LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Infiniti >> 2024 >> Q50 Luxe, AWD >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Engine Control System (2 Of 2) >> Symptom Diagnosis >> Engine Control System >> Engine Control System Symptoms >> Symptom Table
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Symptom Table

SYSTEM - BASIC ENGINE CONTROL SYSTEM 

  SYMPTOM Reference
HARD/NO START/RESTART (EXCP. HA) ENGINE STALL HESITATION/SURGING/FLAT SPOT SPARK KNOCK/DETONATION LACK OF POWER/POOR ACCELERATION HIGH IDLE/LOW IDLE ROUGH IDLE/HUNTING IDLING VIBRATION SLOW/NO RETURN TO IDLE OVERHEATS/WATER TEMPERATURE HIGH EXCESSIVE FUEL CONSUMPTION EXCESSIVE OIL CONSUMPTION BATTERY DEAD (UNDER CHARGE)
Warranty symptom code AA AB AC AD AE AF AG AH AJ AK AL AM HA
Fuel Low pressure fuel pump circuit 1 1 2 3 2   2 2     3   2 Refer to Component Function Check .
Fuel pressure regulator system 3 3 4 4 4 4 4 4 4   4     Refer to Work Procedure .
Fuel injector circuit 1 1 2 3 2   2 2     2     Refer to Component Function Check .
Evaporative emission system 3 3 4 4 4 4 4 4 4   4     Refer to System Description .
FRP sensor circuit 1 1 2 2 2   2 2     2     Refer to DTC Description .
High pressure fuel pump circuit     4   3                 Refer to DTC Description .
Air Positive crankcase ventilation system 3 3 4 4 4 4 4 4 4   4 1   Refer to POSITIVE CRANKCASE VENTILATION : Periodic Maintenance .
Incorrect idle speed adjustment       1 1 1 1   1     Refer to Work Procedure .
Electric throttle control actuator 1 1 2 3 3 2 2 2 2   2   2 Refer to DTC Description , Refer to DTC Description .
Ignition Incorrect ignition timing adjustment 3 3 1 1 1   1 1     1     Refer to Work Procedure .
Ignition circuit 1 1 2 2 2   2 2     2     Refer to Component Function Check .
Main power supply and ground circuit 2 2 3 3 3   3 3   2 3     Refer to Diagnosis Procedure .
Mass air flow sensor circuit 1 1 2 2 2   2 2     2     Refer to DTC Description , Refer to DTC Description .
Engine coolant temperature sensor circuit 3 3 3       Refer to DTC Description , Refer to DTC Description .
Air fuel ratio (A/F) sensor 1 circuit             Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description .
Throttle position sensor circuit     2 2       Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description .
Accelerator pedal position sensor circuit     3 2 1             Refer to DTC Description , Refer to DTC Description , Refer to DTC Description .
Heated oxygen sensor 2 circuit     6   6   6 6     5     Refer to DTC Description .
Knock sensor circuit     2               3     Refer to DTC Description .
Engine oil temperature sensor circuit     4   2           3     Refer to DTC Description , Refer to DTC Description .
Engine oil pressure sensor circuit     4   4 3 3 3     3     Refer to DTC Description .
Crankshaft position sensor circuit 2 2                       Refer to DTC Description .
Intake camshaft position sensor circuit     3   2 3               Refer to DTC Description , Refer to DTC Description .
Exhaust valve timing control position sensor circuit 2 2     3   3 3           Refer to DTC Diagnosis Procedure , Refer to DTC Diagnosis Procedure .
Turbocharger boost sensor circuit     3   3                 Refer to DTC Description .
Manifold absolute pressure sensor circuit         2                 Refer to DTC Description .
Vehicle speed signal circuit   2 3   3           3     Refer to DTC Description .
ECM 2 2 3 3 3 3 3 3 3 3 3     Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description .
Electric intake valve timing control module circuit     3   3 3               Refer to Diagnosis Procedure , Refer to DTC Diagnosis Procedure , Refer to DTC Diagnosis Procedure , Refer to DTC Diagnosis Procedure .
Electric intake valve timing control actuator circuit         3                 Refer to DTC Diagnosis Procedure , Refer to DTC Diagnosis Procedure , Refer to DTC Diagnosis Procedure , Refer to DTC Diagnosis Procedure .
Exhaust valve timing control solenoid valve circuit 2 2 2   2   2 2           Refer to DTC Description , Refer to DTC Description .
PNP signal circuit     3   3   3 3     3     Refer to DTC Description .
Refrigerant pressure sensor circuit   2       3     3   4     Refer to Component Function Check .
Electric wastegate control actuator circuit         1                 Refer to DTC Description .
Battery current sensor circuit           4 5 5         3 Refer to DTC Description , Refer to DTC Description , Refer to DTC Description , Refer to DTC Description .
Electrical load signal circuit             3             Refer to Component Function Check .
Air conditioner circuit 2 2 3 3 3 3 3 3 3   3   2 Refer to Work Flow .
ABS actuator and electric unit (control unit)     4                     Refer to Work Flow .

