What this code means
P16F3 may indicate that the ECM/PCM is seeing low voltage on the starter cut relay 1 control circuit.
What the vehicle may do
- The vehicle may start normally with an intermittent code.
- The vehicle may set the code again after clearing.
- The vehicle may have a no-start condition.
Possible fault areas
- Possible wiring faults in the starter cut relay control circuit.
- Possible poor connections or loose terminals at the relay circuit board or PCM.
- Possible relay circuit board, ignition feed, fuse, or under-dash fuse/relay box involvement.
- Possible PCM software or PCM control concern.
Diagnostic path
Set up the diagnosis
On this Accord, P16F3 points to a low-voltage problem on the ECM/PCM starter cut relay 1 control circuit. In plain terms, the PCM is not seeing that starter cut control circuit behave the way it should. The car may still start, it may have an intermittent fault, or it may come in as a no-start. The broad fault areas can include the starter cut control wire, relay circuit board connections, the ignition feed side, the under-dash fuse and fuse box area, or PCM software and PCM control. Before testing, save the captured data and on-board snapshot, then start with the basic system checks so you know whether this is a hard fault or something intermittent.
Start with whether the engine starts
First, try to start the engine. If the engine starts, treat this as a code verification path and go straight into duplicating P16F3. If the engine does not start, skip ahead to checking the starter system input with the scan tool.
If it starts, verify whether P16F3 comes back
With an engine that starts, turn the vehicle OFF, then turn it back ON. Clear the code with the HDS, then check for pending or confirmed codes. If P16F3 comes right back, the failure is duplicated and you can test the ST CUT RLY1 CL- circuit for a short to ground. If P16F3 does not return, call it intermittent for now. The system is OK at this moment, so concentrate on poor connections or loose terminals at the relay circuit board and the PCM.
Check the ST CUT RLY1 CL- line for a short
For a duplicated code on a vehicle that starts, turn the vehicle OFF, jump the SCS line with the HDS, then disconnect relay circuit board connector A, the 8P connector, and PCM connector A, the 51P connector. Check continuity on the ST CUT RLY1 CL- line between PCM connector A, terminal No. 33, green wire, and body ground. If there is continuity, repair the short in the ST CUT RLY1 CL- wire between PCM A33 and the relay circuit board, then verify the repair. If there is no continuity, 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 verify the repair.
If it does not start, check the starter cut return signal
If the engine did not start at the first check, turn the vehicle ON. On an automatic, put the shifter in P or N. On a manual, put it in neutral and press the clutch pedal. Watch the STARTER CUT CTRL RETURN parameter with the HDS. The expected threshold is ON. If the current condition matches that threshold, keep going in this P16F3 circuit path. If it does not match, leave this path and diagnose the engine-will-not-start symptom.
Separate PCM-side control from circuit-side faults
Next, turn the vehicle OFF, jump the SCS line with the HDS, disconnect PCM connector A, then turn the vehicle back ON. Again, use P or N on an automatic, or neutral with the clutch pressed on a manual. Measure voltage on the ST CUT RLY1 CL- circuit between PCM connector A, terminal No. 33, green wire, and body ground. If battery voltage is present, update the PCM if needed, or substitute a known-good PCM, then verify the repair. If battery voltage is not present, move down the circuit and test from the relay circuit board side.
Check for an open in the ST CUT RLY1 CL- line
With PCM connector A still disconnected and the vehicle ON, measure voltage on the ST CUT RLY1 CL- circuit at relay circuit board connector A, terminal No. 5, green wire, to body ground. If battery voltage is present there, the IG1 ACG feed is OK, and the problem is an open in the ST CUT RLY1 CL- wire between PCM A33 and the relay circuit board. Repair that open, then verify the repair. If battery voltage is not present, keep moving upstream to the IG1 ACG side.
Check the IG1 ACG feed at the relay circuit board
Now measure the IG1 ACG circuit at relay circuit board connector A, terminal No. 4, pink wire, to body ground, with the vehicle ON and PCM connector A disconnected. If battery voltage is present, replace the relay circuit board, then verify the repair. If battery voltage is not present, check the fuse feeding this part of the circuit.
Check the under-dash fuse
Turn the vehicle OFF and check the No. B13 (15 A) fuse in the under-dash fuse/relay box. If the fuse is OK, continue with the IG1 ACG open-circuit check. If the fuse is not OK, replace the No. B13 (15 A) fuse, turn the vehicle ON, then back OFF. If the fuse blows again, repair the fault to body ground on the No. B13 (15 A) fuse circuit, then verify the repair.
Check the IG1 ACG wire for an open
For the IG1 ACG open check, disconnect relay circuit board connector A and the under-dash fuse/relay box F connector. The F connector is the 18P connector for the applicable USA, Mexico, or Canada layout. Jumper terminal No. 11, pink wire, at that under-dash fuse/relay box connector to body ground. Then check continuity from relay circuit board connector A, terminal No. 4, pink wire, to body ground. If there is continuity, the IG1 ACG wire is OK, so replace the under-dash fuse/relay box for the applicable market, then verify the repair. If there is no continuity, repair the open in the IG1 ACG wire between the under-dash fuse/relay box and the relay circuit board, then verify the repair.
Verify the repair and confirm the code stays gone
Keep verification separate from the circuit tests. Turn the vehicle OFF, reconnect every connector, exit SCS mode with the HDS, then turn the vehicle ON. Reset the PCM with the HDS, do the PCM idle learn procedure, and check pending and confirmed codes again. If P16F3 is still indicated, recheck for poor connections or loose terminals at the relay circuit board and PCM. If the PCM was updated, substitute a known-good PCM and recheck. If a PCM was already substituted, go back to the beginning of the diagnostic path. If P16F3 is not indicated, the result depends on what was done: if the PCM was updated, the troubleshooting is complete; if a known-good PCM fixed it, replace the original PCM. If other codes are present, check what they mean first.
Takeaway
The clean way through P16F3 is to prove whether the starter cut control circuit is shorted, open, missing its feed, or being driven incorrectly before condemning a module. Follow the voltage and continuity results in order, then verify the repair and make sure the code stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
Diagnose P16F3 by following the circuit path in order, separating wiring and feed problems from relay board, fuse box, and PCM-side possibilities.
For more guided automotive diagnostics, visit STEP Diagnostics.
