SPN 655 - FMI 5 (Fault Code 323)

Injector Solenoid Driver Cylinder 5 Circuit - Current Below Normal or Open Circuit

Injector Circuit

Fault Code: 323
PID(P), SID(S): S005
SPN: 655
FMI: 5
Lamp: Amber

REASON: Injector Solenoid Driver Cylinder 5 Circuit - Current Below Normal or Open Circuit. High resistance or no current detected at number 5 injector driver or RETURN pin.

EFFECT: Engine can misfire or possibly run rough.

Circuit Description:
The injector solenoid valves control fueling quantity and injection timing. The engine control module (ECM) energizes the solenoid by closing a high-side and a low-side switch. There are two high-side switches and six low-side switches inside the ECM. The injectors for cylinders 1, 2, and 3 (front bank) share a single high-side switch that connects the injector circuit to the source of high voltage inside the ECM. Likewise, the injectors for cylinders 4, 5, and 6 (rear bank) also share a single high-side switch. Each injector circuit has a dedicated low-side switch that completes the circuit path to ground inside the ECM.

Component Location:
The engine harness connects the ECM to three injector circuit pass-through connectors that are located in the rocker housing. Internal injector harnesses are located under the valve cover and connect the injectors to the engine harness at the pass-through connectors. Each pass-through connector provides power and return to two injectors.

Shop Talk:
• Fault activation: The ECM senses current as each injector is actuated. If the ECM detects a persistent circuit error on an injector circuit, this fault will become active. If a circuit error is determined to cause excessive current, the ECM will disable the injection event for the faulty cylinders.
• Fault deactivation: The ECM will attempt to enable any disabled injector circuit whenever the engine is started and approximately once per minute while the engine is running. If an injector circuit fault is active and the faulty condition is repaired, the fault will become inactive once the engine is restarted or if the engine is permitted to idle for more than a minute.
• If a fault condition is intermittent and especially if more than one injector fault code is in the ECM memory, look for a wire harness that can short to components inside the rocker housing or a short to ground in the injector solenoid.
• If more than one injector fault code is occurring and the faults occur for injector circuits in the same bank, a short circuit exists.
• If the faults occur intermittently or faults occur, the engine can exhibit a misfire even if the injector circuit fault code does not always register. If a single cylinder exhibits misfires, look for an open circuit problem. If several cylinders on the same bank exhibit misfires, look for a short circuit anywhere in the bank of cylinders.

Causes of a single injector fault are:
• Open circuit in the engine harness(es) or injector solenoid
• High resistance in a single injector or injector solenoid
• Extremely low resistance in an injector solenoid (injector shorted internally but not to ground)
• Damaged ECM
• An intermittent short.
An intermittent short can result if the wiring harness insulation rubs through near a rocker lever. An intermittent short can cause a single injector fault code. For example, a short on the harness to cylinder number 1 causes a fault code for cylinder number 2 or cylinder number 3.

Causes of multiple injector fault codes in the same bank of injectors are:
• Short circuit in the engine harness(es) - either shorts to ground or to other wires in the engine harness
• Short circuit in any of the three injectors in the bank - shorts to ground
• Damaged ECM.
When looking for short circuits in the injector harnesses, pay particular attention to the wire insulation. Make sure there are no shorts to a rocker lever.
Note: Fault Code 951 (cylinder balance) can also be present due to this fault code.

Read More:
SPN 251 - FMI 2 (Fault Code 319)
SPN 651 - FMI 5 (Fault Code 322)


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