The U0168 diagnostic trouble code (DTC) signifies a loss of communication between the vehicle's primary computer network, often the Controller Area Network (CAN) bus, and the Vehicle Security Control Module (VSCM). This module is crucial for managing various security functions, including the alarm system, remote keyless entry, and sometimes even immobilizer features. When this communication is disrupted, it can lead to a range of issues, from the security system malfunctioning to potential starting problems.
This lack of communication can stem from various causes, ranging from simple wiring issues to a failing VSCM or even problems within the CAN bus itself. Accurately diagnosing the problem is essential to restoring the vehicle's security functions and ensuring proper operation.
| Component/Symptom | Possible Causes | Diagnostic/Repair Steps |
|---|---|---|
| General U0168 Code | Faulty VSCM, Wiring issues, CAN bus problems, Low Battery Voltage | Check battery voltage, Inspect wiring harnesses and connectors, Scan for other DTCs, Test CAN bus integrity, Check VSCM power and ground, Replace/reprogram VSCM. |
| VSCM Power Supply | Blown fuse, Open circuit in power wire | Check VSCM fuse, Test power wire for voltage, Repair open circuit. |
| VSCM Ground | Corroded ground connection, Open ground wire | Inspect and clean ground connections, Test ground wire for continuity, Repair open ground. |
| CAN Bus Wiring | Damaged CAN bus wires, Short to ground/voltage | Visually inspect CAN bus wires, Test CAN bus resistance, Repair damaged wires or shorts. |
| CAN Bus Communication | Faulty CAN bus module, CAN bus overload | Test CAN bus voltage levels, Disconnect modules one at a time to isolate faulty module. |
| VSCM Internal Failure | Defective VSCM | Replace VSCM, Reprogram VSCM if necessary. |
| Security System Malfunction | Lost communication with VSCM, VSCM failure | Diagnose U0168 code, Check VSCM functionality, Repair/replace VSCM. |
| Remote Keyless Entry Issues | Lost communication with VSCM, VSCM failure | Diagnose U0168 code, Check VSCM functionality, Repair/replace VSCM. |
| Immobilizer Problems | Lost communication with VSCM, VSCM failure, Key transponder issue | Diagnose U0168 code, Check VSCM functionality, Verify key transponder functionality, Repair/replace VSCM. |
| Other Modules Affected | CAN bus issues, Voltage drops | Check CAN bus integrity, Check for voltage drops, Repair CAN bus or address voltage drop issues. |
| Intermittent U0168 Code | Loose connections, Temperature-related issues | Inspect connectors for looseness, Test wiring during temperature changes, Repair loose connections or temperature-related issues. |
| Aftermarket Accessories | Incorrect installation, Interference with CAN bus | Disconnect aftermarket accessories, Test for U0168 code, Reinstall accessories correctly or remove them. |
| Programming Issues | Corrupted VSCM software, Incorrect programming | Reprogram VSCM with correct software. |
| Water Intrusion | Corrosion of connectors/wiring | Inspect connectors and wiring for corrosion, Clean or replace corroded components, Address source of water intrusion. |
| Physical Damage | Damage to VSCM or wiring harness | Inspect VSCM and wiring harness for physical damage, Repair or replace damaged components. |
Detailed Explanations
General U0168 Code: This code indicates a general loss of communication with the VSCM. The first step is to rule out basic issues like low battery voltage. Then, a thorough inspection of the wiring and connectors between the VSCM and the CAN bus is essential. Scanning for other DTCs can provide clues about related problems. Testing the CAN bus integrity with an oscilloscope or multimeter is important to verify the communication network is functioning properly. Finally, checking the VSCM power and ground is crucial before considering replacement or reprogramming of the VSCM.
VSCM Power Supply: The VSCM requires a stable power supply to operate. A blown fuse or an open circuit in the power wire can interrupt this supply. Check the VSCM fuse first using a multimeter. If the fuse is good, test the power wire leading to the VSCM for proper voltage (typically battery voltage). If no voltage is present, trace the wire back to the power source to identify and repair the open circuit.
VSCM Ground: A good ground connection is just as crucial as a good power supply. A corroded ground connection or an open ground wire can prevent the VSCM from functioning correctly. Inspect the ground connections associated with the VSCM for corrosion or looseness. Clean the connections thoroughly. Use a multimeter to test the ground wire for continuity to the vehicle's chassis ground. If there is no continuity, repair the open ground wire.
