What this code means
U0155 may indicate that the SRS unit is not communicating normally with the gauge control module.
What the vehicle may do
- Warning indicators may behave unexpectedly.
- The fault may be intermittent or present only under certain conditions.
- Scan tool communication may show a network-related fault.
Possible fault areas
- Possible network communication issue.
- Possible connector or terminal condition.
- Possible wiring issue between modules.
- Possible module communication concern.
Diagnostic path
Open with what U0155 means
On this 2010 to 2015 Honda Civic with the 1.8 gas engine, U0155 means the SRS unit has lost communication with the gauge control module. In plain terms, one module is expecting to talk to the instrument cluster side of the network and it may not be getting the message back. The driver may see warning indicators behave incorrectly, and the fault can involve network communication, connector condition, module communication, or wiring between the SRS unit and the gauge control module. Before you get deep into the circuit testing, treat this like an SRS job: find out whether the vehicle has been in a collision, confirm any required collision-related components were the correct new parts and installed properly, and follow the normal SRS and battery-disconnect precautions.
Start with network context
Start with the basic system checks using the HDS. Check the body electrical system for any F-CAN or B-CAN communication faults. If other communication codes are present, do not chase U0155 in isolation. Check what those communication faults mean first, because they can change the direction of the diagnosis. If there are no other communication faults, move on to the indicator check.
Use the brake indicator as the next gate
Release the parking brake, turn the ignition switch to ON (II), and watch the brake system indicator. The expected behavior is that it comes on for 2 seconds and then goes off. If it does that, continue with the code confirmation step. If it does not come on and then go off after 2 seconds, run the gauge control module self-diagnostic function. If that self-check shows a gauge control module problem, replace the gauge control module tach, clear the code, and retest. If U0155 is still present after that path, replace the SRS unit.
Confirm the code before circuit testing
Now confirm the fault. Clear the DTCs with the HDS, turn the ignition switch to ON (II), wait for 10 seconds, and check for codes again with the HDS. If U0155-00 comes right back, go to the F-CAN wire checks. If U0155-00 does not return, treat it as an intermittent failure and the system is OK at that moment. If a different code shows up instead, follow that code rather than forcing this diagnostic path.
Check the F-CAN high and low circuits for an open
For the open-wire check, turn the ignition switch to LOCK (0). Disconnect the negative battery cable and wait at least 3 minutes. Then disconnect SRS unit connector A, the 39P connector, and disconnect the gauge control module tach 32P connector. With those connectors disconnected, check continuity on both network lines. For F CAN-H, check between SRS unit connector A 39P terminal No. 20 and gauge control module tach 32P terminal No. 19, the white wire. For F CAN-L, check between SRS unit connector A 39P terminal No. 21 and gauge control module tach 32P terminal No. 20, the red wire.
Make the decision from the continuity result
If both lines have continuity, the F CAN-H and F CAN-L wires are considered OK in this check. At that point, focus on the SRS unit connection at connector A and the SRS unit itself. Before replacing the SRS unit, check the SRS unit software version with the HDS. If it is not the latest version, update the SRS unit software and retest. If the connection is OK and the diagnostic path still points there, replace the SRS unit. If the code still does not clear after that, replace the dashboard wire harness. If either CAN line does not have continuity, the path is an open in the harness between the SRS unit connector A terminals and the gauge control module tach connector terminals that were just tested. In that case, replace the dashboard wire harness, then clear the DTC.
Verify separately and close
After the repair path is completed, keep verification separate from the testing steps. Clear the DTC, retest under the same basic conditions, and confirm U0155 stays gone. The takeaway is simple: prove the network is not being pulled off course by other communication faults, confirm the cluster-side indicator behavior, then test the F-CAN high and low paths between the SRS unit and the gauge control module before condemning a module or harness. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code is often approached by checking related communication faults first, confirming the fault returns, and then testing the communication wiring before making a module or harness decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
