DTC U1040 Loss of Class 2 Communications with ABS. Buick Century (China) (CNG) 1999

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 Body and Accessories 🢒 Data Link Communications 🢒 DTC U1040 Loss of Class 2 Communications with ABS

Circuit Description

Class 2 control modules receive a state of health message from the Electronic Brake Traction Control Module (EBTCM) through the Class 2 serial data link.

Conditions for Setting the DTC

Class 2 control modules do not receive a state of health message from the EBTCM.

Action Taken When the DTC Sets

•	Class 2 control modules store DTC U1040 in memory.

•	The ABS indicator lamp turns on while the fault is present.

Conditions for Clearing the DTC

•	DTC U1040 will clear as a current DTC U1040 and will set as a history DTC U1040 when the class 2 control modules detect a state of health message from the EBTCM.

•	Using a scan tool.

Diagnostic Aids

•	The following conditions may cause an intermittent malfunction to occur:

•	An intermittent open or short to ground in circuit 1122.

•	Poor connections at the EBTCM.

•	An intermittent open in the Splice Pack SP205.

•	The Body Control Module (BCM) may store DTC U1040 if certain diagnostics are performed between the EBTCM and the Data Link Connector (DLC).

•	DTC P1626 will set in the Powertrain Control Module (PCM) when the ignition switch is on with the Body Control Module (BCM) disconnected. When BCM diagnostics and repairs are completed, refer to OBD System Check in Engine Controls for additional information on PCM related DTCs.

Test Description

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

This step checks for an open in the Splice Pack SP205.

This step checks for a short to ground in circuit 1122.

This step checks for a short to B+ in circuit 1122.

This step checks for an open in circuit 1122.

Step

Action

Value(s)

Yes

Turn the ignition switch off.
Disconnect the scan tool from the DLC.
Disconnect battery negative terminal.
Using a DMM, measure the resistance between the SP205 terminal A and each of the SP205 terminals B, E, G, L, and M; one terminal at a time.

Is the resistance measured within the specified range?

Less than 2ohms

Go to Step 2

Go to Step 6

Disconnect the Electronic Brake Traction Control Module (EBTCM) harness connector.
Using a DMM, measure the resistance between the SP205 harness connector terminal E and ground.

Is the resistance measured same as the specified value?

∞

Go to Step 3

Go to Step 7

Reconnect the battery negative terminal.
Turn the ignition switch on.
Using a DMM, measure the voltage between the SP205 harness connector terminal B and ground.

Is the voltage measured within the specified range?

Less than 2V

Go to Step 4

Go to Step 8

Turn the ignition switch off.
Using a DMM, measure the resistance between the SP205 harness connector terminal B and EBTCM harness connector terminal B7.

Is the resistance measured within the specified range?

Less than 5ohms

Go to Step 5

Go to Step 9

Reconnect the EBTCM connector.
Turn the ignition switch on.
Using a scan tool, communicate with the EBTCM.

Does the scan tool communicate with the EBTCM?

Go to Step 11

Go to Step 10

Replace the Splice Pack SP205.

Is the repair complete?

Go to Step 11

Repair short to ground in circuit 1122.

Is the repair complete?

Go to Step 11

Repair short to B+ in circuit 1122.

Is the repair complete?

Go to Step 11

Repair poor connection or open in circuit 1122.

Is the repair complete?

Go to Step 11

•	The integrity of the class 2 serial data link is OK. However, the Electronic Brake Traction Control Module (EBTCM) is not communicating class 2 data due to a fault within the EBTCM.

•	Refer to Diagnostic System Check - ABS in Antilock Brake System for further diagnosis.

Is the action complete?

Go to Step 11

Turn the ignition switch off.
Reinstall connectors/components removed and verify repairs.

Is the action complete?

System OK