Auto Service Professional

JUN 2018

Magazine for the auto service professional

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12 A S P J u n e 2 018 e battery current sensor monitors the bat- tery current. It directly inputs to the BCM. It creates a 5 volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100%. Normal duty cycle is between 5-95%. Between 0–5% and 95–100% are for diagnostic purposes. Once you have determined that the battery is operating as designed, then the next step in the diagnostic process involves the charging system. e charging system of the vehicle is just as im- portant as the battery itself as this is the part of the electrical system that keeps the battery in check. e charging system helps maintain the bat- tery state of charge by regulating how, when and for how long the battery needs to be replen- ished. When beginning your charging system diagnosis, the very first thing you should do is to perform a good visual inspection. Perform- ing a good visual inspection might alert you of a potential problem, thus minimizing the risk of a misstep in your diagnosis. One thing to look at is the belt that allows the alternator or generator to spin. Is the belt cracked, frayed or loose? In what condition is the pulley or pulleys that the belt rides on? Don't for- get about the tensioner and pulley. Is it in good working condition? Look for any signs of oil or coolant on the belt which could allow the belt to slip on the pulleys and possibly deteriorate the belt and shorten its life span. Another area to check would be the electrical connections to the alternator. Give the connec- tions a tug to see if they could be loose. If the con- nection is loose, it's not going to operate properly. In order to determine if the alternator or gen- erator is electrically charging correctly, you need to know what the specs are for the vehicle you are working on. ese can be obtained through the vehicle manufacturer or a service informa- tion system. On our demonstration vehicle, the 2017 Chevrolet Cruze, the charging system is moni- tored and controlled by the vehicle's ECM. e engine control module (ECM) uses the generator turn ON control circuit to control the load of the generator on the engine. A high side driver in the ECM applies a duty cycled voltage to the voltage regulator. e duty cycle controls the voltage regulator to turn the field circuit ON and OFF. e ECM monitors the state of the generator turn ON con- trol circuit. e ECM should detect low voltage on the generator turn-on control circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the en- gine running, the ECM should detect high volt- age when the duty cycle voltage is commanded high, and a low voltage when the duty cycle volt- age is commanded low on the generator turn-on control circuit. C h a r g i n g S y s t e m s The 2017 and 2018 Chevy Cruze battery is located in the trunk, with access via the trunk or by removing the rear seat. Battery power jump/inspection terminals are located at the rear of the fuse junction block.

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