1 - 6: The numbers refer to the order of inspection.

(continued)

SYSTEM - ENGINE MECHANICAL and OTHER 

  SYMPTOM Reference
HARD/NO START/RESTART (EXCP. HA) ENGINE STALL HESITATION/SURGING/FLAT SPOT SPARK KNOCK/DETONATION LACK OF POWER/POOR ACCELERATION HIGH IDLE/LOW IDLE ROUGH IDLE/HUNTING IDLING VIBRATION SLOW/NO RETURN TO IDLE OVERHEATS/WATER TEMPERATURE HIGH EXCESSIVE FUEL CONSUMPTION EXCESSIVE OIL CONSUMPTION BATTERY DEAD (UNDER CHARGE)
Warranty symptom code AA AB AC AD AE AF AG AH AJ AK AL AM HA
Fuel Fuel tank 5 5                       Refer to FUEL TANK : Inspection .
Fuel piping 5 5 5 5 5 5
Vapor lock                         -
Valve deposit 5 5 5 5   5 5     5 -
Poor fuel (Heavy weight gasoline, Low octane)       -
Air Air duct   5 5   5   5 5     5     Refer to AIR CLEANER AND AIR DUCT : Inspection .
Air cleaner Refer to AIR CLEANER FILTER : Inspection .
Air leakage from air duct
(Mass air flow sensor - electric throttle control actuator)
5 5 5 5 Refer to AIR CLEANER AND AIR DUCT : Inspection .
Electric throttle control actuator Refer to CHARGE AIR COOLER : Exploded View .
Air leakage from intake manifold/Collector/Gasket Refer to INTAKE MANIFOLD COLLECTOR : Exploded View .
Cranking Battery 1 1 1   1   1 1     1   1 Refer to How To Check .
Generator circuit Refer to Work Flow .
Starter circuit 3             Refer to Work Flow .
Signal plate 6 Refer to DRIVE PLATE : Inspection .
PNP signal circuit 4 Refer to DTC Description .
Engine Cylinder head 5 5 5 5 5   5 5     5     Refer to CYLINDER HEAD : Inspection .
Cylinder head gasket 4 3  
Cylinder block 6 6 6 6 6 6 6   6 4 Refer to CYLINDER BLOCK : Inspection .
Piston
Piston ring
Connecting rod  
Bearing
Crankshaft
Valve mechanism Timing chain 5 5 5 5 5   5 5     5     Refer to TIMING CHAIN : Inspection .
Camshaft Refer to CAMSHAFT : Inspection .
Intake valve timing control Refer to System Description .
Exhaust valve timing control Refer to System Description .
Intake valve 3 Refer to CYLINDER HEAD : Inspection .
Exhaust valve
Exhaust Exhaust manifold/Tube/Muffler/Gasket 5 5 5 5 5   5 5     5     Refer to CATALYST : Exploded View , Refer to EXHAUST SYSTEM : Inspection .
Three way catalyst
Lubrication Oil pan/Oil strainer/Oil pump/Oil filter/Oil gallery 5 5 5 5 5   5 5     5     Refer to OIL PAN (LOWER) : Exploded View , Refer to OIL PAN (UPPER) : Exploded View , Refer to OIL FILTER : Inspection , Refer to OIL PUMP : Inspection .
Oil level (Low)/Filthy oil Refer to ENGINE OIL : Inspection .
Variable displacement oil pump 5 5   4             4     Refer to DTC Description .
Cooling Radiator/Hose/Radiator filler cap 5 5 5 5 5   5 5   4 5     Refer to RADIATOR : Exploded View , Refer to WATER OUTLET AND WATER PIPING : Exploded View .
Water pump Refer to WATER PUMP : Exploded View .
Water gallery Refer to System Description .
Cooling fan 5 Refer to ENGINE COOLING FAN : Exploded View .
Coolant level (Low)/Contaminated coolant Refer to ENGINE COOLANT : Inspection .
Multi-way control valve 4 Refer to DTC Description , Refer to DTC Description , Refer to DTC Description .
IVIS (INFINITI Vehicle Immobilizer System - NATS) 1 1                       Refer to Work Flow .

1 - 6: The numbers refer to the order of inspection.