What this code means
P0848 may mean the transmission control system is seeing the transmission fluid pressure switch B, for the 3rd clutch, stuck high or not changing as expected.
What the vehicle may do
- The vehicle may set a warning light.
- The transmission may shift abnormally or feel harsh at times.
- The vehicle may also appear to drive normally if the concern is intermittent.
Possible fault areas
- Possible pressure switch signal concern.
- Possible wiring, connector, or terminal issue between the pressure switch and the PCM.
- Possible PCM software or PCM input concern.
Diagnostic path
Opening context
On this Civic, P0848 is pointing at the transmission fluid pressure switch B circuit for the 3rd clutch reading high. In plain language, the computer may not be seeing the 3rd clutch pressure switch signal change the way it expects. The vehicle may have shift complaints, may set the light, or may feel normal if the fault is intermittent. The broad areas to keep in mind are the 3rd clutch pressure switch, the OP_3_SW signal wire between the switch and the PCM, connector or terminal condition, and possible PCM software or PCM input concerns. We are going to keep the testing in order and prove the signal path before calling the repair.
Before testing
Before clearing anything, capture the stored scan-tool data and any onboard snapshot with the HDS. That gives you the conditions the car saw when the code set, and it keeps you from chasing a fault blind after the memory is cleared.
Check the 3rd pressure switch signal
Start with the live signal check. Turn the ignition switch to ON (II), clear the code with the HDS, then set the vehicle up so the drive wheels can rotate safely. Block the rear wheels and raise the front of the vehicle, or use a lift. Make sure it is securely supported. Warm the engine to normal operating temperature, when the radiator fan comes on. Disable VSA with the VSA OFF button, run the vehicle in 3rd gear, and watch the 3rd Pressure Switch in the A/T Data List. If the switch shows ON in 3rd gear, the signal is acting correctly at that moment, so move to duplicating the failure. If it does not show ON, go straight to the circuit and switch checks.
Duplicate the failure
Next, try to make the fault happen under the required drive condition. Test-drive the vehicle in 3rd gear for at least 2 seconds, and monitor the OBD STATUS for P0848 in the HDS DTC menu. If the status shows FAILED, the fault is duplicated and you continue into the electrical checks. If it shows PASSED, treat it as an intermittent fault for now and inspect for poor connections or loose terminals between transmission fluid pressure switch B and the PCM. If the status is NOT COMPLETED, run the drive condition again instead of jumping ahead.
Check voltage at the pressure switch connector
For the pressure switch check, 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). Measure voltage on the OP_3_SW circuit between terminal No. 1, the BLK/RED wire, and body ground. With that connector disconnected and the ignition ON (II), you are looking for about 5 V. If about 5 V is present, the procedure calls for replacing transmission fluid pressure switch B, then moving to repair verification. If about 5 V is not present, continue to the open-wire check.
Check the OP_3_SW wire for an open
Now check the signal wire itself. Turn the ignition switch to LOCK (0), jump the SCS line with the HDS, and disconnect PCM connector B, the 49P connector. With the pressure switch connector still disconnected and PCM connector B disconnected, check continuity on the OP_3_SW line between the pressure switch B connector No. 1, BLK/RED, and PCM connector B No. 9, BLK/RED. If there is continuity, the OP_3_SW 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 there is no continuity, repair the open in the OP_3_SW wire between the pressure switch and the PCM, then verify the repair.
Verify the repair
Keep verification separate from the testing. Reconnect all connectors, turn the ignition switch to ON (II), and clear the code with the HDS. Start the engine and warm it to normal operating temperature, when the radiator fan comes on. Test-drive in 3rd gear for at least 2 seconds, then drive in 4th gear for at least 2 seconds, and monitor the OBD STATUS for P0848. If it shows PASSED, the P0848 troubleshooting is complete. If a known-good PCM was substituted, replace the original PCM. After that, check for any other pending or confirmed codes and diagnose those separately. If the status shows FAILED, go back to the beginning of this diagnostic path and recheck; if the PCM was updated, substitute a known-good PCM and check the OBD STATUS again. If it shows NOT COMPLETED, meet the test condition and check the OBD STATUS again.
Closing takeaway
The key with P0848 is not to guess at the transmission. Prove whether the 3rd clutch pressure switch signal turns on in 3rd gear, then verify the 5-volt feed and the OP_3_SW wire back to the PCM. Once the repair path is complete, run the OBD status check and make sure the code stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0848 can often be diagnosed by confirming the live switch signal, reproducing the fault condition, checking the switch circuit voltage, checking continuity back to the PCM, and then verifying the OBD
For more guided automotive diagnostics, visit STEP Diagnostics.
