For 1990-2009 cars
Data Link Communications Components
Cell 50 EBTCM and TCM CAN Interface

### Circuit Description

The Controller Area Network (CAN) serial data circuit is a high speed serial data bus used to communicate information between the Electronic Brake and Traction Control Module (EBTCM), the Engine Control Module (ECM) and the Transmission Control Module (TCM). When the ignition switch is turned to the ON position, the modules begin to transmit data between each other. The following data is transmitted and received between the ECM and TCM:

• | Brake Switch signal from the ECM to the TCM

• | Throttle Position Angle from the ECM to the TCM

• | Engine Speed signal from the ECM to the TCM

• | Engine Coolant Temperature from the ECM to the TCM

• | Engine Torque signal from the ECM to the TCM

• | MIL Request signal from the TCM to the ECM

The following data is transmitted and received between the ECM and EBTCM:

• | Requested Torque from the EBTCM to the ECM

• | Delivered Torque from the ECM to the EBTCM

• | Engine Speed (RPM) from the ECM to the EBTCM

The addressing scheme employed with CAN assigns a label to every message, with each message receiving a unique "identifier". The identifier classifies the content of the message (such as engine speed). Each module processes only those messages whose identifiers are stored in the module's acceptance list. This is CAN's form of message filtering.

The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.

### Conditions for Running the DTC

The CAN Bus circuit is monitored continuously after the ignition switch is turned to the ON position.

### Conditions for Setting the DTC

Each controller on the CAN Bus monitors the CAN Bus circuit for the following malfunctions:

• | The CAN Bus high and low circuits are shorted together.

• | The CAN Bus high or low circuit is shorted to ground.

• | The CAN Bus high or low circuit is shorted to voltage.

### Action Taken When the DTC Sets

The following describes the action taken when the code is set in a particular control module.

#### Engine Control Module

• | The Malfunction Indicator Lamp (MIL) is illuminated on the second consecutive drive trip that the diagnostic runs and fails.

• | The ECM records the operating conditions at the time the DTC is set in the Freeze Frame.

#### Transmission Control Module

• | The Service Transmission Lamp (STL) is illuminated.

• | The TCM sends a MIL request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.

• | The transmission operates in the Default Mode:

- | Maximum line pressure

- | Command 4th gear

- | Inhibit TCC

- | Freeze shift adapts

#### Electronic Brake Traction Control Module

• | A malfunction DTC is stored.

• | TCS is disabled.

• | The TC indicator is illuminated.

### Conditions for Clearing the MIL/DTC

The following describes the conditions for clearing the MIL/DTC in a particular control module.

#### Engine Control Module

• | The condition for the DTC is no longer present. The ECM turns off the MIL after 3 consecutive drive trips that the diagnostic runs and passes.

• | The scan tool clear DTC function is used.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.

• | The ECM battery voltage is interrupted.

#### Transmission Control Module

• | The condition for the DTC is no longer present. The TCM turns off the STL.

• | The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL request.

• | The scan tool clear DTC function is used.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.

• | The TCM cancels the DTC Default Mode actions when the malfunction no longer is present and the ignition switch is off long enough to power down the TCM.

#### Electronic Brake Traction Control Module

• | The condition for the DTC is no longer present.

• | The scan tool clear DTC function is used.

• | A history DTC clears after 100 ignition cycles pass with no malfunction detected.

### Diagnostic Aids

The malfunction for this DTC will be limited to the control module that the DTC was set in, and the CAN Bus circuit(s) and controller(s) that are connected to the control module the DTC was set in.

It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.

Use the Connector Test Adapter Kit J 35616 for any test that requires probing the ECM or TCM harness connector. Using this kit will prevent damage to the harness connector terminals.

Thoroughly inspect any circuitry that may be causing the complaint for the following conditions:

• | Poor connection at the control module the code was set in or at the connected control module(s). Inspect the harness connectors for the following conditions:

- | Backed out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Poor terminal to wire connection.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harness. A change in the display may help to locate the malfunction.

