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U0155 Severity
Once the vehicle's onboard system no longer detects the issue, most codes will disappear on their own. If your vehicle still has this code, however, it should be properly diagnosed to avoid a more serious problem.
For a proper diagnosis, RepairPal Certified shops have the equipment, tools, and expertise.
Moderate severity codes might not threaten the vehicle's safety or functionality immediately, but you should still get it diagnosed within a reasonable time frame to keep your car running well.
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Code U0155 stands for Lost Communication with Instrument Panel Cluster.
The instrument cluster houses the vehicle gauges and warning lights. Modern instrument clusters are very advanced. The instrument cluster communicates with computers throughout the vehicle via the controller area network (CAN) bus. In some cases, the instrument cluster acts as a gateway on the CAN bus. The instrument cluster may also perform additional tasks such as acting as an interface to the anti-theft system.
All of a vehicle's computers (referred to as modules) share and receive information over the CAN bus. Two lines make up the bus: CAN High and CAN Low. They are referred to as high and low because of their data rates. CAN high has a communication rate of 500k bits/second, whereas CAN Low has a rate of 125k bits/second. Since communication over the bus is bi-directional, terminating resistors must be used. There are two terminating resistors, one at each end of the CAN bus.
Code U0155 indicates the instrument cluster is not receiving or transmitting messages on the CAN bus.
Instrument cluster / Image source
Get it diagnosed by a professional
Code U0155 is typically caused by one of the following:
Sometimes U0155 can pop up intermittently, or it can result from a dead battery. This is especially true if the code is a history code and not current. Clear the code and see if it returns. If it does, the next step is to perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.
The instrument cluster can't communicate properly without sufficient battery voltage. Test and recharge or replace the battery as needed. Then, clear the code.
Diagnostic trouble codes (DTCs) set for multiple modules indicate a potential problem with the CAN network. In this case, a professional will begin by checking network integrity, instead of focusing on the instrument cluster.
The CAN bus can be checked for defects including shorts, high resistance and opens. This process is typically started at the data link connector. The data link connector has 16 pins, with pins 6 and 14 being CAN high and CAN low. A digital multimeter (DMM) is connector to one or both of these pins for testing. If a problem is found, further testing is done to isolate and repair the concern.
An alternate way to check the CAN bus is with a breakout box. This box is used to monitor CAN bus communication and identify problems. It connects directly to the data link connector. The two CAN bus terminating resistors can also be check with a DMM at the data link connector. This is done with the DMM connected between pins 6 and 14 of the connector. A reading of 60 ohms indicates the resistors are intact.
Now it's time to start focusing on the instrument cluster. The first thing a technician will do is attempt to communicate with the cluster via a diagnostic scan tool. This tool connects directly to the vehicle diagnostic port. Once it's hooked up, the tool can communicate via the can bus like any other module.
If the instrument cluster does not respond, the reason why must be determined. Like any other electrical device, the instrument cluster must have an intact circuit, complete with power and ground. The circuit can be tested using a DMM.
At this point, all signs point to a faulty instrument cluster. However, before condemning the cluster, its software should be checked. In some cases, reprogramming the cluster fixes the problem. If not, the instrument cluster will need to be replaced. Some clusters require programming after replacement.
All the 'U' codes are network communication codes. Codes U0100 to U0300 are lost communication with XX module codes.
On many vehicles, battery voltage must be between 9 - 16 volts for code U0155 to set.
