Tech Tip No. 14
Originally published in the quattro quarterly
Intermittent Electrical Parts, Connectors, and Electrical
Automobiles rely on electrical connectors of one form or another to
connect switches, relays, wires, lights, electric motors, sensors, computers, and plugs together. However, generally the connectors form the weakest link in the automobile electrical system.
Automotive electrical and electronic component failures can be
traceable to connector failures.
An example is the connections to a relay. The current flow through the relay heats up the relay which in turn heats up the connector. The connector looses its grip with the relay and connector itself begins to overheat from its new resistance to current flow. It's just a matter of time before you smell something hot or burning. The plastic around the connector melting. Eventually the relay itself fails.
Connector failures are notorious for their unpredictability and
Poor electrical connections are one of the reasons why many cars run worse in the wet than they do in the dry. This unpredictability causes your Audi service department many hours of grief. Customers do not understand why a dealer cannot make a problem occur "on the bench", or fix "the problem." Technicians find it difficult to isolate the intermittent problems, and under the pressure of cost and time, resort to replacement of major components which themselves, may not be at fault. However, just plugging in the new part temporarily cleans the connector and the problem goes away until you drive it for a week or so.
Sometimes a poor connection is actually caused by a well meaning
person trying to help the problem by using cleaning sprays that contain silicones to make the connections water-repellent. Why is this harmful?
This is because silicone when certain conditions exist, can combine with metal ions to form high resistive films such as sodium silicate.
Those of you who have replaced a full throttle switch on a 200 or
5000 turbo engine know that even though the contacts are physically touching no signal gets through the switch.
This highlights that it is more difficult to design a connector to
carry a small signal than to carry large current. Contaminant films which would be of little problem for higher current flow will cause conditions in low signal current ranging from zero-crossing
distortion to an intermittent connector similar to the problems you've found with full throttle switches.
Audi is well aware of these problems and has spent a great deal of
time selecting and testing connectors.
Audi even uses gold plated contacts in critical areas! Even so, perfect connection reliability is almost impossible to obtain. An example of this is the gold plated air flow meter and throttle connections on the turbo engines with Motronic injection. I spent months trying to find a signal loss problem with our highly modified Audi. I kept getting diagnostic readings similar to "Sensor not reached limit" "Sensor limit exceeded" and "Control Unit Defective". What was the problem? Not the sensor. Not the computer. Just connector problems especially when the engine was cold, even with gold plated ones.
To Prevent Electrical Problems:
1.Avoid silicone sprays.
1.Use a good spray cleaner like DeoxIT D5 Connector &
Contact Treatment. This breaks up the oxides and contamination. This is only a cleaner and the cleaning improves conductivity.
2.Use an electrical contact enhancer like Stabilant 22 or
Stabilant 22A. Initially it is non-conductive and then switches to a conductor in the presence of electricity.
This switching ability is set so that the material will remain non-conductive between adjacent contacts in a multiple connector, and yet enhance the conductivity of each connector. It's as if it had its own brain, and it provides a tenfold to a hundredfold increase in connector reliability.
Skip this paragraph if you're not technical.
Stabilant 22 is a potentially electricly-active material which through a synergistic combination of effects enhances conductivity within a contact without causing leakage between adjacent contacts. While Stabilant 22 has a high dielectric constant it acts to form a capacitive layer which is in parallel with whatever residual resistance exists in the contact increasing the passage of AC signals. However, given sufficient DC bias within the gaps of the contact the thin film of Stabilant 22 will "switch" to conducting by quantum tunneling and thus limit the resistance of the contact to a serviceable level.
Audi has recommended that their service people use Stabilant 22,
and now I'm recommending it to Quattro Club members. It can be bought from Audi and other electronic supply sources.
Here are some uses for Stabilant 22:
The stabilant will reduce the possibility of fuse contact
heating which can cause a fuse to blow below its rated current on a circuit that is really O.K. While the new blade type fuses are more reliable than the older 3AG/AGC types they still need help.
Poor contacts in the lighting connectors will result in a
voltage drop at the connector that robs the lights of some of their brightness. Use the stabilant when replacing bulbs.
Often a "sensor malfunction" error message on a
diagnostic computer appears because of a faulty connection to the sensor. Many times you can buy a new sensor only to have the same error message re-occur hours, days or even weeks later.
The difficulty is that quite often the problem is the connector itself rather than the sensor. Replacing the sensor "cured" the problem only because the vary act of replacement simply "wiped" the connector. Using a drop on the connector may save the cost of a sensor.
Malfunctioning lights or instruments are often caused by poor
contacts. I once had an intermittent speedometer that was the result of poor connections in the instrument cluster.
Electric Side-View Mirrors
(Attention Audi 4000 owners) The tab connectors particularly
inside the doors are susceptible to contamination from some of the oil/wax rust preventative sprays, and water if you leave your door open in the rain.
Many times the contacts and the switch itself are so corroded that you would first need to use the DeoxIT D5 mentioned above.
Battery terminals, door activated switches, voltage regulators
on alternators, and plug-in relays are other areas that can be helped by use of a contact enhancer.
However, one word of caution is needed. Do not use a contact
enhancer such as Stabilant 22 on a switch for an inductive load.
In other words if the switch sparks when disconnection occurs do not use the stabilant as it would increase the sparking. (However it is O.K. to use it on the wiring harness connections for these switches and circuits.)
Were to obtain information on these items:
Craig Laboratories, Inc.
16744 West Bernardo Drive
San Diego, CA 92127-1904
FAX: (619) 451-2799
D. W. Electrochemicals Ltd.
97 Newkirk Road North, Unit 3
Richmond Hill, Ontario L4C 3G4