Enhancing the working distance of the Electronic Key Fob

If your 993 remote keyless entry fob seems to only work from a very short distance even after refreshing its battery the distance can potentially be dramatically improved by replacing some inexpensive failed components. The components are in the immobilizer controller under the driver's seat on US delivered cars. 

It turns out this is simply the result of two capacitors drying out from age that affect the radio receiver in the controller under the driver's seat. If one is handy with electronics replacing the two capacitors is not too difficult. In fact, the hardest part of the job is removing the seat and the shroud covering the controller under the seat.

Here are the steps to gain access to the Immobilizer/Fob receiver and the DME controller:

• Disconnected the car's battery before starting the procedure.
• Remove the driver's seat on left-hand drive cars, here is how to do it with a minimum of drama.
• Drill out the security rivets on the cover over the controllers under the driver's seat.
• Use a shop vacuum to clean out the metal shards left from drilling before unplugging the controller to avoid contaminating the electrical connections.
• Replace the cover when finished with some self-tapping machine screws as it may be providing some required electrical shielding.

Here are the following steps to repair the Immobilizer/Fob controller:

• Detach, unplug and remove the black plastic controller box next to the metal larger Bosch DME ignition controller.
• Open the controller's housing and locate the two electrolytic capacitors that look like small metal cans wrapped in plastic shrink wrap on the circuit board.

They are labled as follwed:

• 330uF/10V,  In plain English,  330 Micofarad, 10 Volt electrolytic capacitor

and a

• 0.47uF/50V capacitor

Replacement capacitors can be purchased on eBay or at any electronics supply house, for example:

•  Allied Electronics & Automation

Be sure to pick ones with similar housings to the originals ones to facilitate the reinstallation.

 

• Note the polarity of the old capacitors by their markings on their case when removing them, see below, and install the new ones, putting the new ones in so the wires on it marked (+) and or  (-) are put in the same mounting holes as the original ones. Usually, only one wire lead is marked.

Removing and replacing the capacitors is relatively easy if you are handy with a soldering iron however the circuit board is a two-layer board with wire traces on the front and back so 

• Be sure to unsolder the capacitor leads to both the front and back of the board as needed. 
• Be sure to use led-based rosin core solder NOT the newer lead-free alloys that require heating to higher temperatures and 
• Use a low-watt pencil-style soldering iron, 35-watt max. 
• Use care not to overheat the board and solder the replacement capacitors to both the front and the back sides of the circuit board's mounting holes. 
• The traces are very close, so use a magnifier to check that the solder joints are good and you didn't inadvertently jump and join an adjacent wire trace.

• Once the new capacitors are installed button things back up, reattach the battery, and you are done!

Updating the capacitors has resulted in my fob working from as far away as I can get from the car in my drive, where previously on a good day it would only work from five or six feet.

Who would think?

Andy

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