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VW Golf's Problems Point Up That One Should Never AssumePosted 10/8/2001By David Tidaback
We've all heard the old saying, “never assume,” but it bears periodic repeating. Don't assume that just because a problem normally has a certain cause, it will have the same cause next time it turns up. Experience is a great teacher, but it can sometimes make us overlook things we might think to check if we were less experienced. A case in point: I recently took a hotline call from a technician working on a late-model Volkswagen Golf with the “Check Engine” light on and a horrible rotten egg reek. He did not know how to test for fault codes on this particular car, but because of the light and the smell, he assumed there was a fuel mixture problem. I faxed him information on extracting codes from the engine management system and advised him to test O2 sensor output since his shop did not have an exhaust gas analyzer. He called back with the results of his testing - the fault code that had been turning on the “Check Engine” light was for the camshaft position sensor, but the O2 sensor was dead, reading 0.2v all the time. I gave him tests to conduct for the cam position sensor and advised him to replace the O2 sensor, since the car was well past its usual change interval. When the technician called back, he told me he had taken care of the cam position sensor code by indexing the sensor. It had been a little out of phase with the crank sensor, probably because of timing belt stretch. He also had replaced the O2 sensor, and now it was switching absolutely normally, but while driving the car, he could still intermittently smell a strong rotten egg odor. By this time, I was considering a bad catalytic converter, but wanted to confirm a rich mixture. I had him monitor the O2 sensor voltage while driving on the street and it still showed perfectly normal switching. An additional bit of information was that the car would not always smell - almost never at idle or while driving at low speeds - and only part of the time during or immediately after a drive at higher speed. He said he'd give it another test drive and watch the O2 sensor voltage more carefully. The tech called the next day to tell me that when he drove the car the night before, he had seen the headlights brighten and then had smelled rotten eggs again. He checked the output of the alternator, and at high engine speeds it was intermittently putting out as much as 19 volts. This time the rotten egg smell was caused by an overcharging battery and a new alternator solved the problem. Had we assumed the fuel mixture problem or a bad catalytic converter was the cause of the rotten egg smell, we might not have tested other options.
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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