The check engine light came on. Scoped it and the engine code P2647 came up. Changed the oil pressure switch and cleaned the screen. Check engine light came on again. Scoped it again and engine code P2646 showed up, so the entire solenoid was replaced. Check engine light came on again with same P2646 plus P0661. P0661 was a code that came up a year ago whereby the intake manifold solenoid was replaced. Now I'm unable to clear it.

I took it to a mechanic who said that I have a buildup of sludge and the only way to remedy this was to rebuild/clean the engine. I religiously change my oil every 3000 miles so I was shocked at this diagnosis and that those that change my oil would not see this buildup. He warned against cleaners...and offered to buy my car cheap.

Can anyone validate this claim that my engine requires a rebuild?

Does anyone have any additional thoughts related to my issues?

Looking for remedies.

  • Welcome to the site! We're glad you've stopped by :o) You may want to change your question to ask how to remove engine sludge or some such. Asking it the way you did is asking for product endorsement and can be construed as a "shopping question", mainly because you are looking for a product, not a solution. Jul 1, 2016 at 19:25
  • I'm confused the P0661 has nothing to do with engine sludge and either the Intake Manifold Tuning valve is unplugged or the wiring is damaged. Given that you can't clear the code/it sets right away. As to the P2646 did they confirm oil pressure at the switch? I'd suggest getting a second opinion.
    – Ben
    Jul 1, 2016 at 19:32
  • You're right that P0661 has nothing to do with sludge but always seems to come up when there is a problem elsewhere. Nothing was confirmed. The initial code, prior to changing the switch was P2647 - after the replacing the switch the code changed to P2646, so I replaced the entire solenoid.
    – user19472
    Jul 1, 2016 at 20:01
  • 1
    I'd tee in a oil pressure gauge and compare against spec at 4000 rpm before having anymore parts replaced. I think the 2646 code is for voltage high/pressure low make sure the return signal to the ecm is ok as well.
    – Ben
    Jul 1, 2016 at 21:20
  • 1
    Update - The code P0661 apparently had to do with the newly replaced oil pressure valve solenoid assembly - having to be reset - it is now cleared. P2646 continues to be an issue but has been temporarily cleared when screen in new solenoid was cleaned. Apparently there is sludge that continues to clog these screens.
    – user19472
    Jul 8, 2016 at 21:41

5 Answers 5


I found TSB:49031-02409 Version 3 MIL Comes ON with DTC P2646/P2651 or P2647/P2652


The MIL comes on with one of these DTCs:

^ P2646/P2651 (rocker arm oil pressure switch circuit low voltage).

^ P2647/P2652 (rocker arm oil pressure switch circuit high voltage).

NOTE: The symptom may be intermittent and you may not be able to duplicate it after clearing the DTC.


The rocker arm oil pressure switch 37250 PNE G01 may fail intermittently.


Replace the rocker arm oil pressure switch.

Not to be confused with the the sender unit 37240P2FA01


Hmmm. It could be that sludge has built up.. if I were you I'd do several engine flush and see if the drained oil looks sticky or dark.


Rebuild? Not enough information to say, so don't consider it yet.

But your engine can certainly have sludge accumulation in parts you'll never see (without tearing it down) even when you religiously follow the manufacturer's OCI. And if you're not the first/original owner, you should expect the prior owners did not follow the OCI. All that to say, it's entirely probable you have at least some sludge, and using a reputable engine cleaner -- not an oil additive -- won't hurt.

  • Thank you. I bought the car with 60k miles on it. It now has 160k miles. I used Sea Foam a couple of times. Car is throwing another error code now, P0325 in addition to the standard P0661 and P2646
    – user19472
    Jun 26, 2017 at 18:40
  • I've used Sea Foam, but not lately. I prefer Auto-RX. Just my 2¢.
    – Mac
    Jun 27, 2017 at 0:13
  • That P0325 is the knock sensor circuit going south on you. If you replace the sensor, and the code returns, and if you're sure the wiring is good and the pin on the ECM is good, then consider an ECM software update or a replacement ECM, in that order.
    – Mac
    Jun 27, 2017 at 0:39

I, too, have had sludge problems on relatively new cars. Change oil & filter with Mobil 1 FS and substitute one quart with Marvel Mystery Oil. Immediately drive car at highway speeds for as long as possible.

Repeat changing oil and using Marvel Mystery Oil every 500 miles until the sludge is gone. It may require 3,000 miles of usage in cases of heavy sludge buildup, but it always works without damaging the engine.


As noted in a previous answer, the engine can build sludge via different routes overtime. Some places in the engine have areas where the flow of oil is slow or minimal, deposits can build in these areas causing sludge (sludge is nothing more than oil and dropout particles). OTC engine cleaners for sludge buildup are expensive. I have been doing the following for about 30+ years now.

You will need the following items depending on how dirty the engine is, in your case I would recommend no less than two shots of this treatment. 2-3 quarts of ATF - automatic transmission fluid. ATF has a very high level of detergent in a very light oil, both do a great job of cutting the sludge down and removing it. An oil change, including filter for your vehicle with the correct oil viscosity. On a normal V-8 I normally use 1 1/2 quarts of ATF. Then drive the car normally for several days to a week. Drain oil, remove filter and be warned that you will not believe how dirty your oil is going to look. Replace with your normal oil change. Again on your vehicle, I would repeat this process a second time and then see if you can clear your code.

Assuming that this takes care of it, change out this oil and filter at no more than 500 miles. Internally your engine should be relatively clean at this point. The other code related to the intake gasket sounds like a vacuum leak that you will have to find. And last point, if anyone is having hydraulic valve lifter noise, most likely a sticking lifter plunger, this cleaning routine will normally take care of that problem too.

  • In my day trani fluid was used all the time - today you're considered crazy. The latest Error Code reading includes P2646, P0661 - which seems to be the standard on this car, plus the newest addition, P0325. My check engine light stays on 75% of the time, but will go off on occasion. The car doesn't seem to run any different whereas before, the VSA would be tripped and cause the car to choke at certain speeds. At this point, I can't even sell the car and trading it in will be an insult. So much of this car has been changed as Ive spent a ton of money replacing parts.
    – user19472
    Jun 26, 2017 at 18:37

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