What this code means
P1658 may mean the PCM is detecting an electronic throttle control relay circuit problem when the relay should be on.
What the vehicle may do
- The check engine light may be on.
- Throttle response may feel reduced or limited.
- The vehicle may enter a protective strategy depending on how the fault is detected.
Possible fault areas
- Possible ETCS control relay issue.
- Possible poor connection or loose terminal at the relay or PCM.
- Possible shorted relay control or relay output wiring.
- Possible PCM software or PCM control concern.
Diagnostic path
Open and frame the fault
On this Accord, P1658 is an ETCS control relay ON malfunction. In plain terms, the PCM may be seeing a problem in the electronic throttle control relay circuit when that relay should be operating. The driver may notice a warning light, reduced throttle response, or the car may feel limited, depending on how the fault shows up. The possible fault areas here are the ETCS control relay, poor terminals or connections, a shorted relay control or output circuit, and in some cases PCM software or PCM control. Before getting deep into testing, save the freeze data and any on-board snapshot, then start with the basic system checks so you know whether this is current or intermittent.
Verify the problem with the ETCS test
Start by turning the ignition switch to ON (II), or selecting ON mode with the engine start/stop button. With the HDS, run the ETCS test and watch whether the relay circuit checks out. If the relay circuit is OK, treat it as an intermittent failure at this point. The system is OK right now, so concentrate on poor connections or loose terminals at the ETCS control relay and the PCM. If the relay circuit is not OK, the failure is duplicated, and the next move is to test the relay itself.
Test the ETCS control relay
Turn the ignition switch to LOCK (0), or select OFF mode. Remove the ETCS control relay from the under-hood fuse and relay box, then test the relay. If the relay fails the test, replace the ETCS control relay and move to repair verification. If the relay tests OK, leave the relay circuit diagnosis in play and go after the wiring side next.
Check the relay control line for a short to ground
With the ignition still in LOCK (0), or OFF mode, jump the SCS line with the HDS. Disconnect PCM connector A, the 51P connector. With the ETCS control relay disconnected and PCM connector A disconnected, check continuity on the DBW RLY CL- circuit between PCM connector A, terminal No. 19, the WHT wire, and body ground. If there is continuity, repair the short in the DBW RLY CL- wire between PCM A19 and the ETCS control relay, then verify the repair. If there is no continuity, that control wire is OK, so continue to the output side of the relay circuit.
Check the relay output circuit for a short to power
Next, disconnect PCM connector C, also a 51P connector. Turn the ignition switch to ON (II), or select ON mode. With the ETCS control relay disconnected, PCM connector A disconnected, and PCM connector C disconnected, measure voltage on the VBDBW circuit between PCM connector C, terminal No. 2, the YEL/GRN wire, and body ground. If battery voltage is present, repair the short to power in the DBW RLY OUT/VBDBW wire between PCM C2 and the ETCS control relay, then verify the repair. If battery voltage is not present, that wire is OK. At that point, update the PCM if it does not have the latest software, or substitute a known-good PCM, then go to repair verification.
Verify the repair and confirm the code stays gone
For repair verification, turn the ignition switch to LOCK (0), or select OFF mode. Reconnect all connectors, exit SCS mode with the HDS, then turn the ignition switch to ON (II), or select ON mode. Reset the PCM with the HDS, do the PCM idle learn procedure, and check for Pending or Confirmed DTCs with the HDS. If P1658 is still indicated, go back to the ETCS control relay and PCM connections and check for poor connections or loose terminals. If the PCM was updated, substitute a known-good PCM and recheck. If the PCM was substituted, return to the beginning of the P1658 diagnostic path. If P1658 is not indicated, troubleshooting is complete. If a substituted PCM fixed the issue, replace the original PCM. If other Pending or Confirmed codes are present, check what they mean first instead of treating them as part of this P1658 path.
Takeaway and CTA
The key with P1658 is to prove the relay circuit response before condemning anything. Verify the fault with the HDS, test the relay, check the control side for a short to ground, check the output side for a short to power, and only then move toward PCM software or a known-good PCM check. For more diagnostic training, visit stepdiagnostics.com.
Final check
This fault is often best approached by confirming the relay command response first, then separating relay failure from wiring faults and PCM-related possibilities.
For more guided automotive diagnostics, visit STEP Diagnostics.
