What this code means
P1659 may mean the PCM is seeing an electronic throttle control relay response that does not match what it expects.
What the vehicle may do
- The vehicle may set a warning light.
- Throttle response may feel limited or abnormal.
- The condition can be intermittent if relay or PCM terminals have poor contact.
Possible fault areas
- Possible ETCS control relay concern.
- Possible fuse, power feed, or relay box concern.
- Possible open or short in drive-by-wire relay wiring.
- Possible loose or poor connection at the relay or PCM.
- PCM software or PCM internal concerns may be considered after circuit checks.
Diagnostic path
Opening and setup
On this Accord, P1659 points to the electronic throttle control relay circuit not behaving the way the PCM expects. In the bay, that may show up as reduced throttle response, a warning light, or other electronic throttle symptoms. The possible fault areas to keep in mind are the ETCS control relay, its power feed and control wiring, the under-hood fuse and relay box, connector condition at the relay and PCM, and in some cases PCM software or PCM substitution for testing after the circuit checks are done. Before chasing it, record the freeze data and any on-board snapshot, then start with the basic system checks so you know whether this is current or intermittent.
Confirm the code first
Start by turning the ignition switch to ON (II), or selecting ON mode with the engine start/stop button. Clear the code with the HDS, then check for Pending or Confirmed DTCs. If P1659 comes right back, the failure is duplicated and you move into circuit testing. If it does not come back, treat it as intermittent for now. At that point, the system is OK at this time, so concentrate on poor connections or loose terminals at the ETCS control relay and the PCM.
Check the fuse and relay path
With the ignition in LOCK (0), check fuse No. A18 (15 A) in the under-hood fuse and relay box. If that fuse is OK, continue to the ETCS control relay. Remove the relay from the under-hood fuse and relay box and test the relay. If the relay tests good, keep going with the socket voltage checks. If the relay does not test good, replace the ETCS control relay, then verify the repair. The relay test needs a defined test method and pass-fail criteria; if you do not have that information available at the bench, pause and do not guess on the relay result.
Check relay socket power feeds
Next, turn the ignition back to ON (II), or ON mode, with the ETCS control relay still disconnected. Measure voltage on the FI MAIN RLY OUT circuit between ETCS control relay 4P socket No. 3 and body ground. If you have battery voltage there, move to the +B DBW feed. If you do not have battery voltage, replace the under-hood fuse and relay box, then verify the repair. For the +B DBW check, measure between ETCS control relay 4P socket No. 1 and body ground. If battery voltage is present, that feed is OK and you continue to the PCM-side continuity checks. If battery voltage is missing, repair an open in the +B DBW wire between the No. A18 (15 A) fuse and the ETCS control relay, or replace the under-hood fuse and relay box, then verify the repair.
Check for opens between the relay and PCM
Now shut the ignition to LOCK (0), or OFF mode. Jump the SCS line with the HDS, disconnect PCM connector C (51P), and check continuity on the DBW RLY OUT/VBDBW circuit between ETCS control relay 4P socket No. 2 and PCM connector C (51P) No. 2, the YEL/GRN wire. If there is continuity, that wire is OK. If there is no continuity, repair the open between PCM C2 and the ETCS control relay, then verify the repair. After that, disconnect PCM connector A (51P) and check the DBW RLY CL- circuit between ETCS control relay 4P socket No. 4 and PCM connector A (51P) No. 19, the WHT wire. If there is no continuity, repair the open between PCM A19 and the ETCS control relay, then verify the repair. If continuity is good there, the relay control wiring has passed this part of the path, so update the PCM if it does not have the latest software, or substitute a known-good PCM, then verify the repair.
If the fuse was not OK, check for shorts
If fuse No. A18 (15 A) was not OK, follow the short-check path. Remove the ETCS control relay, jump the SCS line with the HDS, disconnect PCM connector C (51P), and check continuity from PCM connector C (51P) No. 2, the YEL/GRN wire, to body ground on the VBDBW circuit. If there is continuity, repair the short in the DBW RLY OUT/VBDBW wire between PCM C2 and the ETCS control relay, then verify the repair. If there is no continuity, that wire is OK, so check the +B DBW circuit between ETCS control relay 4P socket No. 1 and body ground. If there is continuity there, repair the short in the +B DBW wire between the No. A18 (15 A) fuse and the ETCS control relay, or replace the under-hood fuse and relay box, then verify the repair. If there is no continuity, the +B DBW wire is OK, so update the PCM if it does not have the latest software, or substitute a known-good PCM, then verify the repair.
Verify the repair
Keep verification separate from the circuit tests. Turn the ignition to LOCK (0), or OFF mode, reconnect all connectors, exit SCS mode with the HDS, then turn the ignition to ON (II), or ON mode. Reset the PCM with the HDS, do the PCM idle learn procedure, and check again for Pending or Confirmed DTCs. If P1659 is still indicated, recheck for poor connections or loose terminals at the ETCS control relay and the PCM. If the PCM was updated, substitute a known-good PCM and recheck. If the PCM had already been substituted, go back to the problem verification step and start the diagnostic path again. If P1659 is not indicated, troubleshooting is complete. If a PCM was substituted, replace the original PCM. If other codes are present, check what they mean first and follow the correct diagnostic path for those. The takeaway is simple: prove the relay power supply, prove the relay output and control wiring, then handle PCM software or substitution only after the circuit path checks out. For more diagnostic training, visit stepdiagnostics.com.
Final check
This diagnosis often comes down to proving the relay power, output, and control circuits before moving toward PCM-level decisions.
For more guided automotive diagnostics, visit STEP Diagnostics.
