* Prosecutor says investigating two employees of Bosch
* Says probe relates to Grand Cherokee, Dodge Ram models
* Found signs of reduced effectiveness of emissions controls
* Bosch already probed about VW, Porsche, Mercedes vehicles (Adds background on Bosch probes tied to Porsche, VW, Daimler)
FRANKFURT, Jan 31 (Reuters) - The Stuttgart prosecutor's office on Wednesday said two employees of auto supplier Robert Bosch were being probed on suspicion of aiding fraud, as part of a wider probe into Chrysler diesel emissions in the United States.
The Chrysler Grand Cherokee 3.0 L and the Chrysler Dodge Ram 1500, which have been on sale in the U.S. since 2014, had shown signs of reduced effectiveness of emissions control systems without technical justification, the office said.
The U.S. Environmental Protection Agency (EPA) in January of last year accused Fiat Chrysler Automobiles of using hidden software to allow excessive diesel emissions to go undetected, leaving FCA facing a maximum fine of about $4.6 billion. 1/8nL1N1F212T 1/8
The Stuttgart prosecutor's office is already probing Bosch for its role in designing engine management systems for Volkswagen, Porsche and Mercedes-Benz vehicles.
In September 2015, Volkswagen admitted to using engine management systems to cheat emissions tests by using software to detect testing procedures in order to adjust filtering systems to mask higher pollution levels.
Bosch was not immediately available for comment. (Reporting by Edward Taylor; Additional reporting by Jan Schwartz; Editing by Maria Sheahan)