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Home >> Cadillac >> 2007 >> STS Base, 3.6 7, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 2 (Data Link Communication System) >> Diagnostic Information and Procedures >> DTC U2106: Lost Communications With Transmission Control System >> Test Description
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Test Description

WARNING: This page is about a different car, the 2004 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  This DTC sets when a communication fault exists between the ECM and the TCM. Inspect for DTCs U2100, U2102 or U2106. If any of these DTCs are present, diagnose them first.
  2. 3:  If a module is not awake, the modules expecting to receive data cannot detect the presence of the transmitting module.
  3. 7:  The TCM needs time to reset memory.
DTC U2106

Step Action Yes No
Schematic Reference: Data Link Connector (DLC) Schematics 
Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views
1 Did you perform the Diagnostic System Check for the system exhibiting the symptom? Go to Step 2  Go to Control Module References in Body Control System for the applicable diagnostic system check
2 
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, monitor the DTC Information for DTC U2100 or DTC U2106.
Does the scan tool indicate that DTC U2100 or DTCs U2106 as either current or history DTCs?		 Go to Diagnostic Trouble Code (DTC) List  Go to Step 3 
3  Test the following circuits of the TCM for an open or high resistance:
  1. The battery positive voltage circuits
  2. The ignition positive voltage circuits
  3. The ground circuits

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 7  Go to Step 4 
4 Test the controller area network (CAN) serial data low circuit and the CAN serial data high circuit between the engine control module (ECM) and transmission control module (TCM) for the following conditions:
  • Open circuit
  • Short to voltage
  • Short to ground
  • Shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 7  Go to Step 5 
5 Inspect for poor connections at the harness connector of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 7  Go to Step 6 
6
IMPORTANT: Perform the set-up procedure for the replaced control module, if required.
Replace the control module that is not communicating. Refer to Control Module References in Body Control System.Did you complete the replacement?		 Go to Step 7  -
7 
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition switch.
  3. Wait at least 10 seconds.
  4. Turn the ignition ON, with the engine OFF.
  5. Retrieve DTCs from the ECM and TCM.
Does the DTC reset?		 Go to Step 2  System OK
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