What this code means
U0029 may mean the VSA control unit is seeing a CAN network communication problem where messages can become unreliable or stop being accepted normally.
What the vehicle may do
- The vehicle may show stability, traction, ABS, or brake-related warning indicators.
- Driver-assist or stability functions may be limited while the communication fault is active.
- The fault can be intermittent, especially if the condition depends on vibration, connector fit, or operating state.
Possible fault areas
- Possible CAN wiring or connector issues between the PCM and VSA modulator-control unit.
- Possible loose terminals or poor connections at the VSA modulator-control unit connector.
- Possible VSA modulator-control unit software concern.
- Possible VSA modulator-control unit fault after wiring, connector, and software checks are completed.
Diagnostic path
Opening context and setup
On this Accord, U0029 is a CAN communication failure, bus off, seen by the VSA control unit. In plain language, the VSA side may be losing reliable communication on the CAN network. The driver may see stability, traction, ABS, or brake-related warning behavior, and the possible fault areas can include the network wiring between the PCM and VSA modulator-control unit, connector terminal condition, module software, or the VSA modulator-control unit itself. Before chasing this code, start with the basic system checks and follow a structured diagnostic approach. If any PGM-FI codes are present, handle those first, because engine control communication faults can steer this diagnosis the wrong way.
Verify the failure first
Start by verifying the problem. Turn the vehicle to the ON mode, clear the DTC with the HDS, then turn the vehicle to the OFF (LOCK) mode and start the engine. Wait 2 seconds or more, then check for DTCs again with the HDS. If U0029-00 comes back, the failure is duplicated and you move into the network wiring check. If U0029-00 does not come back, treat it as an intermittent failure. The system is OK at this time, so try to reproduce the captured conditions if freeze data or an on-board snapshot was recorded.
Check the F-CAN wiring for an open
With the failure duplicated, check the F-CAN_H and F-CAN_L lines for an open between the VSA modulator-control unit and the PCM. Turn the vehicle to the OFF (LOCK) mode. Jump the SCS line with the HDS and wait more than 1 minute. Then disconnect the VSA modulator-control unit 38P connector and PCM connector A (51P). On the 2.4 L4, check continuity from VSA connector No. 38 to PCM connector A (51P) No. 2, and from VSA connector No. 26 to PCM connector A (51P) No. 1. If there is continuity, the F-CAN_H and F-CAN_L wires are OK, so continue to the VSA modulator-control unit check. If there is no continuity, repair the open in the wire between the PCM and the VSA modulator-control unit.
Update and recheck the VSA modulator-control unit
Next, reconnect the VSA modulator-control unit 38P connector and PCM connector A (51P). Update the VSA modulator-control unit if it does not have the latest software. Then turn the vehicle to the OFF (LOCK) mode, start the engine, wait 2 seconds or more, and check for DTCs with the HDS. If U0029-00 is still indicated, check for loose terminals and poor connections at the VSA modulator-control unit 38P connector. If the VSA modulator-control unit was updated and the symptom or indication is still present, replace the VSA modulator-control unit. If U0029-00 is not indicated, this troubleshooting path is complete. If other codes are present, check what those codes mean first.
Takeaway
The key is not to condemn the VSA unit too early. Verify the code, prove the CAN wiring between the PCM and VSA unit, then handle software, connector fit, and final confirmation in order. For more diagnostic training, visit stepdiagnostics.com.
Final check
U0029 often needs a step-by-step network check: confirm the code, test the communication lines, then verify software and connector condition before making a final call.
For more guided automotive diagnostics, visit STEP Diagnostics.
