Fretting
corrosion is a buildup of insulating oxidized debris (nonconductive material)
caused by micro motion between two contact surfaces.
It's
commonly found on tin plated terminals, such as Micro pack 100 and Micro pack
64 connections.
Past
Serviceability Issues
Replacement
of sensors, modules and other components will result in only a temporary relief
of a fretting issue. Actually, just the cycling of a connector will clear the
fretting corrosion from the terminal, correcting the condition for a short time
until fretting corrosion builds back up again.
Typical
issues caused by fretting corrosion include:
·
Intermittent electrical
component operations
·
DTCs being set, or No
Trouble Found (NTF)
·
Low current signal
circuits -- fretting corrosion (high resistance) can cause intermittent
connections
·
High current power
circuits -- permanent increases in the connection resistance can lead to
overheating
Evidence
of Fretting
Fretting
usually appears as small, dark smudges on electrical terminals or smudges at
the locations of electrical contact. In less severe cases, it may require a
magnifying glass to identify a fretting condition. (Fig.
5)
Causes
of Fretting
Fretting
is caused by the motion between the connector and the terminal, which can be
due to:
·
Vibration - micro motion
between two contact surfaces causing build up of insulating oxidized debris
(nonconductive material)
·
Thermal cycling
·
Packaging of the
connector, wiring harness and/or device
·
Poor connection/terminal
retention
Fretting
corrosion may begin when a connection is made through the cracks in the
tin-oxide layer, making a stable connection. When the terminal vibrates or
moves, a section of the clean tin is exposed to the air and it quickly forms an
insulating tin-oxide film.
Every
time there is motion at the contact spot, the cycle repeats -- more tin oxide is
worn away and debris builds up. With continued microscopic fretting, enough
insulating tin-oxide wear debris can build up high resistance, creating
intermittent connections.
Service
Solution
Disconnecting
and reconnecting a connector will temporarily "fix" a fretting
condition, but it will eventually come back if the conditions for fretting
still exist. The best preventative measure is to perform the following:
1.
Disconnect the
appropriate module(s)/connector(s)
2.
Lube both sides of the
connector (module side and harness side) with NyoGel® 760G lubricant,
GM part number 12377900 (Fig. 6)
3.
Reconnect the connector
4.
Wipe away any excess
lubricant
5.
Duplicate the condition
per the appropriate Service Information
If
the condition CANNOT be duplicated, the repair is complete. Do not replace the
module/component/part.
If
the condition CAN be duplicated, the repair is incomplete. Check the
appropriate Service Information for additional diagnostic procedures.
-
Thanks to Rob Prough, Keith Borowy and Pamma Chana
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