Dealing with my daughters car and I'm up against a wall here. First I admit I'm not "Acura" guy, just a pretty good home mechanic that enjoys this stuff. My daughters car is a 2012 Acura TL SH-AWD with the 3.7l J37A4 engine code. She ran it low on oil (begged her to keep an eye) and ruined engine. I didn't want to rebuild that 3.7 or invest in another J37A4 so after researching I found that the J35Z6 is a direct swap. So i overhauled a J35Z6 engine and installed it. Everyhting is great except I get no VTEC engagement. At 5500 RPMs the engine stutters like its hitting a rev limiter and the CEL comes on with a P2646 code ROCKER ARM OIL CONTROL VALVE (A) STUCK ON/OFF. I have had the spool valve off and the screen and all passages are clear. Also new OEM sensor and solenoid. I feel as though i have exhausted all mechanical reasons for the code except a possible blocked oil passage in the front head? The rear head was off this engine and planed and cleaned and some valves replaced, so i have to believe that head is good.
So my question becomes is it ECU related? Does the computer look for a certain oil pressure that the 3.7 creates and the 3.5 maybe doesn't create enough so it isn't engaging the solenoid? If I'm not mistaken the 3.7 liter engine had VTEC on both the intake and exhaust cams but the 3.5 only runs VTEC on the intake cam. Does the 3.5 generate less oil pressure due to only needing to activate intake VTEC and the computer doesn't like it? Any help or suggestions would be greatly appreciated.

 

DTC P2646: Rocker Arm Oil Pressure Switch Circuit Low Voltage

Special Tools Required

• Pressure Gauge Adapter 07NAJ-P07010A
• A/T Low Pressure Gauge w/Panel 07406-0070301
• AT Pressure Test Hose 07AAJ-PY4A100
• A/T Pressure Adapter 07MAJ-PY40120
• Oil Pressure Hose 07ZAJ-S5AA200

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information.

1. Check the engine oil level.Is the engine oil level OK?
   
   YES - Go to step 2.
   
   NO - Adjust the engine oil to the proper level, then go to step 19.
   
2. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
3. Clear the DTC with the HDS.
4. Do the VTEC TEST in the INSPECTION MENU with the HDS.Is the result OK?
   
   YES - Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the rocker arm oil pressure switch, the rocker arm oil control solenoid, and the ECM/PCM. ■
   
   NO - Go to step 5.
   
5. Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.
6. Disconnect the rocker arm oil pressure switch 2P connector.
7. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
8. Check the VTEC PRES SW in the DATA LIST with the HDS.Is switch ON indicated?
   
   YES - Go to step 14.
   
   NO - Go to step 9.
   
9. Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.
10. Remove the rocker arm oil pressure switch (A), attach the special tools as shown in illustration below, then attach the rocker arm oil pressure switch to the oil pressure gauge adapter (B).
    Fig 1: Installing Special Switch And Rocker Arm Oil Pressure Switch With Torque Specifications
    Courtesy of AMERICAN HONDA MOTOR CO., INC.
11. Start the engine.
12. Do the VTEC TEST in the INSPECTION MENU with the HDS.
13. Check the oil pressure.Does the oil pressure increase to at least 392 kPa (4.0 kgf/cm 2 , 56.9 psi)?
    
    YES - Replace the rocker arm oil pressure switch, then go to step 18.
    
    NO - Inspect the VTEC system. If it is OK, replace the rocker arm oil solenoid, then go to step 18.
    
14. Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.
15. Jump the SCS line with the HDS.
16. Disconnect ECM/PCM connector B (49P).
17. Check for continuity between ECM/PCM connector terminal B20 and body ground.
    Fig 2: Checking Continuity Between ECM/PCM Connector Terminal B20 And Body Ground
    Courtesy of AMERICAN HONDA MOTOR CO., INC.Is there continuity?
    
    YES - Repair short in the wire between the ECM/PCM (B20) and the rocker arm oil pressure switch, then go to step 18.
    
    NO - Go to step 24.
    
18. Reconnect all connectors.
19. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.
20. Reset the ECM/PCM with the HDS.
21. Do the ECM/PCM idle learn procedure (see ECM/PCM IDLE LEARN PROCEDURE).
22. Do the VTEC TEST in the INSPECTION MENU with the HDS.
23. Check for Pending or Confirmed DTCs with the HDS.Is DTC P2646 indicated?
    
    YES - Check for poor connections or loose terminals at the rocker arm oil pressure switch, the rocker arm oil control solenoid, and the ECM/PCM, then go to step 1.
    
    NO - Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting. ■
    
24. Reconnect all connectors.
25. Update the ECM/PCM if it does not have the latest software (see ECM/PCM UPDATE), or substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM).
26. Do the VTEC TEST in the INSPECTION MENU with the HDS.
27. Check for Pending or Confirmed DTCs with the HDS.Is DTC P2646 indicated?
    
    YES - Check for poor connections or loose terminals at the rocker arm oil pressure switch, the rocker arm oil control solenoid, and the ECM/PCM. If the ECM/PCM was updated, substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM), then go to step 26. If the ECM/PCM was substituted, go to step 1.
    
    NO - If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM (see ECM/PCM REPLACEMENT). If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.
    

This is all I could find regarding P2646, maybe there is something there that could help?

 

Well, I found out what it was and fixed it very easily. When I did the engine swap, I put a new solenoid and a new sensor for the VVT system on the car. The parts were labeled as OEM and they were in what looked like factory Honda packaging when I purchased them from an eBay seller. While having a diagnostic session with a Chatbot, I showed a picture of the packaging from the auction for the items I bought and the Chatbot suggested that although they were packaged as OEM there’s still a possibility that they were not and that their specs may be throwing the system off. So in my scrap pile I found the old VVT sensor and took the new one out of the car and put the old one on and it totally fixed the problem. Engine runs like perfect now.

 

That'll do it..


STOP BEING OEM PARTS ON EBAY OR AMAZON.


They're complete trash and 90% chance they're counterfeit too.