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SPN 656 - FMI 5 (Fault Code 325)

SPN 656 - FMI 5 (Fault Code: 325)
SPN656 FMI5
ISB - Injector Circuit

CODES:
Fault Code: 325
PID(P), SID(S): S006
SPN: 656
FMI: 5
Lamp: AMBER
SRT:
ISC and ISL - Injector Circuit

REASON:
Injector Solenoid Driver Cylinder 6 Circuit - Current Below Normal or Open Circuit. High resistance or NO current detected at cylinder 6 injector supply or return pin.



EFFECT: Engine can misfire or possibly run rough.

Circuit Description:
The injector solenoid valves control fueling quantity and injection timing. The electronic 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 housing pass-through connector provides power and return for two injectors.

Conditions for Running the Diagnostics:
This diagnostic runs continuously when the engine is running.

Conditions for Setting the Fault Codes:
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 cylinder(s) that are faulty.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The injector will be disabled for the faulty cylinder.

Conditions for Clearing the Fault Code:
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 1 minute.

Shop Talk:
Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

• 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 cylinder(s) that are faulty.
• 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 1 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 circuit 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 fault(s) occur intermittently, 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.

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 circuit to ground in the injector solenoid.

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.


Same Bank Fault Codes:
• Bank 1 - Front Bank: Fault Codes 322, 324, 331
SPN 651 - FMI 5 (Fault Code 322)
SPN 653 - FMI 5 (Fault Code 324)
SPN 652 - FMI 5 (Fault Code 331)
• Bank 2 - Rear Bank: Fault Codes 323, 325, 332.
SPN 655 - FMI 5 (Fault Code 323)
SPN 656 - FMI 5 (Fault Code 325)
SPN 654 - FMI 5 (Fault Code 332)










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