Diagnostic trouble code (DTC) information

Condition 

Diagnostic trouble code (DTC) ECM-3503 is stored if the control module registers that the engine is misfiring to such an extent that there is a danger of damage to the three-way catalytic converter (TWC) (the extent varies with load and engine speed (RPM)).

ECM-3503 is always stored together with a diagnostic trouble code (DTC) which indicates the cylinder which is misfiring (ECM-35X3).

Substitute Value 

• three-way catalytic converter (TWC) diagnosis shut off
• leakage diagnosis shut off
• rear heated oxygen sensor control shut off.

Possible Source 

• fuel stoppage
• repeated cold starting where the engine coolant temperature (ECT) has not reached normal operating temperature between starts.
• water in spark plug wells
• defective spark plugs
• contaminated or faulty fuel
• air leakage
• Blocked crankcase ventilation.
• Damaged VVT-unit.
• blocked / leaking injectors
• faulty fuel pressure
• uneven compression

Fault symptom[s] 

• engine misfires
• engine difficult to start
• poor performance
• uneven idle
• the engine does not run on all cylinders.