What this code means
P0847 may indicate the PCM is seeing a low signal on the transmission fluid pressure switch B, or 3rd clutch pressure switch, circuit.
What the vehicle may do
- The vehicle may set a warning light.
- The transmission may shift differently under certain conditions.
- The code may appear only when the correct drive conditions are met.
Possible fault areas
- Possible 3rd clutch pressure switch signal issue.
- Possible switch circuit or connector issue.
- Possible wiring issue between the pressure switch and the PCM.
- Possible PCM software or control-side issue.
Diagnostic path
Opening context
On this 2010 to 2015 Honda Civic with the 1.8 gas engine, P0847 is for the transmission fluid pressure switch B, the 3rd clutch pressure switch, circuit low. In plain language, the PCM may be seeing that switch signal pulled low when it should not be. The vehicle may have shift complaints, a warning light, or it may only show the code during the right drive conditions. The broad fault areas can include the 3rd clutch pressure switch signal, the switch circuit, wiring to the PCM, or PCM software and control. The key point on this one: treat P0847 as an electrical circuit problem, not a mechanical transmission failure. Before testing, record the freeze data and any on-board snapshot with the HDS so you know the conditions the code was captured under.
Initial signal check and problem verification
Start with the signal check. Turn the ignition switch to ON (II), clear the DTC with the HDS, then look at the 3rd Pressure Switch in the A/T Data List while the transmission is not in 3rd gear. The question is whether the 3rd Pressure Switch reads OFF. If it does read OFF, move on and try to duplicate the fault. If it does not read OFF, the signal is considered OK at that point, and the next move is still to check the switch and circuit directly. To verify the problem, start the engine and warm it up to normal operating temperature, meaning the radiator fan comes on. Then test-drive the vehicle in 4th gear for at least 2 seconds, and monitor the OBD STATUS for P0847 in the HDS DTCs menu. If the HDS shows FAILED, the failure is duplicated, so continue with the switch check. If it shows PASSED, treat it as an intermittent condition for now; the system is OK at this time, and you are looking for an intermittent short to ground in the wire between the transmission fluid pressure switch B and the PCM. If it shows NOT COMPLETED, the monitor did not finish, so test-drive again under the required conditions.
Check the 3rd clutch pressure switch
Next, check transmission fluid pressure switch B, the 3rd clutch switch. Turn the ignition switch to LOCK (0), disconnect the transmission fluid pressure switch B 1P connector, then turn the ignition switch back to ON (II). With the connector disconnected, check the 3rd Pressure Switch on the HDS in the A/T Data List. If the 3rd Pressure Switch reads OFF, replace transmission fluid pressure switch B, then go to repair verification. If it does not read OFF, the switch itself is considered OK, and the diagnosis moves to the OP_3_SW circuit.
Check the OP_3_SW wire for a short to ground
For the short-to-ground check, turn the ignition switch to LOCK (0), jump the SCS line with the HDS, and disconnect PCM connector B, the 49P connector. Keep the transmission fluid pressure switch B 1P connector disconnected. With the ignition in LOCK (0), check for continuity on the OP_3_SW circuit between transmission fluid pressure switch B connector terminal No. 1, the BLK/RED wire, and body ground. If there is continuity, repair the short to ground in the OP_3_SW wire between the switch and the PCM, then verify the repair. If there is no continuity, the OP_3_SW wire is considered OK. At that point, update the PCM if it does not have the latest software, or substitute a known-good PCM, then move to repair verification.
Verify the repair
Keep verification separate from the testing. Reconnect all connectors, turn the ignition switch to ON (II), and clear the DTC with the HDS. Start the engine, warm it up until the radiator fan comes on, then test-drive in 3rd gear for at least 2 seconds, followed by 4th gear for at least 2 seconds. Monitor the OBD STATUS for P0847 in the HDS DTCs menu. If the status shows PASSED, troubleshooting is complete. If a known-good PCM was substituted and the test passes, replace the original PCM. After that, check for other DTCs; if any are present, follow that code’s diagnostic path. If the status shows FAILED, go back to the first signal check and recheck the path. If the PCM had been updated, substitute a known-good PCM and check OBD STATUS again. If the status shows NOT COMPLETED, meet the test condition and check OBD STATUS again.
Closing takeaway
The takeaway for P0847 is to prove the switch signal first, duplicate the code when possible, isolate the switch from the OP_3_SW wire, and only move toward PCM software or substitution after the switch and short-to-ground checks are handled. Keep it electrical, verify the monitor, and confirm the code stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0847 is best approached as an electrical signal diagnosis: confirm the switch state, duplicate the fault when possible, check the circuit for a short to ground, and verify the code stays gone.
For more guided automotive diagnostics, visit STEP Diagnostics.
