm / no-start / injector issue).
• If the problem happens immediately after install and you need fast help, call or email UpFix for quicker support.