What this code means
U0100 can be stored when the body control module cannot receive specified data from the PCM.
What the vehicle may do
- The body control module may not receive specified PCM data.
- U0100 may be stored if the PCM does not start normally.
Possible fault areas
- A PCM power/ground circuit failure may be involved.
- An open F-CAN circuit between the CAN gateway and PCM is possible.
- A PCM problem may be involved.
Diagnostic path
Understanding U0100
On this 2025 Honda Accord 1.5, U0100 means the body control module has lost communication with the PCM. When the body control module cannot receive the specified PCM data, it stores this code. Possible fault areas include the PCM power/ground circuit, the communication wiring, and the PCM itself. Here is what this code tells us. The body control module may not receive specified PCM data. U0100 may be stored if the PCM does not start normally. Here are the main areas to check. A PCM power/ground circuit failure may be involved. An open F-CAN circuit between the CAN gateway and PCM is possible. A PCM problem may be involved.
U0100-specific prerequisites
Before you troubleshoot U0100, review How to Troubleshoot. If you are troubleshooting multiple DTCs, follow the steps in B-CAN System Diagnosis Test Mode A. U0100 may be stored if the PCM does not start normally. It may also be stored because of a PCM power/ground circuit failure. Before this troubleshooting, check the PCM power/ground circuit first. Then use the troubleshooting for F-CAN Lost Communication (CAN BUS with Connection to CAN Gateway). Let us go through those shared communication checks.
The code identifies missing PCM data at the body control module, not the reason that data is missing. A PCM that does not start normally or has a power/ground circuit failure can also lead to this code. That is why the PCM power/ground check comes before the shared F-CAN lost-communication troubleshooting, rather than treating U0100 alone as evidence of a wiring fault or a faulty PCM.
Before the shared communication checks
Before you troubleshoot, review How to Troubleshoot. If the failure comes and goes or is difficult to reproduce, review How to Troubleshoot (Handling Intermittent and Low Reproducibility Failures). Use the diagnostic scanner (HDS) result from Communication Status Check of F-CAN Connected Units. Check the power/ground circuit of the transmitting control unit that shows NG. These shared checks address lost communication on the F-CAN circuit connected to the CAN gateway.
Find the unit showing NG
Troubleshoot any DTCs listed or indicated systems below first. Network Communications \[CAN gateway\]: Go to the indicated DTC's troubleshooting
First, troubleshoot any indicated Network Communications \[CAN gateway\] DTCs using the troubleshooting for the indicated code. Then run Communication Status Check of F-CAN Connected Units with the scanner. Use the control unit showing NG to choose the following checks. For details on using this scanner function, review How to Troubleshoot (Handling Ongoing Failures).
The NG result selects which control unit's diagnostic branch applies; it is not itself the PCM diagnosis. When the PCM shows NG, its power/ground circuit check and the applicable open-wire inspections distinguish the circuit path from the PCM path.
Shared confirmation routine
The shared confirmation routine is defined separately: turn the vehicle to the ON mode. For its details, check the Confirmation Procedure for the DTC being diagnosed. For this episode, that is U0100; its confirmation routine is explained later.
Separate open-wire checks
The listed scanner function is CAN Gateway ＞ Function Test ＞ Communication Status Check of F-CAN Connected Units. Separately, the physical open-wire routine checks the wiring between the CAN gateway and PCM. Before you disconnect the PCM connector, jump the SCS line with the scanner. Wait more than 1 minute before disconnecting it. The following open-wire checks apply if the PCM shows NG in Communication Status Check of F-CAN Connected Units.
PF-CAN A_H wire check
For these wire checks, IG Mode must be OFF. CAN gateway connector A (24P) and PCM connector A (72P) must be disconnected, with the SCS-line precaution already satisfied. Use the female terminals. First, check PF-CAN A_H. Place one probe on CAN gateway connector A terminal 6. Place the other probe on PCM connector A terminal 69. The reading should be less than 1 ohm. A reading below that limit is normal for this wire check.
PF-CAN A_L wire check
For the PF-CAN A_L check, IG Mode must be OFF. CAN gateway connector A (24P) and PCM connector A (72P) must be disconnected. Use the female terminals. Place one probe on CAN gateway connector A terminal 18. Place the other probe on PCM connector A terminal 55. The reading should be less than 1 ohm. A reading below that limit is normal for this wire check.
PD-CAN B_H wire check
For the PD-CAN B_H check, IG Mode must be OFF. CAN gateway connector A (24P) and PCM connector A (72P) must be disconnected. Use the female terminals. Place one probe on CAN gateway connector A terminal 23. Place the other probe on PCM connector A terminal 72. The reading should be less than 1 ohm. A reading below that limit is normal for this wire check.
PD-CAN B_L and the results
For the PD-CAN B_L check, IG Mode must be OFF. CAN gateway connector A (24P) and PCM connector A (72P) must be disconnected. Use the female terminals. Place one probe on CAN gateway connector A terminal 11. Place the other probe on PCM connector A terminal 71. The reading should be less than 1 ohm. A reading below that limit is normal for this wire check. If any of these open-wire checks gives an abnormal result, there is a problem in the circuit. If the results are normal, this diagnostic branch points to a problem with the PCM.
The PCM conclusion depends on the set of four open-wire results, not a passing reading on only one wire. Each check has a normal limit of less than 1 ohm. Within this PCM-NG branch, an abnormal result identifies a circuit problem; normal results across the four checks point to a PCM problem.
U0100 confirmation routine
The separate U0100 confirmation routine has two actions. Turn the vehicle to the ON mode. Then wait for at least 6 seconds.
Listed scanner function
Another listed scanner function reference is Body Electrical ＞ Lighting ＞ Data List.
Final check
Possible fault areas include PCM power/ground, the F-CAN wiring between the CAN gateway and PCM, and the PCM.
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