2015 Camaro Intermittent Failure
Posted to Technical Discussion Forum on 2/5/2016
36 Replies
I have had a 2015 Camaro in the shop for about a week now
with an intermittent problem. The customer purchased the car
from another dealer who can't repair it and told the
customer that the failure would have to become more obvious
to be diagnosed. She called Chevrolet to complain and the
zone told her to bring it to us.
The car has 4000 miles with a problem that is very
intermittent. To duplicate it, the customer states that the
vehicle has to be left overnight in cold weather and,
directly after starting, needs to be driven very rapidly
across railroad tracks. When these conditions are met, the
red brake light on the dash will flash on and off 1 time and
will not re-occur again until sitting overnight again in
cold weather. We're in Florida and cold weather is not easy
to come by.
We gave her a loaner and told her that we needed the car for
two weeks. The first 4 days were warm but I tried driving
the car anyway. We have a railroad crossing about 1/2 mile
from the shop. The problem didn't occur and no codes were
set in any module. (They may have been cleared by the
selling dealer)
The next day turned cold and I drove the car over the tracks
almost fast enough to launch it. The red brake light did
flash 1 time....Wow. Rescanning the modules, the BCM set a
history code for lost communication with the EBCM...A CLUE.
Well, that takes a lot of possibilities out of the picture.
It sounds like a data transmission problem. I hooked up a
laptop to the DLC to monitor the LAN with the GM testing
tool and let the car sit for 4 hours then tried the tracks
again. This is the main high speed LAN on terminals 6 and
14.
[2015 Chevrolet Camaro LT, ECM/Inputs/Outputs Waveform]
The light flashed again and this waveform shows no obvious
problem. The EBCM resides on two LANs, the main LAN and the
chassis expansion LAN. A com problem on either LAN can cause
communication losses with the BCM. I let it sit overnight
and tried it again with the LAN tool watching the chassis
expansion bus on terminals 12 and 13. The light actually
flashed twice this time and I see why.
[2015 Chevrolet Camaro LT, ECM/Inputs/Outputs Waveform]
I would expect to find a loose wire or terminal. Temperature
can cause expansion or contraction as well making the
condition worse. The chassis expansion bus leads from the
EBCM through the firewall to the steering angle sensor and
the multi-axis acceleration sensor. How do we decide what to
test? The LAN is a two wire twisted pair. Looking at the
failure, both LAN+ and LAN- dropped out and resumed exactly
at the same time. What's the odds of that? Not very good.
The EBCM could be losing power or ground, but in that case,
I would expect the multi-axis sensor to have stored a
communications code as well. What's next? Well, all high
speed modules need a independent communications enable 12
volt circuit for wake up. The EBCM com enable circuit is
shared with other modules through a splice connector, J202
but is fed independently through one branch that goes
through connector X104, terminal 1 under the hood. I
back-probed terminal 1 with a voltmeter in min/max mode and
drove around the lot hitting speed bumps as hard as I could
and I saw drops from battery voltage on my meter over the
bumps. Good - CLUE 2.
The J202 splice connector is in the dash wiring harness just
below the inside fuse block. I was able to reach up under
the dash and squeeze and wiggle the harness in this area
while watching the waveforms on terminals 12 and 13 and saw
drop-outs occur. I cut open the harness to expose the splice
connector, circuit 5986 and cut off the splice tape. I found
bare wires lying side by side without a crimp splice
installed, just splice tape. Nice factory wiring job. I
soldered the splice and retaped the harness. The next two
days, I drove the car under similar conditions and saw
this....
[2015 Chevrolet Camaro LT, ECM/Inputs/Outputs Waveform]
The vehicle is repaired and gone and the customer is
overjoyed. The threat of a buy back is eliminated and we
grew a new customer.
James from Florida
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