Technical Service Bulletins

Hybrid Misdiagnosis

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Hybrid Misdiagnosis

Some 2005-2012 Mercury Mariner hybrid vehicles may exhibit a concern where the engine stalls soon after starting. This may actually be a crank/no-start condition being misdiagnosed due to the unique characteristics of the hybrid powertrain. DTC P0A7D (battery pack state of charge low) and/or P1A0C (engine disabled) may be present.

Conventional gasoline engines use an externally mounted starter motor which can easily be heard when starting the engine. The hybrid powertrain has no external starter motor, and instead utilizes the motor/generator contained within the eCVT transaxle for this function.

The motor/generator is almost silent in operation. The higher rotational speed along with the lack of audible starter motor noise may be mistaken for the engine actually having been successfully started then stalling. A conventional externally mounted starter motor rotates the engine at 200-250 rpm when starting the engine. The hybrid eCVT motor/generator rotates the engines at 900-1,200 rpm for up to 30 seconds when starting. If the perceived stall occurs with a cold engine within 30mseconds or less after starting is initiated, the engine is most likely in a crank/no-start mode and is not a start/stall.

Inadvertently following the Powertrain Control/Emissions Diagnostic manual, section 3 symptom chart for a stall/quit at idle instead of no start/normal crank may eventually discharge the high voltage traction battery, resulting in DTC P0A7D and/or P1A0C. This may lead to the possible replacement of the high voltage traction battery.

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