Auto Service Professional

OCT 2018

Magazine for the auto service professional

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32 A S P O c t o b e r 2 018 E l e c t r i c a l S y s t e m F a i l u r e s resistance before it damages the circuit is key to saving the circuit from failing completely. Many times I've seen technicians find the cause of the failure but not repair the circuit cor- rectly. In Figure 3, you will see how excessive moisture got into this connector and caused a complete circuit failure. e cause of this was due to a misplaced seal around the terminal where it enters the connec- tor body. at little seal actually keeps moisture out of the connector body (see Figure 4). As I mentioned before, excessive resistance in a cir- cuit creates excessive heat. e key to tracking down electrical failures before they crop up is to perform preventive maintenance. As I stated in one of my previous articles, it all starts with the battery. Making sure the battery is fully charged and the connections are clean and tight is a step in the right direction. A battery ter- minal that is corroded or even loose is a point of high resistance. It's essential that those are taken care of be- fore you start your circuit troubleshooting. Once you have established a good base you can con- tinue on your diagnostic path for the circuit in question. So let's look at an electrical circuit and see how and where the trouble started. Our first vehicle in question is a 2005 Kia Sorento that was having an intermittent no-start condition. Aer retrieving the diagnostic trouble code P0336 for intermittent crank sha position signal, it was apparent that the circuit that con- trols the cranksha position sensor wasn't work- ing correctly. I performed a test on the circuit in ques- tion and found that the reading from the sensor wasn't always there. On this vehicle the cranksha sensor is locat- ed inside the front timing cover and access wasn't going to be easy. When testing of a sensor shows an intermit- tent signal, you want to be absolutely certain that you know it's either a circuit problem or a com- ponent problem. I tested this circuit from the electronic control module (ECM) as that was the easiest access point. Sure enough, I was getting a reading on my scope and then it showed a flat line while crank- ing. When I did get a signal the engine would start then stall, but in the majority of attempts it would not start. Unfortunately I had to remove the front tim- ing cover to actually get a visual of this sensor. When the covers were removed I found an ex- cessive amount of oil on the timing belt due to a leaking front cranksha seal. To remove the cranksha sensor I first had to remove the timing belt. Once the sensor was re- moved I immediately saw the problem. With the oil saturating the cranksha sensor over a pro- longed period of time it had eroded the plastic covering that protects the three wires going into the sensor assembly (see Figure 5). With the wires being exposed, moisture along with the debris from the belt created corrosion on the signal wire coming out of the sensor, which was giving me that intermittent no-start. is vehicle needed a new timing belt and cranksha seal, along with the seals that keep moisture out of the timing covers, as well as a new sensor. Besides water intrusion entering a circuit, an- other electrical circuit failure is that of excessive resistance. When a circuit has higher than normal re- sistance in a circuit it creates heat. If the heat is too high it will cause wires to melt, along with terminal ends inside of connectors to melt the Figure 4: In this instance, a faulty seal led to moisture intrusion and circuit failure.

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