What this code means
P0873 may indicate that the ECM/PCM is seeing a high signal from the transmission fluid pressure switch C circuit for the 4th clutch.
What the vehicle may do
- The transmission may enter a fail-safe strategy and limit shifting.
- The driver may notice abnormal shift behavior or limited gear availability.
Possible fault areas
- Possible pressure switch circuit concern
- Possible transmission fluid pressure switch C concern
- Possible wiring, connector, or terminal concern between the switch and PCM
- Possible PCM concern after circuit checks support that direction
Diagnostic path
Opening context
On this 2010 through 2017 Honda Accord with the 2.4 gas engine, P0873 is tied to the transmission fluid pressure switch C circuit for the 4th clutch. In plain terms, the ECM/PCM is seeing that pressure-switch signal high when it is checking that circuit. The vehicle may go into fail-safe shifting, and on this code the transmission does not shift to any gear other than 1st or 4th gear. Broadly, this can involve the switch circuit, the switch itself, wiring or terminal problems between the switch and PCM, or in the final branch, the PCM. Start with the basic system checks before getting into the pinpoint path.
Verify the problem first
Begin with problem verification. Turn the vehicle to ON mode, then clear the DTC with the HDS. Raise the vehicle on a lift, make sure it is securely supported, and make sure all four wheels can rotate freely. Start the engine, then disable VSA with the VSA OFF button. If vehicle speed will be above 31 mph (50 km/h), enter VSA maintenance mode. Now run the vehicle in 4th gear and watch the 4th Pressure Switch parameter on the HDS. The threshold being checked here is ON. After the check, slow down and stop the wheels.
Decide whether the failure is active
If the 4th Pressure Switch condition matches the ON threshold while it is in 4th gear, treat it as an intermittent failure; the system is OK at that moment. Check closely for poor connections and loose terminals between the 4th clutch pressure switch and the PCM. If captured data was stored with this DTC, try to reproduce the same conditions. If the condition does not match the threshold in 4th gear, the failure is duplicated, so continue into the circuit check.
Check whether the switch side can pull the signal correctly
Turn the vehicle to OFF, then disconnect the transmission fluid pressure switch C, 4th clutch, 1P connector. Install a jumper between the switch connector No. 1 terminal, the BLU wire, and body ground. Turn the vehicle back to ON mode and check the 4th Pressure Switch parameter with the HDS again. The threshold is still ON. If the current condition matches the threshold, replace transmission fluid pressure switch C, 4th clutch. If it does not match the threshold, move on to the OP4SW wire check.
Check the OP4SW wire for an open
For the open-wire check, turn the vehicle OFF, remove the jumper wire, jump the SCS line with the HDS, and disconnect PCM connector B, the 51P connector. With the vehicle OFF, the pressure switch C 1P connector disconnected, and PCM connector B disconnected, check continuity on the OP4SW circuit between the pressure switch connector No. 1 BLU wire and PCM connector B, terminal No. 26, also BLU. If there is continuity, the OP4SW wire is OK, and the next call is to replace the PCM. If there is no continuity, repair the open in the OP4SW wire between transmission fluid pressure switch C and the PCM.
Takeaway
The key on P0873 is to separate an intermittent switch signal from a duplicated failure, then prove whether the grounded switch circuit can report correctly before condemning the wire or PCM. Keep the final confirmation separate from the pinpoint testing, and make sure the code stays gone under the same operating conditions. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code is often approached by verifying the switch signal first, then checking whether the OP4SW circuit between the switch and PCM is intact.
For more guided automotive diagnostics, visit STEP Diagnostics.