• | The following conditions may cause an intermittent malfunction:

- | A poor connection

- | Rubbed-through wire insulation

- | A broken wire inside the insulation

If an intermittent malfunction exists, refer to Intermittents and Poor Connections Diagnosis in Wiring Systems for further diagnosis.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. At this point, the most likely cause of the malfunction is the ECM, TCM or the EBTCM. This test will determine through process of elimination which module is causing the malfunction.

2. Because of the previous testing, the modules on the CAN Bus circuit may have set other CAN Bus DTCs. You must clear or diagnose the DTCs from these modules to avoid future misdiagnosis.

#### DTC U2100 CAN Bus Communications Malfunction

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Data Link Communications Diagnostic System Check performed? | -- | Go to Step 2 | Go to Diagnostic System Check - Data Link Communications
2 | Test the CAN Bus High and Low circuits for a short to ground between the ECM and TCM. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Diagnostic System Check - Data Link Communications | Go to Step 3
3 | Test the CAN Bus High and Low circuits for a short to ground between the ECM and EBTCM. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Diagnostic System Check - Data Link Communications | Go to Step 4
4 | Test the CAN Bus circuits for the CAN Low and CAN High shorted together between the ECM and TCM. Refer to Wiring Repairs in Wiring Systems Did you find and correct the condition? | -- | Go to Diagnostic System Check - Data Link Communications | Go to Step 5
5 | Test the CAN Bus circuits for the CAN Low and CAN High shorted together between the ECM and EBTCM. Refer to Wiring Repairs in Wiring Systems Did you find and correct the condition? | -- | Go to Diagnostic System Check - Data Link Communications | Go to Step 6
6 | Test the CAN Bus High and Low Circuits for a short to voltage between the ECM and TCM. Refer to Wiring Repairs in Wiring Systems Did you find and correct the condition? | -- | Go to Diagnostic System Check - Data Link Communications | Go to Step 7
7 | Test the CAN Bus High and Low Circuits for a short to voltage between the ECM and EBTCM. Refer to Wiring Repairs in Wiring Systems Did you find and correct the condition? | -- | Go to Diagnostic System Check - Data Link Communications | Go to Step 8
8 |

1. Reconnect all previously disconnected components.
2. Using the scan tool clear the DTC from the ECM, TCM and EBTCM.
3. Turn the ignition switch to the OFF position.
4. Disconnect the TCM and EBTCM.
5. Turn the ignition switch to the ON position, with the engine off.
6. Using the scan tool, select the Display DTCs function for the ECM.

Does DTC U2100 reset as a current DTC?

--

Go to Step 9

Go to Step 10

9 | Replace the ECM. Refer to Engine Control Module Replacement/Programming in Engine Controls 3.0L. Is the replacement complete? | -- | Go to Step 13 | --
10 |

1. Turn the ignition switch to the OFF position.
2. Reconnect the TCM.
3. Turn the ignition switch to the ON position, with the engine off.
4. Using the scan tool, select the Display DTCs function for the TCM and ECM.

Does the DTC U2100 reset as a current DTC in the TCM or ECM?

--

Go to Step 11

Go to Step 12

11 | Replace the TCM. Refer to Transmission Control Module Replacement in Automatic Transmission 4L30-E. Is the replacement complete? | -- | Go to Step 13 | --
12 | Replace the EBTCM . Refer to Electronic Brake and Traction Control Module Replacement in Antilock Brake System. Is the replacement Complete? | -- | Go to Step 13 | --
13 |

1. Reconnect all of the disconnected modules
2. Install the scan tool.
3. Turn the ignition switch to the ON position with the engine off.
4. Select the Display DTCs function for each module on the CAN Bus.

Does the scan tool display any DTCs which begin with U21 and with a current status?

--

Go to Step 14

Go to Step 15

14 | Diagnosis the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Did you complete the action? | -- | Go to Step 15 | --
15 | Clear the DTCs using the scan tool. Did you complete the action? | -- | System OK | --