Common Symptoms
- Check engine light illuminated
- Rough idle or engine misfire
- Poor acceleration and reduced engine power
- Increased fuel consumption
- Engine stumbling or hesitation under load
- Hard starting or extended cranking
Most Likely Root Causes
- Faulty fuel injector on cylinder 4
- Damaged or corroded wiring harness to injector 4
- Failed fuel injector driver circuit in PCM
- Poor electrical connection at injector connector
- Shorted injector coil winding
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Component Location
Cylinder 4 fuel injector is located on the fuel rail at the fourth cylinder position, typically accessible from the engine top or side depending on engine layout.
Manufacturer Notes
Some manufacturers may require PCM reprogramming if multiple injector circuit low codes are present across different cylinders.
Also diagnosing J1939 SPN/FMI codes?
Heavy-duty trucks often throw both OBD-II and J1939 faults simultaneously. AI Diesel Tech handles both protocols in a single guided session.
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