For 1990-2009 cars

### Circuit Description

Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. Each module on GMLAN network maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255 the controller removes itself from the network and a DTC U2100 will be set.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC U2100 Controller Area Network (CAN) Bus Communication

This vehicle has DTCs which include DTC Symptoms. The DTC symptom descriptions for symptoms 71 and 72 are exceptions for this vehicle and differ from what is described on DTC Symptom Description. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom | DTC Symptom Descriptor
--- | ---
00 | No Additional Information
71 | Low Speed Bus Error
72 | High Speed Bus Error

### Conditions for Running the DTC

• | Voltage supplied to the module is in the normal operating voltage range.

• | The vehicle power mode requires serial data communication to occur.

### Conditions for Setting the DTC

A certain number of no valid transmitted messages on the GMLAN serial data circuits are detected by the module.

### Action Taken When the DTC Sets

• | The module suspends all message transmission.

• | The module uses default values for all parameters received on the GMLAN serial data circuits.

• | The module inhibits the setting of all other GMLAN communication DTCs for the respective bus.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | When the ignition cycle counter has reached the newly set threshold and no trouble occurs repeatedly, the history DTC will be cleared.

### Diagnostic Aids

#### U2100 72

• | This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with High Speed GMLAN Device. Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device .

• | An intermittent condition is likely to be caused by a short on the high speed high speed GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with High Speed GMLAN Device procedure in order to isolate an intermittent condition. Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device .

#### U2100 71 and U2100 00

These DTCs can be retrieved from instrument panel module (IPM) with a current status. Refer to the table below to diagnose it. DTC U2100 00 can be retrieved with a current status only it was set for low speed GMLAN link. If set for high speed GMLAN link, see U2100 72.

### Test Description

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

1. The low speed serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the splice pack SP303 serial data circuits.

2. The low speed serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the splice pack SP300 serial data circuits.

3. This test isolates the splice pack SP201 serial data circuits.

4. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

5. The communication malfunction may have prevented diagnosis of the customer complaint.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Data Communication Schematics Connector End View Reference: Master Electrical Component List
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn ON the ignition, with the engine OFF.
2. Retrieve DTCs from the instrument panel module (IPM).

Is U2100 71 and/or U2100 00 set as current?

Go to Step 4

Go to Step 3

3 | Important: Turn ON the ignition, with the engine OFF to test a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions Test the low speed GMLAN serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following:

• | Testing for Intermittent Conditions and Poor Connections

• | Circuit Testing

• | Connector Repairs

• | GMLAN Wiring Repairs

Did you find and correct the condition?

Go to Step 18

--

4 |

1. Turn OFF the ignition.
2. Disconnect the splice pack SP303.
3. Turn ON the ignition, with the engine OFF.
4. Retrieve the DTCs from the IPM.

Is U2100 71 and/or U2100 00 set as current?

Go to Step 7

Go to Step 5

5 | Repeat the following steps on the low speed GMLAN serial data circuits connected to the splice pack SP303 until the concern is located:

1. Turn OFF the ignition.
2. Using the correct terminal adapter, connect a jumper wire to the inflatable sensing and diagnostic module (SDM) terminal of the splice pack SP303.
3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the rest of devices connected to splice pack SP303.
4. Turn ON the ignition, with the engine OFF.
5. Retrieve DTCs from the IPM.

Is U2100 71 and/or U2100 00 set as current?

Go to Step 6

--

6 |

1. Turn OFF the ignition.
2. Disconnect the module that caused the no communication condition.
3. Test the low speed GMLAN serial data circuit between the splice pack SP303 and the respective 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 GMLAN Wiring Repairs .
4. Test the ground circuits of the suspected module for an open.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

7 |

1. Turn OFF the ignition.
2. Disconnect the splice pack SP300.
3. Turn ON the ignition, with the engine OFF.
4. Retrieve the DTCs from the IPM.

Is U2100 71 and/or U2100 00 set as current?

Go to Step 10

Go to Step 8

8 | Repeat the following steps on the low speed GMLAN serial data circuits connected to the splice pack SP300 until the concern is located:

1. Turn OFF the ignition.
2. Using the correct terminal adapter, connect a jumper wire to the splice pack SP201 terminal of the splice pack SP300.
3. Connect the other end of the jumper wire, using correct terminal adapter, to the terminal for the devices connected to splice pack SP300.
4. Turn ON the ignition, with the engine OFF.
5. Retrieve the DTCs from the IPM.

Is U2100 71 and/or U2100 00 set as current?

Go to Step 9

--

9 |

1. Turn OFF the ignition.
2. Disconnect the module that caused the no communication condition.
3. Test the low speed GMLAN serial data circuit between the splice pack SP300 and the respective 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 GMLAN Wiring Repairs .
4. Test the ground circuits of the suspected module for an open.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

10 |

1. Turn OFF the ignition.
2. Disconnect the splice pack SP201.
3. Turn ON the ignition, with the engine OFF.
4. Retrieve the DTCs from the IPM.

Is U2100 71 and/or U2100 00 set as current?

Go to Step 13

Go to Step 11

11 | Repeat the following steps on the low speed GMLAN serial data circuits connected to the splice pack SP201 until the concern is located:

1. Turn OFF the ignition.
2. Using the correct terminal adapter, connect a jumper wire to the IPM terminal of the splice pack SP201.
3. Connect the other end of the jumper wire, using correct terminal adapter, to the rest of circuits connected to splice pack SP201.
4. Turn ON the ignition, with the engine OFF.
5. Retrieve the DTCs from the IPM.

Is U2100 71 and/or U2100 00 set as current?

Go to Step 13

--

12 |

1. Turn OFF the ignition.
2. Disconnect the module that caused the no communication condition.
3. If the DTC was caused by the low speed GMLAN circuit between SP201 and SP300, repair the circuit for a short to ground or a short to voltage.
4. Test the low speed GMLAN serial data circuit between the splice pack SP201 and the respective 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 GMLAN Wiring Repairs .
5. Test the ground circuits of the suspected module for an open.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

13 |

1. Turn OFF the ignition.
2. Disconnect the IPM.
3. Test the both low speed GMLAN serial data circuits of the IPM for a short to ground, a short to voltage or an open. Turn ON the ignition, with the engine OFF when testing for a short to voltage. Refer to Circuit Testing and GMLAN Wiring Repairs .
4. Test the ground circuits of the IPM for an open.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

14 | Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 15 | --
15 |

1. Reconnect all of the disconnected modules.
2. Reconnect any other disconnected connectors.
3. Install a scan tool.
4. Turn ON the ignition, with the engine OFF.
5. Retrieve DTCs using Vehicle DTC Information feature on the scan tool, under Computer/Integrating System menu.

Is there any DTC which begin with a U and a current status?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 16

16 | Is there any DTC which does not begin with a U recorded? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 17
17 | Have you any DTCs not diagnosed? | Go to Step 18 | Go to Step 15
18 | Clear the DTCs with the scan tool. Is the operation completed? | System OK | --