CTS V6-2.8L (2006)
Diagnostic Aids
The high speed GMLAN serial data bus uses two 120 ohms terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits.
One of the resistors is connected at the transmission control module (TCM) and the other is at the engine control module (ECM). When testing for a
short between high speed GMLAN (+) and (-) a reading of 60 ohms is normal. If the high speed GMLAN serial data is open testing the resistance
between high speed GMLAN (+) and (-) will read about 120 ohms.
The engine will not start when there is a total malfunction of the high speed GMLAN serial data circuits while the engine is not running. The following
conditions may cause a total loss of high speed GMLAN data communication:
-> A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
-> Any of the high speed GMLAN serial data circuits shorted to ground or voltage
-> A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
-> Any of the high speed GMLAN serial data circuits open
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. A partial malfunction in the high speed GMLAN serial data circuits uses a different procedure from a total malfunction of the high speed GMLAN
data circuits. The following modules communicate on the high speed GMLAN serial data circuits:
-> Engine control module (ECM)
-> Transmission control module (TCM)
7. Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data high circuit and the GMLAN serial data low circuit
respectively.
14. The communication malfunction may have prevented diagnosis of the customer complaint.