What this code means
P0990 may indicate that the PCM is seeing a high circuit condition from transmission fluid pressure switch E, also described as the 6th clutch pressure switch.
What the vehicle may do
- The vehicle may enter a fail-safe strategy.
- Shifting can be limited when this code is stored.
- The technician may need to reproduce the concern while monitoring scan-tool data.
Possible fault areas
- A possible pressure switch concern.
- Possible connector or terminal problems between the switch and PCM.
- A possible open in the OP6SW signal wire.
- A possible PCM-side concern after the circuit checks correctly.
Diagnostic path
Opening context
On this Accord, P0990 points to a high circuit condition for transmission fluid pressure switch E, the 6th clutch pressure switch. In plain terms, the PCM may be seeing the 6th clutch pressure switch signal in a state it does not expect. The car may go into a fail-safe strategy, and with this code stored, shifting can be limited so the transmission does not use gears other than 3rd or 6th. Before getting deep into testing, start with the basic system checks. Think in broad terms first: this may be a pressure switch issue, a connector or terminal issue, an open in the OP6SW signal wire, or, after the circuit checks out, a possible PCM-side problem.
Problem verification
Start by verifying the problem before condemning anything. Turn the vehicle to the ON mode, clear the DTC with the HDS, then raise the vehicle on a lift. Make sure it is securely supported, and make sure all four wheels can rotate freely. Start the engine, disable VSA with the VSA OFF button, then run the vehicle in 6th gear and watch the 6th Pressure Switch parameter on the HDS. Slow the vehicle down and stop the wheels when the check is done. The threshold you are comparing against here is 6th Pressure Switch ON. If vehicle speed is above 31 mph (50 km/h), enter VSA maintenance mode.
Interpreting the first check
If the current condition matches the threshold in 6th gear, treat it as an intermittent failure for now. The system is OK at this time, so look closely for poor connections and loose terminals between the 6th clutch pressure switch and the PCM. If captured data is available for this DTC, try to reproduce the failure under the same captured conditions. If the condition does not match the threshold, the failure is duplicated, so move into the circuit isolation test.
Isolating the switch from the rest of the circuit
Next, turn the vehicle to the OFF, LOCK, mode. Disconnect the transmission fluid pressure switch E, 6th clutch, 1P connector. Connect terminal A to terminal B with a jumper wire. Terminal A is the pressure switch 1P connector number 1, gray wire. Terminal B is body ground. Then turn the vehicle back to the ON mode and check the 6th Pressure Switch parameter with the HDS. Again, the threshold shown for the decision is 6th Pressure Switch ON.
Interpreting the jumper check
If the current condition matches the threshold during that jumper check, replace transmission fluid pressure switch E, the 6th clutch pressure switch. If it does not match the threshold, do not stop at the switch. Continue with the OP6SW wire continuity check.
Checking the OP6SW wire for an open
For the open-wire check, turn the vehicle back to the OFF, LOCK, mode and remove the jumper wire. Jump the SCS line with the HDS, then disconnect PCM connector B, the 51P connector. Now check continuity on the OP6SW circuit between the transmission fluid pressure switch E, 6th clutch, 1P connector number 1, gray wire, and PCM connector B, 51P, terminal number 28, gray wire. The test condition is vehicle OFF, LOCK, mode, the pressure switch connector disconnected, and PCM connector B disconnected.
Interpreting the continuity check
If continuity is present, the OP6SW wire is OK, and the diagnostic path calls for PCM replacement. If continuity is not present, repair the open in the OP6SW wire between transmission fluid pressure switch E, 6th clutch, and the PCM.
Verification and takeaway
Keep the logic clean: first confirm whether the fault is present in 6th gear, then use the jumper check to separate a switch problem from the rest of the circuit, and finally prove the OP6SW wire before making the PCM call. After the correction, verify the repair by returning to the same operating check and confirming the code stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
Confirm the fault under the proper operating condition, isolate the switch from the circuit, then prove the OP6SW wire before making the final call.
For more guided automotive diagnostics, visit STEP Diagnostics.
