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Last updateWed, 06 Dec 2017 2pm

On The Road

Coming through in the clutch after a bad start

I have experienced so many different automotive failures that you would think I have seen them all. However, what I saw last month made me feel like cars really are just out to get me sometimes.

On a recent Monday morning, a new customer dropped off his 2003 Volkswagen Passat sedan (manual transmission) for a 160,000-mile service and check-engine light. Whenever we are checking in a new customer and car, we have to get all relevant information. I walked out to the car with the customer to get the vehicle identification number, production date and mileage. Then I started the car to see if there were any warning lights on in the dash. That’s when I got a surprise.

Before I detail the problem, let me explain start safety systems. Both manual and automatic cars have a start safety system built in. A manual transmission car has a neutral safety switch that is part of the clutch pedal. This switch tells the ignition system if the clutch pedal is depressed or not. If the clutch pedal is not depressed, the ignition switch cannot command the starter to turn on. The reasoning behind this is so that a car cannot start in gear. For example, if you were to leave the car in first or second gear after turning it off, the car would not lurch forward on startup if the clutch pedal is depressed.

The principal is similar on an automatic system, yet there are three components involved. There is a brake pedal switch (identical to the clutch switch) that tells the start system that the brake is depressed and also releases a solenoid (electromagnetic coil) that locks the shifter in the park position. There is also a switch built into the transmission selector switch, called the neutral safety switch. A car with an automatic transmission will not start until it knows that the brake is depressed and the car is shifted into park or neutral.

Diagnosing the problem

Back to the Passat. I had the clutch and brake pedal depressed and started the car. It started, but I heard a terrible grinding sound. I figured out that if I released the clutch pedal, the noise went away, but if I depressed the clutch pedal, the noise came back. So I asked the customer if the car had made that noise before. He shook his head and looked at me like I had destroyed his car. Because I had never seen or heard of such a problem before, I instantly went into diagnostic mode.

I cycled the ignition switch and the noise was gone when I started it the second time. The first thing I thought was that possibly there was a problem with the clutch throwout bearing, as the noise occurred when the clutch was depressed all the way. Yet that was unlikely, because the customer had never heard the noise and it went away on the second startup.

As the customer and I were walking back to the office, the solution hit me. Volkswagen ignition switches are made of plastic and commonly break. Once they break, they become unpredictable. They can make lights turn off and on, make cars shut down and lose power – and even keep the starter motor running.

In the end, the culprit was the ignition switch. The ignition was intermittently broken in the start position, so even after the car was turned on, it was still giving the start command. But the starter would not engage until it saw the signal from the clutch switch. When I was pushing the clutch pedal while the car was running, the starter kept turning on and hitting the flywheel.

This was just another example of how cars are complex machines. They may not be out to get me, but they certainly keep me on my toes.

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