There are some complaints and issues with the 12 volt battery being low voltage intermittently causing this issue here needing replaced.it may have checked/tested o.k. for them when they had the vehicle but this can cause this fault here.The throttle body is the main cause though and several complaints on this causing this fault here.It might be worth replacing since they cannot locate the fault and having the 12 volt battery and battery cables and connections checked.Below is the operating characteristics that are normal for this engine and if there are abnormal operations occuring that do not fit this below then I would check into the battery,cables and throttle body as one of these will be the cause here.
• Stall during shift out of park immediately following engine crank. This is a normal operating characteristic. Some drivers are able to interrupt the engine start sequence by shifting the transmission out of park. The ECM will turn off fuel and spark to the engine if it isn’t running and the transmission has been shifted out of park or neutral. Inform the customer to wait one to two seconds before shifting out of park or neutral to ensure that the engine is running and has completed the start sequence.
• Engine restarts in reverse from Auto Stop. This is a normal operating characteristic as the engine will restart any time the gear selector is in reverse. When reverse remains in electric mode, however, the engine restarts to provide an audible indication to pedestrians.
• Slight bump in driveline during acceleration. This is due to transition from V4 to V8 and vice versa. In Mode 2, the engine is able to operate longer in four-cylinder mode under light throttle for improved highway fuel economy. As more power is needed, the system will transition to V8 Mode. This is a normal operating characteristic of a hybrid powertrain to maximize fuel economy.
• Low pitch noise during Auto Stop. This is a normal characteristic operation of electric coolant pump or hybrid battery fan. During Auto Stop, the engine isn’t running and the interior cabin is quiet. These pumps run to keep the electronics from overheating, even in cold ambient temperatures. This noise may be more evident during high ambient interior temperatures. Advise the customer to keep the battery vents clear and not to carry cargo in the second row footwell area. The electric coolant pump runs in Auto Stop to circulate coolant to the HVAC system to maintain cabin temperature. That pump (under the right conditions) will run and may be barely audible.
• 12-volt operation. In order to maintain peak capacity in the 12-volt system, it’s recommended that customers allow the vehicle to remain in “run” when parked and attended. When the ignition switch has been turned to crank and is set to “run,” the engine will run until the desired state of charge in the 300V battery has been reached. At that point, the vehicle will enter auto-stop mode, and the Accessory Power Module (APM) will continue to power the 12-volt system. Failing to allow the APM to power the 12-volt system could cause discharge of the 12-volt battery. Examples of activities that may cause stress on the 12-volt battery include: tailgate celebrations, usage of the rear seat entertainment system with the vehicle off or listening to the radio for extended periods of time with the vehicle off. In these situations, the recommended operating mode is to start the engine. Normally, the vehicle will enter Auto Stop mode and, as the 12-volt battery needs charging, the system will automatically start the engine to keep the system fully charged. In addition to allowing the APM to power the vehicle’s 12-volt system, special care should be taken when storing this vehicle. If the vehicle is to be stored for more than 20 days, the 12-volt battery should be disconnected. If the vehicle is to be stored for more than 60 days, the 12-volt battery should be charged to capacity no less than once every 20 days.
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