PIC6378B

Bulletin No.: PIC6378B
Published date: 03/3/2022
Preliminary Information
PIC6378B Diagnosing Various Concerns On A Power Folding Top
Models
Brand:
Model:
Model Years:
VIN:
from
Engine:
to
Transmissions:
Buick
Cascada
2016 - 2019
All
All
All
All
Cadillac
XLR
2004 - 2009
All
All
All
All
Chevrolet
Camaro
2016 - 2022
All
All
All
All
Chevrolet
Corvette
2005 - 2022
All
All
All
All
Pontiac
G6
2006 - 2010
All
All
All
All
Involved
Region or North America
Country
Additional
Power Folding Top
RPO
Some technicians may have to service a power folding top on one of the vehicles listed above. The
concern may be any number of issues related to, but not limited to, the folding top being completely
inoperative, the folding top only moves in one direction, or the folding top only partially completes a
Condition
cycle. Any number of folding top-related DIC messages may be accompanied with the customer's
concern as well. This PIC will provide a general overview / direction on how to begin diagnosing a
concern related to the various power folding tops used on GM vehicles.
Concern As with all customer concerns, the rst step in diagnosing a folding top issue is to fully understand the
customer's description of the concern. In many instances, what the customer describes is not exactly
what is found by the technician when he or she inspects the vehicle. Understanding what happened,
or what the customer did, right before the concern began, is crucial to correctly diagnosing the folding
top.
Once the concern or the symptom is understood, the next step is operating the folding top to
determine what works, and where does the top stop moving during its cycle. Just because the top
operates in one direction, or some functions of the top will work, this does not necessarily mean that
the top will operate correctly in the opposite direction. For example, on the Cadillac XLR, the deck lid
opens as part of the normal folding top opening cycle. In many cases, the rear compartment will open
and close correctly all by itself, but it will not operate at all when the folding top is cycled.
An important step often overlooked by many technicians in the eld is to look for any folding top
related messages in the DIC during operation. In many cases, there will be a "Top Not Secure" or a
"Only Manual Operation of Top Possible" message displayed. With a "Top Not Secured" message for
instance, this indicates that the top is somewhere in the middle of the cycle. It only indicates that the
top is not fully closed, nor is it fully open. It simply indicates that it is somewhere in between. By itself,
this is not an indication of a fault with the folding top system.
The next step in diagnosing a power folding top concern is to check for any DTCs that may have set and
follow the applicable owchart in Service Information.
If no codes are found, the next step that must be completed is to follow the applicable folding top
sensor matrix. This is essentially a chart of all the various switches and sensors in the folding top
system. It tells the technician what each one SHOULD be reading, based on where the top is at in
its cycle. With all folding top systems, the top opening or top closing cycle is broken down into a series
of small steps, called phases. There can be any number of phases in a complete folding top cycle. A
folding top must always complete the rst phase before it continues on to the second phase. The
folding top must complete the second phase before it continues on to the third phase, and so on. In
most cases, the folding top will stop partway through its opening or closing cycle with no DTCs set.
This is the most common type of customer concern. This is almost always the result of a sensor or
switch that is simply not transitioning its status. If no wiring concern is present, then no DTC will be
set, generally speaking. The matrix is used at that point to determine which switch or sensor is not
transitioning correctly, and therefore, will require a closer inspection.
The matrix for each vehicle can be found in SI. It may be located in Description and Operation, or it
may be located in a separate bulletin / PIC. Regardless, this chart is essential to diagnosing a concern
within the folding top system.
Note: A full folding top matrix is not listed for the C8 generation Corvette (2020+ model years). This is
a fully electric folding top and the matrix only lists the parameters as they should read in the fully
closed, and the fully open positions. The reason the matrix does not match the full phases of the other
vehicles, is that the C8 Corvette folding top is capable of setting DTCs when a particular sensor does
not transition. The servicing technician will automatically have a direction to head in if the top stops
working based on the DTC that sets.
The top must then be operated until the point where it stops moving. Only press and hold the folding
top switch one time. Once the top stops moving, do not keep pressing the top switch to try and get the
folding top to keep moving. Release the switch and use the scan tool to monitor each one of the
folding top position sensors / switches. Run down the matrix to see what each sensor should read,
and compare this to the scan tool information for what each sensor is actually reading. At least one
parameter should be incorrect. This is the switch or sensor that will require closer inspection. If only
one parameter is incorrect, this area will need to be further diagnosed. The tech will need to rst
determine if this is a mechanical issue or if it is electrical. Determine if the linkage is bent or did the
sensor move out of position? Is the sensor's corresponding magnet missing, or was a wiring fault
found? Is the panel simply misaligned? This will at least narrow the concern down to one speci c
area.
Example Case: Let's take a 2018 Chevrolet Camaro for instance, with a basic folding top concern. The
customer states that the top will open ne, but it will not close all the way. A preliminary check will
indicate that there is a "Top Not Secure" message in the DIC, but no DTCs are set. The tech is able to
duplicate the concern each and every time. When closing, the top will lift up out of the stowage
compartment, latch tightly to the windshield header, and the tension bow will lift up to a 45° angle.
The Rear Stowage Compartment Lid will lower and lock into position, but the tension bow will not
lower. It simply remains suspended in the air as seen in the photo below. The folding top pump quits
working and the top stops moving at that point.
On a correctly working car, the stowage compartment lid must close completely before the tension
bow is commanded down. Because the steps or phases must be completed in order, the technician
must go to the point where the failure occurs, and then go back one step to look at the scan tool data.
If we look at the Folding Top matrix found in SI, we have the following parameters seen below. This
particular vehicle has two separate Stowage Compartment Lid Closed Position Sensors. One is on the
left hand linkage and the other is on the right hand linkage. On a working vehicle, both Stowage
Compartment Lid Closed Position Sensors should read "On" when the lid is closed.
Looking at the scan tool sensor data below, we can see that only one of the two Stowage Compartment
Lid Closed Position Sensors read "On". Because the Folding Top Control Module will not command the
tension bow to lower if both Stowage Compartment Lid Closed Position Sensors are not showing that
they are closed, the module thinks that the stowage lid is still raised. As a matter of operation, it will
not continue the top cycle. In this instance, the technician must further inspect the Right Folding Top
Stowage Compartment Lid Closed Position Sensor to determine what the fault is.
Version History
Version
Modi ed
3
12/17/2019 Created on.
10/29/20 - Updated model years for Camaro and Corvette
03/03/2022 - Updated model years.
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