Case Number: S2618000003 Rev. D
Release Date: June 2026
Symptom/Vehicle Issue: MIL-On, Engine Runs Rough
Models Affected: 2026 Jeep Grand Cherokee (WL)

Customer Complaint/Technician Observation: The customer’s complaint may
include a MIL-on condition. They may also experience a rough running engine. Upon
further inspection, the technician may find Diagnostic Trouble Codes (DTCs) for one or
more of the following issues:






P0300-Multiple Cylinder Misfire
P0301-Cylinder 1 Misfire
P0302-Cylinder 2 Misfire
P0303-Cylinder 3 Misfire
P0304-Cylinder 4 Misfire

Discussion: There are circumstances where spark plug damage can cause cylinder
misfire and subsequent engine failure. If the vehicle is exhibiting any of the symptoms
mentioned in the section above, perform the following inspection to determine the
proper diagnostic path based on the vehicle’s condition:

This document does not authorize warranty repairs. This communication documents a record of past experiences. STAR Online
does not provide any conclusions about what is wrong with the vehicle. Rather, it captures all previous cases known that appear
to be similar or related to the vehicle symptom / condition. You are the expert, and you are responsible for deciding on the
appropriate course of action.

Contact STAR Center, or your Technical Assistance Center Via TechCONNECT or eCONTACT ticket if no
solution is found
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Inspection:
 Remove the Main Chamber and Pre-Chamber Spark Plugs and mark the location
of each plug (as shown in Fig. 1) so they can be easily identified once they are
removed from the engine (use locations 1-8 as indicated in Fig. 2). Be sure to
take clear pictures of the spark plugs, they will be needed for claim
submission.

Fig. 1

Fig. 2

 Identify the condition of each spark plug:

This document does not authorize warranty repairs. This communication documents a record of past experiences. STAR Online
does not provide any conclusions about what is wrong with the vehicle. Rather, it captures all previous cases known that appear
to be similar or related to the vehicle symptom / condition. You are the expert, and you are responsible for deciding on the
appropriate course of action.

Contact STAR Center, or your Technical Assistance Center Via TechCONNECT or eCONTACT ticket if no
solution is found
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o If the spark plugs are clean, you should proceed with applicable published
diagnostic testing for cylinder misfire found in Service Library.
o If the spark plugs are fouled, replace all 8 spark plugs (see part numbers
below), but applicable diagnostic testing should be performed to ensure
there is not a root cause for the misfire different than the spark plug itself.

1

2

o If any of the spark plugs look like the plug in example 1 above, replace all 4
spark plugs of the corresponding set. For example, if a main chamber
spark plug fails, replace all 4 main chamber spark plugs (p/n-68540598AB
or latest) OR if a pre-chamber spark plug fails, replace all 4 pre-chamber
spark plugs (p/n- 68506398AA or latest).
o If any of the main chamber spark plugs look like the plug in example 2
above, replace the engine (68576058AD or latest).
o If any of the pre-chamber spark plugs look like the plug in example 2
above, block plug openings to other cylinders. For the cylinder with the
damaged spark plug, use a soft-tipped air gun to pressurize the cylinder
through the main chamber plug opening to clear any debris from the prechamber plug opening. Replace all 4 main pre-chamber spark plugs (p/n68506398AA or latest).
This document does not authorize warranty repairs. This communication documents a record of past experiences. STAR Online
does not provide any conclusions about what is wrong with the vehicle. Rather, it captures all previous cases known that appear
to be similar or related to the vehicle symptom / condition. You are the expert, and you are responsible for deciding on the
appropriate course of action.

Contact STAR Center, or your Technical Assistance Center Via TechCONNECT or eCONTACT ticket if no
solution is found
Stellantis US LLC

Version 4.5 06/08/2022

If spark plug replacement is performed, please top-off the fuel tank using premium
fuel before returning the vehicle to the customer. If the engine is replaced, please
drain the fuel tank using the applicable procedure found in Service Library (09 Engine, 2.0L / Fuel System / Standard Procedure / DRAINING FUEL TANK). Leave
enough fuel (as required) in the fuel tank to drive the vehicle to a fueling station.
Take the vehicle to a fueling station and fill it with premium fuel before returning the
vehicle back to the customer. For more information regarding the fuel fill process,
please see Warranty Bulletin D-26-13 for spark plug replacement repairs and D-26-14
for engine replacement repairs.
If any of the above conditions do not apply to the vehicle but possible misfire
symptoms still exist, please follow published diagnostic routines found in Service
Library.
At this time, service replacement engines for this application are on parts restriction
and must be ordered through the STAR Center. Please contact STAR as soon as
possible to support expedited parts procurement for repairs.
Engineering is currently investigating conditions under which spark plug damage may
occur. Additional updates and recommended actions will be provided as they become
available.
In the interim, please ensure affected customers are supported through the Courtesy
Transportation Program.

This document does not authorize warranty repairs. This communication documents a record of past experiences. STAR Online
does not provide any conclusions about what is wrong with the vehicle. Rather, it captures all previous cases known that appear
to be similar or related to the vehicle symptom / condition. You are the expert, and you are responsible for deciding on the
appropriate course of action.

Contact STAR Center, or your Technical Assistance Center Via TechCONNECT or eCONTACT ticket if no
solution is found
Stellantis US LLC

Version 4.5 06/08/2022