Euro Comfort Control System Can Become Tech's 'Headache'
By Jim Newkirk
What happens when the electronic comfort control (CC) systems that make life so easy for the driver become "headache control" systems for the technicians who troubleshoot and repair them? Kind of makes you long for that old manual window crank, doesn't it?
Let's start up the "way-back-when" machine and fondly remember a time when window and door locks were manually operated and almost completely trouble-free. Now fast forward across the years when all aspects of vehicle operations are controlled electronically ... just push a button and a window rolls down, flip a switch and all the doors lock ... you can even open the trunk without leaving the driver's seat! Now that's comfort! Or is it? What happens when the electronic comfort control (CC) systems that make life so easy for the driver become "headache control" systems for the technicians who troubleshoot and repair them? Kind of makes you long for that old manual window crank, doesn't it?
The CC system on the Volkswagen Passat is used for starting the engine, window and sunroof control, door locks, interior lighting, and mirrors ... the list just keeps growing! This particular 1999 Passat came into the shop with the following symptoms: No crank/no start, windows have stopped working, and the battery goes dead after sitting for a day. This should be straightforward - a quick scan for trouble codes in the affected systems should narrow the problem quickly.
But wait - the scan tool won't communicate with the power train control module! As a matter of fact, the scan tool won't communicate with any processor on the car! So where do you start to diagnose a problem like this without any scan tool access? Take a look back at everything the CC system helps control. It should be obvious that a fault in the CC system could potentially cause some, if not all, of the reported symptoms on this vehicle.
- Start by locating the CC module on this Passat so that electrical checks can be performed. A quick look at the service manual confirms that the CC module is located under the carpet, driver's side, below the front seat. Think about this component placement for a moment ... a sensitive electronic component and its related wiring is placed at the lowest part of the vehicle interior, below carpeting.
This area can catch all the snow and salt and water kicked off shoes as people enter the vehicle, and all of this snow and salt and water is sitting on a piece of carpet above the CC module and wiring. If you recall good old Sir Isaac Newton's encounter with an apple, you will quickly realize that gravity is not going to be your friend in this scenario. What you have is a perfect recipe for strange behavior from the CC module. Pulling back the soggy carpet reveals a small lake partially submerging the CC module. Odds are that the CC module has already been damaged beyond hope of salvation.
- Disconnect the module. Check to see if scan tool communication has been restored to other systems on the vehicle, and if the battery draw has been eliminated. Note: on a Volkswagen, a maximum of 50 milliamps battery draw after 30 minutes is a normal condition. Battery draw in the 200- to 300-milliamp range is usually associated with a controller that has not entered sleep mode.
- If the scan tool can now access other systems, and the draw is back to the normal range, replace the CC module.
- But don't stop here. You will notice the main wiring harness running from the CC module under the driver's carpet and heading toward the front of the vehicle. This wiring is carefully wrapped for protection from everything other than standing water! Be sure to open the harness completely and inspect all wiring and connections within for corrosion or damage. Once the wiring has been dried and repaired, check for water staining at the base of the driver's "A" pillar. Vehicles equipped with sunroofs route the sunroof drain down the interior of the "A" pillar and dump the water overboard into the wheel well. If this drain comes loose, all that drain water dumps right back on top of the CC module and wiring harness.
- Once the wiring is repaired and the module replaced, it is necessary to reprogram the system to restore normal operation. A full function factory compatible scan tool is required to reprogram the CC module for correct vehicle equipment and function.
Once this beast is under control and everything works normally, remind the customer not to leave large amounts of snow melting on the floor and to close the sunroof if it looks like rain. A little care on the customer's part can help minimize the buildup of water and a repeat performance. Armed with knowledge and good old common sense, even "headache control" systems can be effectively diagnosed and repaired.
Jim Newkirk is the Identifix European team leader. He is an ASE master with L1 and Bosch BSC certifications.
This information is provided by IDENTIFIX®. IDENTIFIX® resources cut diagnostic time and provide repair solutions that increase the shop's bottom line. From Repair-Trac pattern failure quick fixes, to Diagram-Online wiring diagrams by fax, to the Repair Hotline staffed by 32 master techs who specialize in diagnosing complex problems by phone or fax, IDENTIFIX® helps techicians fix more cars in less time.
For more information on IDENTIFIX, call (800) 288-6210, 8 a.m. - 6 p.m. Central Time.
© 2011 IDENTIFIX. All Rights Reserved.
© 2006 IDENTIFIX. All Rights Reserved.
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