The OBD-II trouble code U0155 indicates a communication fault within your vehicle’s network. Specifically, it signals “Lost Communication with Instrument Panel Control (IPC) Module.” This means that the IPC module, commonly known as the instrument cluster or dashboard, is not communicating effectively with other control modules in the car’s system. This communication breakdown can disrupt the normal operation of various vehicle functions and may trigger warning lights. Understanding the U0155 code is crucial for diagnosing and resolving issues related to your vehicle’s communication network and instrument panel.
Symptoms of a U0155 Code
When your vehicle logs a U0155 code, you might observe several symptoms. These can range from subtle anomalies to more noticeable malfunctions within your car’s instrument panel and overall system. Here are some common symptoms associated with the U0155 error code:
- Malfunction Indicator Lamp (MIL) is illuminated: This is often the first and most obvious sign. The check engine light or MIL will turn on, alerting you to a potential problem.
- Instrument Panel Indicator Lights Issues: You may experience a scenario where all the indicator lights on your instrument panel illuminate simultaneously. Conversely, in other cases, none of the indicator lights might come on at all. This erratic behavior of the instrument cluster is a key symptom.
- Scan Tool Communication Problems: When a U0155 code is active, your OBD-II scan tool may struggle to communicate with the vehicle’s modules, or specifically with the IPC module. This can hinder further diagnostic efforts.
Common Causes of U0155
The U0155 code points towards a communication problem, and several factors can cause this loss of communication with the IPC module. Identifying the root cause is essential for effective repair. Here are the typical culprits behind a U0155 code:
- CAN Bus Circuit Issues: The most frequent causes involve problems within the Controller Area Network (CAN) bus system. This includes:
- Open Circuit in CAN Bus + or – circuit: A break in the wiring of either the CAN bus positive or negative circuit can disrupt communication.
- Short Circuit in CAN Bus + or – circuit: A short to power or ground in either CAN bus circuit can also lead to communication failure.
- Faulty Control Module (Rare): While less common, a malfunctioning IPC module itself can be the cause. However, other simpler issues are more likely to be the problem before suspecting a faulty module.
Diagnosing and Repairing the U0155 Code
Troubleshooting a U0155 code requires a systematic approach. Here’s a step-by-step guide to help you diagnose and potentially resolve the issue:
Preliminary Checks
- Check for Technical Service Bulletins (TSBs): Always start by checking for TSBs related to your vehicle’s make and model. Manufacturers often issue TSBs for known issues, which can provide a quicker fix.
- Check for Other Diagnostic Trouble Codes (DTCs): Note if there are any other DTCs present. Prioritize diagnosing any codes related to bus communication, VIN issues, or battery/ignition problems first. Addressing these basic codes might resolve the U0155 indirectly.
- Scan Tool Communication Test: Attempt to communicate with the IPC module using your scan tool.
- If you can communicate with the IPC module and U0155 is the only code from other modules, the U0155 might be intermittent or a stored memory code.
- If you cannot communicate with the IPC module, the U0155 code is active, indicating a current problem.
Power and Ground Checks for IPC Module
Loss of power or ground is a common cause of communication issues.
- Inspect Fuses: Check all fuses that supply power to the IPC module. Refer to your vehicle’s wiring diagram or owner’s manual for fuse locations.
- Inspect Grounds: Locate and inspect all ground connections for the IPC module. Ensure they are clean and tightly secured. If necessary, disconnect, clean with a wire brush and baking soda solution, and re-tighten the connections.
CAN Bus Circuit Testing
If power and ground are confirmed to be good, focus on the CAN bus circuits.
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Connector and Wiring Inspection:
- Disconnect the negative battery cable before working on electrical connectors.
- Locate the IPC module connector, usually behind the instrument panel.
- Visually inspect the connectors and wiring for any signs of damage like scraping, rubbing, bare wires, burns, or melted plastic.
- Carefully inspect the terminals inside the connectors for corrosion or burn marks. Clean terminals with electrical contact cleaner and a plastic bristle brush if needed, and apply dielectric silicone grease upon reassembly.
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Voltage Checks on CAN Bus Circuits: Use a digital volt-ohmmeter (DVOM) to perform voltage checks. You’ll need a wiring diagram for your specific vehicle to identify the CAN bus circuits (CAN C+/-, CAN C-, CAN B+, CAN B-).
- Power and Ground Verification at IPC Module: With the IPC module disconnected but battery reconnected, check for power and ground at the IPC module connector pins using the DVOM. Verify battery voltage where power is expected and continuity to ground where ground is expected.
- CAN Bus Voltage Readings (Key On, Engine Off):
- CAN C+ (or HSCAN +): Expect to see approximately 2.6 volts, fluctuating slightly.
- CAN C- (or HSCAN -): Expect to see approximately 2.4 volts, fluctuating slightly.
- CAN B+ (or MSCAN +): Expect to see approximately 0.5 volts, fluctuating slightly.
- CAN B- (or MSCAN -): Expect to see approximately 4.4 volts, fluctuating slightly.
If voltage readings are significantly different or absent, it indicates a problem in the CAN bus wiring.
Seeking Professional Automotive Diagnostic Help
If all the above tests pass and the U0155 code persists, or if you are not comfortable performing these diagnostic steps, it’s advisable to seek assistance from a trained automotive diagnostician. A persistent U0155 code after thorough checks might indicate a faulty IPC module, which may require replacement and programming or calibration to the vehicle’s system for proper function.
Disclaimer: This information is for informational purposes only and is not intended as professional repair advice. We are not liable for any actions taken on your vehicle based on this information. Always consult with a qualified automotive technician for diagnosis and repairs.
