Posted to Technical Discussion Forum on 6/20/2012
53 Replies
One of the younger techs in the shop had a problem that
seemed interesting today. The customer was driving down the
road and heard a "pop' noise and all the warning lamps in
the IPC came on, the gauges were inop, the A/C stopped
working, the seats and windows were inop and the radio
stopped playing. Other items may have been inop as well.
He scanned the control module system and had communication
with only the ECM and the TCM. The ECM set U1301-00 and
U1041-00. The TCM did not code. He asked me where he should
go next. I told him to test resistance at the ALDL between 6
and 14 and between 2 and 4 with the key off after waiting 2
minutes. He said 6 & 14 had 60.1 ohms and 2 & 4 read
open. OK - I told him next to pull the JX205 Class 2 splice
connector and ck the resistance and pin fit on the purple
wire from the ALDL to the splice connector. He said it was
OK.
Hmmm - Next I told him to check each pin in the splice
connector for resistance to ground. He said all had
resistances in the kilohm to megohm range except pin H which
leads to the rear body JX306 splice connector. He said this
pin read open. OK, something isn't right here. Now I needed
to walk over to the car and look for myself.
Pin H at the JX205 connector did read open. I then switched
my DVOM to voltage and read a steady 6.92 volts. That's why
he was confused that it read open with no Class 2
communications. I unplugged the rear splice connector and
checked each pin for voltage. Pin A to the VCIM read almost
7 volts, full Class 2 voltage. Unplugging the VCIM, the
voltage dropped to 0 and full communication was restored and
all functions except OnStar was resumed.
The VCIM was back-feeding voltage into the Class 2 network
even with the key off, causing the failure. He just didn't
understand how he lost all class 2 communications due to an
"open" circuit to one module.
James from Florida
53 Replies Received
(View Replies)
53 Replies Received
(Hide Replies)
|