What this code means
U0029 can indicate that the CAN gateway cannot receive signals via PF-CAN A.
What the vehicle may do
- The CAN gateway can store U0029 when PF-CAN A signals are missing.
Possible fault areas
- Possible faults include the external PF-CAN A circuit.
- A connected PCM or TCM may have an internal short.
- The CAN gateway itself may be at fault.
Diagnostic path
Understanding U0029
On this 2025 Honda Accord 1.5, U0029 means CAN Gateway F-CAN ch A Bus Off. The CAN gateway stores this code when it cannot receive signals via PF-CAN A. Possible fault areas include the external circuit, connected units, and the gateway itself. Here is what this code tells us. The CAN gateway can store U0029 when PF-CAN A signals are missing. Here are the main areas to check. Possible faults include the external PF-CAN A circuit. A connected PCM or TCM may have an internal short. The CAN gateway itself may be at fault.
The code describes what the gateway detected—missing PF-CAN A signals—not which part caused it. That distinction is why the diagnostic path separates the external circuit, connected units, and gateway. The gateway conclusion depends on normal results from the other inspection items, rather than on U0029 alone.
Shared resistance-check method
First, let us explain the separate resistance-check method used for short-to-ground checks. This defines the method, rather than starting the U0029 checks now. Use the specific inspection points and measurement conditions for the check being made. Disconnect the connector on every component that belongs to the circuit being checked. Measure resistance between the connector terminal being checked and body ground. The normal reading is more than 1 MΩ, meaning no continuity.
Checking other ground lines
The next measurement in that resistance-check method is within the same connector. Measure resistance between the terminal being checked and the other GND lines in that connector. The normal reading is more than 1 MΩ, meaning no continuity.
Separate voltage-check method
There is also a separate voltage-check method for a circuit expected to have battery or reference voltage. This method can check for a short to body ground. Voltage checks should cover different vehicle modes, including ON, OFF, and ACC. To use this method, disconnect the connector of the component receiving the power supply or reference voltage. To measure voltage, place one probe on that connector's power-supply or reference-voltage terminal and the other on body ground. The normal reading is the power supply or reference voltage.
Before troubleshooting U0029
Before you troubleshoot, review How to Troubleshoot. U0029 may be stored at the same time as an OTA error code. If both are stored together, clear the OTA error code after clearing the DTC. Both clearing actions must happen in the same driving cycle, meaning the same IG mode ON cycle.
Confirmation Procedure
The separate Confirmation Procedure is this: turn the vehicle to the ON mode, and wait 6 seconds.
Checking between the two circuit wires
Let us explain the separate PF-CAN A_H, PF-CAN A_L Shorted Wire Inspection. Before disconnecting the PCM connector and the TCM connector, jump the SCS line with the diagnostic scanner (HDS). Wait more than 1 minute before disconnecting those connectors. Prepare with CAN gateway connector A (24P), PCM connector A (72P), and TCM connector (50P) disconnected. For the wire-to-wire measurement, IG Mode must be OFF. At the disconnected CAN gateway connector A (24P), place one probe on female terminal 6 and the other on female terminal 18. Measure resistance. The normal reading is more than 1 megohm.
Checking PF-CAN A_H to ground
For the following short-circuit checks, use the Open/Shorted Wire Inspection Description method explained earlier. Apply the method that fits the circumstances. Keep CAN gateway connector A (24P) disconnected, with IG Mode OFF. To check PF-CAN A_H, place one probe on female terminal 6 and the other on ground. The normal reading is more than 1 megohm.
Checking PF-CAN A_L to ground
For the PF-CAN A_L check, keep CAN gateway connector A (24P) disconnected, with IG Mode OFF. Place one probe on female terminal 18 and the other on ground. The normal reading is more than 1 megohm. If any of these external-circuit checks is abnormal, there is a problem in the circuit.
These measurements check different short-circuit paths: between PF-CAN A_H and PF-CAN A_L, and from each wire to ground. A normal wire-to-wire result does not establish that either wire's ground check is normal. With the specified connectors disconnected and IG Mode OFF, each external-circuit measurement has its own requirement of more than 1 MΩ; an abnormal result identifies a circuit problem.
Checking connected units
The PF-CAN A Bus Connected Unit Check is a separate procedure. Its normal starting condition is that the external circuit is normal. This check can also be done before the other inspections are completed because it includes all the following inspection items. If it fails, each inspection item must then be checked individually to find which item failed. Before disconnecting the PCM connector and the TCM connector, jump the SCS line with the scanner. Wait more than 1 minute before disconnecting those connectors. Prepare with CAN gateway connector A (24P), PCM connector A (72P), and TCM connector (50P) disconnected. Reconnect PCM connector A (72P), then TCM connector (50P), one by one. Inspect after each reconnection. For each inspection, keep CAN gateway connector A (24P) disconnected, with IG Mode OFF. Measure between female terminals 6 and 18. The expected result is not shorted.
The option to run this procedure early does not remove the external-circuit condition needed to interpret a connected-unit fault. If the early check fails, the individual inspection items must separate the possible faults. A failed early check is therefore not, by itself, enough to assign the short to a connected unit.
Connected-unit terminal 6 check
As part of the checks after each one-by-one reconnection, measure female terminal 6 to ground. CAN gateway connector A (24P) must remain disconnected for this measurement, with IG Mode OFF. The expected result is not shorted.
Connected-unit terminal 18 check
Also check female terminal 18 to ground after each one-by-one reconnection. CAN gateway connector A (24P) must remain disconnected for this measurement, with IG Mode OFF. The expected result is not shorted. If a connected-unit inspection is abnormal, the unit whose connector is connected has a shorted circuit.
The one-by-one reconnections tie each set of results to the unit being connected. Each set covers all three paths, not just the two wires measured together. With the external circuit normal, CAN gateway connector A (24P) still disconnected, and IG Mode OFF, an abnormal connected-unit inspection identifies a shorted circuit in the unit whose connector is connected.
CAN gateway conclusion
The separate CAN Gateway Inspection depends on the results of the other checks. If all the other inspection items are normal, the remaining CAN gateway is the cause. Under that condition, there is a problem with the CAN gateway.
Final check
Possible fault areas include the external circuit, a connected unit, or the CAN gateway, depending on the inspection results.
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