P0325 refuses to die . . .

(Tried posting this on a different Honda forum, got one reply TLR - not exactly helpful. Hoping for better here.)

Car is an 01 Accord, LX with about 125K on it. It is my grocery getter. Bought it from an estate in 2003 with 22K on it from a little old lady who didn't drive it much - but she bumped into things. (I know this because I was the executor of her estate).

Properly maintained since, regular oil changes, filters, brake pads, (several window winders), new motor mounts, new radiator and hoses, new PS pump, A/C repaired (compressor failed), VTEC solenoid replaced (leaked), distributor seal replaced (AutoZone said I needed a new distributor, $500, it was a 50 cent seal which I changed myself), new plugs and wires, everything written down. Clear coat failed, the car looks like it has leprosy, that can wait.

Car laid down a smokescreen like a WW2 destroyer - big clouds of white smoke. Everyone said head gasket but nobody (including me) thought to do a compression test. Head gasket changed ($800 later), more white smoke, turned out to be the warmup regulator on the back of the head. Kinda hard to get to, now I know the inspiration for the Kama Sutra. He also changed the throttle body, the old one was sticking off idle.

Replaced warmup regulator, the car wasn't driven between the time the head was reinstalled and the regulator was replaced - that's important.

CEL came on, P0325 knock sensor. Mechanic has now replaced the knock sensor FOUR times to no avail. I finally convinced him that the sensor (all four of them) is telling the truth, there IS something wrong, and it isn't a defective sensor. ("Oil pressure gauge shows zero, we can't be out of oil, it must be the gauge." Nope.) He does it because he has a lift - access is easier that way, I'm too old and too smart to crawl under cars any more.

Replaced the wire between the firewall plug and the knock sensor, no change, light still comes on. Clear the code, light still comes on. (He replaced the wire, I'm not sure how good he is with electrical work.)

Checked that the timing belt marks are correct - they are. (When I had the belt changed at about 80K, it was one tooth off, the CEL promptly came on. Corrected the belt, cleared code, light stayed off.)

I doubt the ECU has failed, this problem only arose immediately after the head gasket was changed.

It runs quite well, but is getting something like 10 mpg, so I really think it needs to be fixed. (Then I promise I'll paint it - honest.)

I am now out of altitude, airspeed and ideas. I don't want to take it to an authorized Honda dealer because I don't want to get a second mortgage. I absolutely can fix this myself but I absolutely don't know what I am looking for at this point. All the "usual suspects" are accounted for - unless I'm missing something.

Ideas? Exorcist? Bonfire? Sell it to Elon and let him send it to Mars? (And have the Martians attack us in revenge?) I can't even tear my hair out in frustration because I am already bald.

Best Regards,
Mike/Florida

 

Is this a V6 or 2.3L 4-cylinder engine?

 

It is the 2.3 engine, inline four. (Thank you!)

 

Not sure what you mean by warmup regulator? I'm guessing the fast idle valve or the idle air control valve was leaking? Not important for your current issue, but I'm curious about what happened.

The knock sensor is a one wire circuit, so pretty simple. What is the color of the wire going to the knock sensor? What brand and part number are they using on your car?

I thought accords only had the low oil pressure light and not a pressure gauge. What gauge in your cluster is not working?

 

The "warmup regulator" (probably incorrect terminology) is on the back of the cylinder head. It gets coolant on one side and intake air on the other. The original failure was the gasket, it let coolant into the inlet manifold, hence the white smoke which everyone "knew" indicated a blown head gasket.

(That's the problem with "everyone knows". I had a 280SE Mercedes some years ago with air suspension, it would sit with the rocker panels on the ground after a few hours. "Everyone" said it was the $900 pump, which I knew wasn't correct because if you ran the car for two minutes, it would lift right up to normal height. Turned out to be a pinhole leak in one air line.)

I will have to go look at the color code. I didn't do the wiring (which I probably should have) and I will advise.

We've had four sensors so far - the original one, which "coincidentally" went bad when the head was reinstalled, another OEM one from the parts yard the throttle body came from, and two more aftermarket from eBay. My feeling is the two original sensors were fine, the two aftermarket ones could be, and the wire from the sensor to the firewall plug was replaced, but at this point I am a bit reluctant to swear to the guy's competence, so I need to look at it Only remaining sensor is in the car, he discarded the others.

There's no gauge, there is only a light (which isn't complaining). The comment about the gauge not being bad is from aviation - if the attitude indicator says you are inverted, you probably are, the gauge isn't lying no matter how much you might want it to be. That's what I finally convinced the mechanic of - the knock sensor IS telling the truth, there IS something wrong, and it isn't the sensor. Four bad sensors in a row isn't probable, and the problem arose immediately after the head was re-installed, so we need to look there. (Who is the last guy who worked on this and what did he do?)

<<Back from watching the Crew Dragon return>>

I think what I ought to do next is check that he got the timing belt on correctly, then check the color code and connections (signal and shield). After I cleared the code, it was fine for about four miles, and then bingo, check engine is back on. The car runs quite well, but it just isn't right yet.

Best Regards,
Mike/Florida

 

The oil pressure swtich and the knock sensors are both one-wire sensors. I believe the sensors are close by, so it could be possible that the original insaller accidentally swapped the connectors. I'm not 100% sure the wire connectors are the same, but it is possible.

The knock sensor should have a red/blu wire and the oil pressure switch a yel/red wire connected to it.

 

Now that's interesting . . . (but it is 9PM here and I can't go look right now).

I wonder what would show in the gauge cluster if that were the case. (I'm going to go look, but you've got my curiosity up.)

Stay tuned - there are two possibilities here, 1) Aha, that's it, car is fixed, and 2) Nope, that isn't it, keep looking.

Best Regards,
Mike/Florida