CAN Bus Wiring: The CAN bus is a network of wires that allows various modules in the vehicle to communicate with each other. Damaged CAN bus wires or a short to ground or voltage can disrupt this communication and trigger the U0168 code. Visually inspect the CAN bus wires for any signs of damage, such as cuts, abrasions, or corrosion. Test the CAN bus resistance between the CAN high and CAN low wires using a multimeter. The resistance should be within the manufacturer's specifications. Repair any damaged wires or shorts.
CAN Bus Communication: Problems within the CAN bus itself, such as a faulty CAN bus module or CAN bus overload, can also cause the U0168 code. Test the CAN bus voltage levels using a multimeter or oscilloscope. The voltage levels should be within the manufacturer's specifications. If the voltage levels are incorrect, disconnect modules one at a time to isolate the faulty module that is interfering with the CAN bus communication.
VSCM Internal Failure: In some cases, the VSCM itself may be defective. Before concluding that the VSCM is faulty, rule out all other possible causes, such as wiring issues and CAN bus problems. If all other tests pass, replace the VSCM with a new or known-good unit. In many cases, the new VSCM will need to be programmed to the vehicle using a scan tool.
Security System Malfunction: Since the VSCM controls the security system, a loss of communication with the module can lead to malfunctions, such as the alarm not arming or disarming correctly. Address the U0168 code by diagnosing the underlying cause. Check the VSCM functionality using a scan tool to see if it is responding to commands. Repair or replace the VSCM as needed.
Remote Keyless Entry Issues: Similar to security system malfunctions, remote keyless entry issues can arise due to lost communication with the VSCM. Diagnose the U0168 code and check the VSCM functionality. Ensure the remote key fobs are properly programmed to the vehicle. Repair or replace the VSCM if necessary.
Immobilizer Problems: The immobilizer system prevents the vehicle from starting unless a valid key is present. Lost communication with the VSCM can affect the immobilizer, preventing the engine from starting. Diagnose the U0168 code and check the VSCM functionality. Verify that the key transponder is functioning correctly and is recognized by the VSCM. Repair or replace the VSCM if necessary.
Other Modules Affected: Because the CAN bus connects multiple modules, a problem with the VSCM can sometimes affect other modules. Check the CAN bus integrity to ensure that all modules are communicating correctly. Check for voltage drops in the system, as this can also affect module communication. Repair the CAN bus or address any voltage drop issues.
Intermittent U0168 Code: An intermittent U0168 code can be particularly challenging to diagnose. Loose connections or temperature-related issues are often the cause. Inspect all connectors associated with the VSCM for looseness or corrosion. Test the wiring while wiggling the harness to see if the code appears. Test the wiring during temperature changes (e.g., using a heat gun or cold spray) to see if the code reappears. Repair any loose connections or temperature-related issues.
Aftermarket Accessories: Incorrectly installed aftermarket accessories can sometimes interfere with the CAN bus and cause the U0168 code. Disconnect any aftermarket accessories that have been recently installed. Test the vehicle to see if the U0168 code disappears. If the code disappears, reinstall the accessories correctly or remove them altogether.
Programming Issues: Corrupted VSCM software or incorrect programming can also lead to the U0168 code. Reprogram the VSCM with the correct software using a scan tool. Ensure that the programming process is followed correctly.
Water Intrusion: Water intrusion can cause corrosion of connectors and wiring, leading to communication problems. Inspect the connectors and wiring associated with the VSCM for corrosion. Clean or replace any corroded components. Address the source of the water intrusion to prevent future problems.
Physical Damage: Physical damage to the VSCM or wiring harness can obviously cause communication issues. Inspect the VSCM and wiring harness for any signs of physical damage, such as cracks, breaks, or cuts. Repair or replace any damaged components.
Frequently Asked Questions
What does the U0168 code mean? It means the vehicle's computer is not communicating with the Vehicle Security Control Module (VSCM).
What are the symptoms of a U0168 code? Symptoms can include security system malfunctions, remote keyless entry issues, or immobilizer problems.
Can a bad battery cause a U0168 code? Yes, low battery voltage can sometimes interfere with communication between modules.
How do I fix a U0168 code? Diagnose the underlying cause by checking wiring, CAN bus, and the VSCM itself, and repair or replace faulty components.
Do I need to reprogram the VSCM after replacing it? In most cases, yes, the VSCM needs to be programmed to the vehicle after replacement.
Conclusion
The U0168 DTC, indicating a loss of communication with the Vehicle Security Control Module (VSCM), requires a systematic approach to diagnosis and repair. By carefully checking the power supply, ground connections, CAN bus integrity, and VSCM functionality, and considering factors like aftermarket accessories and programming issues, you can effectively resolve this issue and restore the vehicle's security functions.