What this code means
P100A may indicate that the ECM or PCM is detecting an electric VTC motor circuit malfunction.
What the vehicle may do
- The vehicle may illuminate a warning light.
- The vehicle may have cam timing control-related symptoms.
- The vehicle may have little or no noticeable driveability complaint.
Possible fault areas
- Possible electric VTC motor circuit issue.
- Possible power, ground, control wiring, or connector issue.
- Possible electric VTC motor issue.
- Possible PCM issue after other checks indicate normal.
Diagnostic path
Open and frame the fault
On this Accord Hybrid, P100A points to an ECM or PCM fault detection in the electric VTC motor circuit. In plain language, the controller is not seeing the electric VTC motor feedback behave the way it expects. The vehicle may show a warning light, may have cam timing control complaints, or may not have an obvious driveability symptom. The broad fault areas can include the electric VTC motor circuit, its power feed, its ground and control wiring, connector condition, the motor itself, or, after the other checks pass, the PCM. The code sets when the EVTM line output is out of the expected range while the electric VTC relay is being commanded on.
Start with confirmation
Start with the basic system checks and follow a structured diagnostic approach before going into circuit testing. Turn the vehicle to ON mode, then run the HDS IN-VTC test. If that test is not OK, treat the failure as duplicated and move into the circuit checks instead of guessing at parts.
Check the VB1 EVTC feed
Next, prepare for the VB1 EVTC circuit inspection by disconnecting the 6-pin electric VTC motor connector. With that connector disconnected and IG Mode ON, check the VB1 EVTC feed at the specified connector test points. A normal result is 12 V battery voltage. If that check is abnormal, the fault is in the circuit. If the power supply portion of that check is abnormal, continue with the additional power supply inspection to narrow down the failure location.
Prepare for PCM-side circuit checks
Before disconnecting the PCM connector, jump the SCS line with the HDS and wait more than 1 minute. Then disconnect the 6-pin electric VTC motor connector and PCM connector B, the 101-pin connector. This is one of those steps where connector handling matters, so do not skip the SCS wait before unplugging the PCM connector.
Check opens in the control and ground circuits
With the electric VTC motor connector and PCM connector B disconnected, and IG Mode OFF, check the EVTP, EVTM, and EVTC_GND circuits for opens. Each of those open-wire checks should be less than 1 Ω. If any of them are abnormal, the problem is in that circuit. The terminal-specific test-point details are not available here, so pause and confirm the correct connector pin locations before measuring. Do not backfill the missing pin information from memory.
Check shorts to ground
After the open checks, inspect for shorts to ground according to the short-circuit inspection method. With IG Mode OFF, check EVTP shorted to ground and EVTM shorted to ground. A normal result for each is more than 1 MΩ. If either result is abnormal, stay on that circuit fault path rather than moving on to the motor or PCM.
Use a known-good motor only after circuit checks
For the electric VTC motor inspection, there is no direct test method listed for that item, so the diagnostic path uses a known-good electric VTC motor. Install the known-good motor and try to reproduce the failure. If the failure is still reproduced, the fault is with other related components. If the symptom or DTC goes away with the known-good motor, the electric VTC motor is the failed item.
PCM conclusion and final check
Only after the other inspection items have shown normal results does the path call the remaining PCM the cause. Keep that as the end of the decision tree, not the starting point. After the fault path is corrected, verify the result by confirming the failure does not reproduce and P100A stays gone. The takeaway: confirm the code, prove the power feed, prove the wiring for opens and shorts, use the known-good motor only where the path calls for it, and leave PCM judgment until the circuit and motor checks have passed. For more diagnostic training, visit stepdiagnostics.com.
Final check
P100A is often approached as a circuit-first diagnosis: confirm the fault, test the feed and wiring, then evaluate the motor and PCM only after those checks support it.
For more guided automotive diagnostics, visit STEP Diagnostics.
