Circuit Description
The BCM and the air suspension control unit communicate control and diagnostic information via a controller area network (CAN) communication bus. The BCM monitors CAN operational status by expecting a constant flow of messages from the air suspension control unit. If the BCM fails to receive an expected message from the air suspension control unit, this DTC will set.
Condition for Running the DTC
• The battery voltage is more than 20 volts.
• The ignition switch is ON.
Setting conditions of the DTC
• The BCM detects that the CAN Bus messages from the air suspension control unit are not being received.
Condition for Clearing the DTC
• A current DTC clears when the diagnostic runs and does not fail.
• Use a scan tool to clear the DTC.
Circuit/ System Testing DTC U2112
Step Action Value(s) Yes No
1
Did you perform the Diagnostic System Check
-BCM? —
Go to Step 2
Go to Diagnostic System Check -
BCM
2
1. Install a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Turn ON the ignition, with the engine OFF.
4. Monitor the DTC Information with a scan tool.
Does the DTC fail this ignition?
—
Go to Step 3
Go to Intermittent Conditions
3
Does the scan tool communicate with the air suspension control unit?
—
Go to Step 4
Go to Air Suspension Control
System Check in Section 2A1 Air Suspension Control
System
4
1. Test the CAN Low and High circuits among each control module for the following conditions:
• An open circuit
• A short to ground
• A short to battery or ignition voltage
• A short circuit each other
• High resistance
2. Repair circuit(s) as necessary.
Did you find and correct the condition?
—
Go to Step 6 Go to Step 5
5
Important: Replacement BCM must be programmed.
Replace the BCM. Refer to BCM Replacement.
Did you complete the replacement?
—
Go to Step 6 —
6
1. Reconnect all previously disconnected harness connector(s).
2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Turn ON the ignition, with the engine OFF.
Did the DTC fail this ignition?
—
Go to Step 3 Go to Step 7
7 Observe the DTC Information with a scan tool.
Are there any DTCs that you have not diagnosed? —
Go to DTC List System OK
Step Action Value(s) Yes No
Intermittent
Required preliminary inspection
Before starting the inspection, perform the Diagnostic System Check - Body Control Module (BCM) to verify that DTC is not detected.
Visual inspection
Some of the symptom repair procedures require careful visual and physical inspection. This step is extremely important. Problems may be able to be repaired just by carrying out visual and physical inspections, which leads to saving some valuable time. Ensure that:
• The BCM grounds are clean, tightened, and in their proper location.
• The harness wiring and terminals are properly connected and are not pinched or disconnected.
Intermittent IMPORTANT:
Inspect for improper installation of electronic components if an intermittent defect exists. Inspect the commercial add-on electrical equipment devices, lights, and cellular phones. Verify that no commercial equipment is connected to the keyword 2000 serial data circuit. If you cannot locate an intermittent condition, a cellular phone communication signal may be the cause of the condition.
IMPORTANT:
Even if a problem occurs, most problems are caused by failures in electrical connections or wiring. Perform a careful visual and physical inspection of the connectors that may have abnormalities for the following conditions.
• Defective connection of connectors
• Terminals that are not seated
• Terminals that are damaged or improperly formed Repair or replace connector terminals in the problem circuit in order to ensure proper contact tension.
Remove the terminal from the connector body in order to inspect for poor terminal wire connection.
Road test the vehicle with the DMM connected to the suspected circuit. An abnormal reading that occurs when the malfunction occurs is a good indication that there is a malfunction in the circuit being monitored.
Use a scan tool to detect intermittent failures. The scan tool includes the following kinds of functions.
• Use the "Plot" function of the scan tool to plot selected data parameters. Review this stored information to specify an intermittent defect. Refer to Scan Tool Users Guide for more details.
IMPORTANT:
If the intermittent defect exists from the start and then stalls, test for DTCs relating to the vehicle theft deterrent system. Test for improper installation of electronic equipments such as lights, cellular phones, etc.
IMPORTANT:
The following diagnosis shows possible causes for each symptom. The order of these procedures is not important. If there are no abnormalities in the scan tool readings, proceed in a logical order, starting with items that are easiest to check, or those that are most likely.
In order to determine if a specific vehicle is using a particular system or component, refer to Body Control Module (BCM) in Section 9D Wiring System.
Checks Solutions Definition:
The problem is not currently present but is indicated in DTC History.
Or
There is a customer complaint, but the symptom cannot currently be reproduced because the problem is not DTC related.
Harness/Connector Many of the circuits that are open or shorted intermittently are affected by movement of harnesses/connectors caused by vibration, engine torque, bumps, rough pavement, etc. Test for this type of condition by performing the applicable procedure from the following list.
• Move related connectors and wiring while monitoring the appropriate scan tool data.
• Move related connectors and wiring with the components by using the scan tool to command the components to turn ON/OFF. Observe the operations of the components.
• With the engine running, move related connectors and wiring while monitoring engine operation.
If harness or connector movement affects the data displayed, component/system operation, or engine operation, inspect and repair the harness/connector as necessary.
Electrical Connections or Wiring Defective electrical connections, loose terminals or wiring problems cause most intermittent. Perform the following inspections.
• Inspect for poor mating of the connector halves, or terminals improperly seated in the connector body.
• Inspect for improperly formed or damaged terminals. Test for poor terminal tension.
• Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
• Inspect for corrosion/water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation, with little visible evidence. Look for swollen and stiff sections of wire in the suspected circuits.
• Inspect for wires that are broken inside the insulation.
• Inspect whether there are any pinching caused by the wire of the harness, any open circuits or any wear.
• Ensure that the wiring does not come in contact with hot exhaust components.
Power and Grounds of the Control Module
Power and Grounds of Components
Poor power or ground connections can cause widely varying symptoms.
• Test all control module power supply circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power supply circuits that may also need to be tested. Inspect the connections of the fuses and connectors for the module/components, as well as other intermediate connections between the power source and the module/
components. A test lamp or a DMM may indicate that voltage is present, but neither tests the ability of the circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component.
• Test all of the ground circuits for the system and control module. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the ground connections. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component.
Electromagnetic interference (EMI) and Electrical Noise
Some electrical components/circuits are sensitive to EMI or other types of electrical noise. Inspect for the following conditions:
• Whether harnesses are placed too close to high voltage/high current devices such as injection components, motors, generators, etc. These components may induce electrical noise on a circuit that could interfere with normal circuit operation.
• Improper installation of non-factory or commercial electronic equipments such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell phones, etc. These electronic equipments may lead to an emission related failure while in use, but do not fail when they are not in use.
• Test for any open diodes. Some relays may contain a clamping diode.
• Test the generator for a bad rectifier bridge that may be allowing AC noise into the electrical system.
Duplicating Failure Conditions • If none of the previous tests are successful, attempt to duplicate and/
or capture the failure conditions.
• An alternate method is to drive the vehicle with the DMM connected to a suspected circuit. If there is an abnormality in the measurement value of the DMM when a problem has occurred, it may be possible to specify this problem.
Snapshot of Scan Tool The scan tool can be set up to take a "Snapshot" of the parameters available from the serial data. The "Snapshot" function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool is also equipped with a function for creating graphs, and can graph parameters individually or together with other parameters for the purpose of comparison. The Snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets.
An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further.
Refer to "Scan Tool Users Manual" for more information on the
"Snapshot" function.
Checks Solutions