What this code means
P0847 may indicate the PCM is seeing a low signal from the transmission fluid pressure switch B, commonly described as the 3rd clutch pressure switch circuit.
What the vehicle may do
- The vehicle may enter a fail-safe shift strategy.
- Shift operation can feel limited or abnormal while the code is active.
Possible fault areas
- Possible pressure switch circuit issue
- Possible pressure switch or connector issue
- Possible wiring or terminal issue between the switch and PCM
- Possible PCM-side circuit concern after other checks are proven
Diagnostic path
Opening context
On this 2010 through 2017 Honda Accord with the 2.4 gas engine, P0847 points to a low-circuit condition for transmission fluid pressure switch B, the 3rd clutch pressure switch. In plain terms, the PCM may be seeing the 3rd clutch pressure switch signal lower than expected. The vehicle may go into a limited fail-safe shift pattern, and the possible fault areas are the pressure switch circuit, the switch itself, connector or terminal condition, the OP3SW signal wire, or, only after the circuit checks prove out, the PCM side of the circuit. Before getting deep into testing, record the freeze data and any on-board snapshot with the HDS, then start with the basic system checks and follow a structured diagnostic approach.
Important direction before testing
One key point on this code: this diagnostic path treats P0847 as an electrical circuit problem, not a mechanical transmission problem. Also know that if P0847 is stored in the PCM, the fail-safe function keeps the transmission from shifting to any gear other than 3rd or 6th gear. So do not chase hydraulic or internal mechanical causes first; stay focused on the switch signal circuit until the electrical checks tell you otherwise.
Step 1 — duplicate the fault
Start by verifying the problem. Select ON mode with the engine start/stop button, clear the DTC with the HDS, and watch the 3rd Pressure Switch parameter. The expected threshold for this first check is ON. If the current condition matches that threshold, the failure is duplicated, so continue to the next test. If it does not match, treat it as an intermittent failure. At that point the system is OK at this time, and the next move is to inspect for poor connections and loose terminals between the 3rd clutch transmission fluid pressure switch and the PCM.
Step 2 — separate the switch from the rest of the circuit
If the fault is duplicated, turn the vehicle OFF, disconnect the transmission fluid pressure switch B, the 3rd clutch switch connector, then turn the vehicle back ON. Now check the 3rd Pressure Switch parameter again with the HDS. For this check, the expected threshold is OFF. If the current condition matches that threshold with the switch disconnected, the diagnostic result points to replacing transmission fluid pressure switch B, the 3rd clutch pressure switch. If the condition does not match, keep going into the wiring check.
Step 3 — check the OP3SW wire for a short to ground
For the next check, turn the vehicle OFF, jump the SCS line with the HDS, and disconnect PCM connector B, the 51P connector. With the transmission fluid pressure switch B 1P connector still disconnected and PCM connector B 51P disconnected, check continuity on the OP3SW circuit between PCM connector B 51P No. 25, the light blue wire, and body ground. If there is continuity, repair the short to body ground in the OP3SW wire between transmission fluid pressure switch B and the PCM. If there is no continuity, the OP3SW wire is OK, and the diagnostic result is to replace the PCM.
Wrap-up
Keep the verification separate from the testing path, and do not skip ahead. The takeaway is simple: prove whether the switch signal changes correctly, then check the OP3SW wire for a short to ground before condemning the control side. For more diagnostic training, visit stepdiagnostics.com.
Final check
This diagnosis should stay focused on the electrical switch signal path before considering anything beyond the circuit.
For more guided automotive diagnostics, visit STEP Diagnostics.
