Scan Tool Does Not Communicate with Class 2 Device. Cadillac CTS

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2003 🢒 CTS - RHD 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 Scan Tool Does Not Communicate with Class 2 Device

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

Diagnostic Aids

The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:

•	A class 2 serial data circuit shorted to ground.

•	A class 2 serial data circuit shorted to voltage.

•	An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

Test Description

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

A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.

The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.

A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.

Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.

Disconnecting the splice packs one at a time and attempting to communicate with any module still connected to the class 2 serial data circuit, will determine whether or not the concern is in the star portion of the class 2 serial data circuit.

Connecting the class 2 serial data circuits to the suspect splice pack one at a time while attempting to communicate with any module still connected to the class 2 serial data circuit, will determine which circuit or module on the star is causing the concern.

Splitting the class 2 serial data circuit will help isolate the location of the malfunction. If communication can be established, the concern is located in the wiring or one of the modules that is no longer connected to the DLC. If communication cannot be established, the concern is located in the wiring or one of the modules that is still connected to the DLC.

If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.

The communication concern may have prevented diagnosis of the customer complaint.

Step

Action

Yes

Schematic Reference: Data Link Connector Schematics

Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

Turn ON the ignition, with the engine OFF.
Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 3

Go to Step 8

Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
Record all of the displayed DTCs, the DTC status and the module which set the DTC.

Did you record any DTCs in the range of U1000 to U1305?

Go to Step 4

Go to Step 7

Are history DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

Important:: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.

Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following in Wiring Systems:

•	Testing for Intermittent Conditions and Poor Connections

•	Circuit Testing

•	Connector Repairs

•	Wiring Repairs

Did you find and correct the condition?

Go to Step 21

Go to Step 6

Are U1000 or U1255 the only DTCs displayed in the previously specified range?

Go to DTC U1000 and U1255

Go to DTC U1001-U1254

Diagnose the non-communicating module by using the DTC U1001--U1254 Lost Communications with XXX procedure for the module which is not communicating. The DTC U1001--U1254 Lost Communications with XXX procedure will determine which module is not communicating. Refer to DTC U1001-U1254 .

Did you complete the action?

Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check

Turn OFF the ignition.
Disconnect the scan tool from the data link connector (DLC).
Inspect for poor connections and terminal tension at the DLC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check

Go to Step 9

Test the ground circuits of the DLC for an open or high resistance. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check

Go to Step 10

Isolate the power mode master (PMM) module from all other modules on the class 2 serial data circuit. To identify which module is the PMM refer to Body Control System Description and Operation in Body Control Systems.
Attempt to communicate with the PMM.

Does the scan tool communicate with the PMM?

Go to Step 12

Go to Step 11

Test the class 2 serial data circuits between the DLC and the PMM for the following conditions. Turn ON the ignition when testing for a short to voltage:

•	High resistance

•

Open

•	Short to ground

•	Short to voltage

Test the following circuits of the PMM for an open or high resistance:

•	The battery positive voltage input circuits

•	The battery positive voltage output circuits

•	The ignition voltage input circuits

•	The ignition voltage output circuits

•	The switched battery positive voltage supply circuits

•	The ground circuits

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

Connect the previously disconnected modules.
Perform the following for each splice pack, in order to determine if the concern is located within the class 2 serial data circuits or the modules connected to the splice packs:

2.1.	Turn OFF the ignition.

2.2.	One at a time disconnect each splice pack which connects the modules to the star portion of the class 2 serial data circuit, by removing the splice pack comb.

2.3.	Turn ON the ignition, with the engine OFF.

2.4.	Attempt to communicate with any module still connected to the class 2 serial data circuit after disconnecting each splice pack.

Does the scan tool communicate with any module still connected to the class 2 serial data circuit after all the splice packs have been disconnected?

Go to Step 13

Go to Step 14

Using the appropriate jumper at the suspect splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:

Turn ON the ignition, with the engine OFF.
Connect each previously disconnected module to the class 2 serial data circuit one at a time until communication with the class 2 serial data circuit is lost.

Did you complete the action?

Go to Step 18

Turn OFF the ignition.
Split the class 2 serial data circuit in half by disconnecting 2 modules in order to help isolate the location of the concern within the class 2 serial data circuit. The DLC must remain connected to at least 1 module and the PMM.
Turn ON the ignition, with the engine OFF.
Attempt to communicate with any module still connected to the class 2 serial data circuit.

Does the scan tool communicate with any module still connected to the class 2 serial data circuit?

Go to Step 16

Go to Step 15

The concern is located within the ring portion of the class 2 serial data circuit still connected to the DLC. Perform the following, one module at a time starting at the module furthest from the DLC, for each module on the class 2 serial data circuit now attached to the DLC.

Turn OFF the ignition.
Disconnect the furthest module from the DLC still connected to the class 2 serial data circuit.
Turn ON the ignition, with the engine OFF.
Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.
Repeat steps 1 through 4 above until communication is restored.

Does the scan tool communicate with any module still connected to the class 2 serial data circuit?

Go to Step 18

Go to Step 17

The concern is located within the ring portion of the class 2 serial data circuit that is not connected to the DLC.

Connect one of the modules that was disconnected to split the serial data circuit.
Perform the following, one module at a time starting at the module furthest from the DLC, for each module on the class 2 serial data circuit now attached to the DLC.

2.1.	Turn OFF the ignition.

2.2.	Disconnect the furthest module from the DLC still connected to the class 2 serial data circuit.

2.3.	Turn ON the ignition, with the engine OFF.

2.4.	Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.

2.5.	Repeat steps 2.1 through 2.4 until communication is restored.

Does the scan tool communicate with any module still connected to the class 2 serial data circuit?

Go to Step 18

Go to Step 17

Repair short to ground or voltage condition in the class 2 serial data circuits or in-line connectors to the last module disconnected in the branch being diagnosed. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

Test the class 2 serial data circuits connected to the suspect module for a short to ground or a short to voltage.

Turn ON the ignition with the engine OFF when testing for a short to voltage.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 21

Go to Step 19

Inspect for poor connections and terminal tension at the harness connector of the suspect module. 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 21

Go to Step 20

Important: Perform the module programming or setup procedure if required.

Replace the suspect module. Refer to Control Module References in Body Control System for the appropriate repair instructions for module replacement.

Did you complete the replacement?

Go to Step 21

Connect all of the modules.
Connect all the connectors.
Install a scan tool.
Turn ON the ignition leaving the engine OFF.

Important: The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn off or disconnect the scan tool before you display DTCs.

Wait for 10 seconds.
Select the display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
Record all of the displayed DTCs and the DTC status.

Did your record any DTCs which begin with a letter U and with a current status?

Go to Step 23

Go to Step 22

Did you record any DTCs which do not begin with a letter "U"?

Go to Step 23

Go to Step 24

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or concern.

Did you complete the action?

Go to Step 24

Did you diagnose all of the DTCs?

Go to Step 25

Go to Step 23

Clear the DTCs using the scan tool.

Did you complete the action?

Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check