Nissan/Infiniti ECU/ECM

Nissan/Infiniti ECU/ECM Post-Repair Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired Nissan/Infiniti ECU/ECM and the problem is still happening.
Important: Please do not open/disassemble the module. Opening the module can damage it and may void warranty coverage.

Common concerns this guide applies to:

• Engine power loss
• Rough idle / idle issues
• Rough start / hard start
• DTC P0505 (Idle Air Control System)
• Other drivability concerns that remain after ECU reinstall

Step 1: Confirm correct ECU and installation

• Confirm the ECU part number matches the original unit for the vehicle.
• Confirm all ECU connectors are fully seated and locked.
• Inspect for bent pins, pushed-back pins, moisture, or corrosion at the ECU connectors.

Step 2: Battery voltage and power supply check

• Verify battery voltage is healthy and the terminals are clean/tight.
• If the vehicle cranks slow, clicks, or voltage drops heavily while cranking, address battery/charging/connection issues first (low voltage can create false ECU symptoms).

Step 3: Check ECU/EFI power fuses and relays
Using the fuse cover legend, check any fuse/relay labeled:

• ECM / ECU / EFI
• IGN / ECCS / ENG CONT / INJ
• Throttle / ETCS (if equipped)
• Fuel pump (if the vehicle won’t start)
  If a fuse is blown:
• Do not keep replacing it—inspect the circuit for shorts (harness damage, sensor short, coil/injector wiring).

Step 4: Do a basic “Key ON” functional check

• Turn key to ON (engine OFF).
• Confirm the Check Engine Light illuminates (bulb check).
• Listen for fuel pump prime (if applicable).
  If the CEL does NOT illuminate:
• Suspect ECU power/ground issue, blown ECU fuse, relay issue, or wiring/connector problem.

Step 5: Scan for codes and record freeze-frame

• Scan all modules if possible (Engine + ABS + TCM).
• Record codes and freeze-frame data (RPM, coolant temp, battery voltage).
• Clear codes once, then recheck after a short run/crank attempt.
  If codes immediately return, focus on those circuits first.

Step 6: If you have P0505 / idle control issues

• Inspect and clean the throttle body (carbon buildup can cause unstable idle).
• Check for intake/vacuum leaks (cracked intake boot, loose clamps, leaking PCV hoses).
• Confirm the MAF sensor connector is tight and wiring isn’t damaged.
• If work was recently done (battery disconnected, throttle body cleaned/replaced), the vehicle may need an idle relearn procedure.

Step 7: Check for vacuum leaks and unmetered air (major cause of rough idle/power loss)

• Inspect the intake tube between MAF and throttle body for cracks/tears.
• Check brake booster hose and PCV hoses for leaks or disconnections.
• Verify the air filter housing is closed and sealed.

Step 8: Verify fuel delivery (especially for rough start / no-start / power loss)

• Confirm there is fuel in the tank (don’t rely only on the gauge).
• If possible, verify fuel pressure meets spec for the engine.
• If fuel pressure is low, suspect fuel pump, fuel filter (if equipped), regulator, or power/ground to the pump.

Step 9: Verify ignition and injector basics (rough running/misfire-like symptoms)

• Inspect ignition coils and coil connectors for oil intrusion or broken locks.
• Check spark plugs for wear/fouling and correct gap/type.
• Inspect injector connectors for loose fit, corrosion, or damaged wiring.

Step 10: If the issue is intermittent

• Wiggle-test ECU harness and connectors with the engine idling (do not force connectors).
• If symptoms change, suspect harness damage, poor pin fit, or corrosion in connectors/grounds.

Step 11: If the vehicle had recent repairs just before the issue
If the problem started right after work on:

• throttle body / MAF / intake tubing
• battery / alternator / grounds
• sensors, wiring, fuses, or relays
  …recheck those areas first. A loose connector, vacuum leak, or missed ground is a top cause of repeat symptoms after ECU reinstall.

Step 12: What to send UpFix if the issue continues

• VIN
• Exact symptoms (when it happens, hot/cold, idle only, during crank, while driving)
• All current codes (and which ones return immediately after clearing)
• Any work done recently (throttle body, battery, alternator, sensor replacement, wiring repair)
• Photos of ECU connector pins and any corrosion/damage found