Pre-Road Trip Inspection (P0740, P0420, P0430, and oil leak)

[csprinkle]

Hey all,

 

Thinking of doing a road trip from WA down the coast to Cali sometime and I wanted to make sure my pathy is in good enough condition to confidently do so. It's my commuter/daily so I know it can get me to work and back fine but there still are three pending codes that it likes to throw, as well as a check engine light. Here they are: P0740 Starter Signal Circuit/Torque Converter Clutch Solenoid, P0420 Catalyst System Bank 1, and P0430 Catalyst System Bank 2. In the past, I've had a P0304 misfire but I solved that with a new spark plug/ignition coil. Also, I am by no means anything more than a socket and wrench mechanic. I have an OBDII Innova 5210 Handheld scanner that I can use for at-home testing, but I'm not sure where to start.

 

For P0740, is that worth getting diagnosed at a shop? I don't mind shelling out a bit of money to get that one fixed by a professional since I'm not too keen on tinkering with my transmission. I did a quick search on the 96-2004 R50 forums and found minimal information on a fix; maybe I just wasn't looking for the right keywords. My gears seem to change fine, first to second is always rough but there's never any gears that get stuck and I've never experienced a stall.

 

For the two cat codes, P0420 and P0430, are those even worth looking at? Or rather, if I don't pay any attention to them now will that come back to bite me? I'd like to get that fixed if its bogging down my power, since I feel like I'm driving a tank sometimes when I go up a hill at anything sub 2500 rpm. Maybe I just drive slow.

 

And lastly, I have a decent oil leak issue. I would assume the valve cover gasket is in shambles, but I'd prefer to have that one done at a shop as well. I've attached a photo that shows what I think is oil running down the underbelly towards the front of the vehicle - someone more knowledgeable would probably be able to diagnose where the leak is coming from. The oil pan seems to have a bit of the leak but majority of the leakage doesn't seem to be below the oil pan when I check. Again, should I just let that one be and keep refilling with synthetic 5W-30? Kinda sucks to leave a footprint everywhere I park.

 

Some extra info:

• SE 2002 4wd auto
• mileage: 277,000 miles
• combined avg mpg: 17.5
• slight vibration in chassis and steering wheel when idle, gets worse when highway speeds

 

If you are able to answer even one question that I've asked in this post, that would mean a ton to me. Really trying to figure out what's going on with my pathy so I don't let it get in worse condition. Thank you!

 

Edited August 8 by csprinkle
forgot to include that i had a check engine light

[hawairish]

Howdy.

 

If you're not familiar with the Factory Service Manual, they can be extremely helpful: https://www.nicoclub.com/nissan-service-manuals.  Recommend to download each PDF for your model year (there's a download link below the inset PDF viewer).  The General Information (GI) is a great starting point for how to read diagrams, wire colors, harnesses, etc.

 

You'll want the Automatic Transmission (AT) chapter for the P0740: https://www.nicoclub.com/service-manual?fsm=Pathfinder%2F2002%2Fat.pdf

You'll want the Engine Control (EC) chapter for the others: https://www.nicoclub.com/service-manual?fsm=Pathfinder%2F2002%2Fec.pdf

 

For the P0740, ignore the "Starter Signal Circuit" part of what your code scanner is giving.  The code is for the torque converter clutch signal.  You won't notice anything different for gears 1-3, as this applies to the transmission being able to lock up the torque converter while in 4th gear after the transmission has warmed up.  Either the valve's not functioning, or the circuit from the transmission control module (TCM) to the solenoid is open.  Lowest hanging fruit is checking the harness under the truck on the passenger side; should be a small heat shield to remove and also checking one of the wires for ground continuity.  The solenoid requires some work to access from underneath the transmission with the pan off, so taking it to a shop depends on much you're willing to take apart.

 

P0420 and P0430 are the same codes, one for each side/bank of the engine.  It's unlikely that sensors on both sides and/or catalytic converters have crapped out at the same time, but because you're throwing both codes, there's something in common between bank 1 (cylinders 1, 3, 5 on passenger side) and bank 2 (cylinders 2, 4, 6 on driver side).  Possibly a leak somewhere along the intake (i.e., anywhere between the MAF, along the intake plenums, down to the fuel injector rail and intake manifold atop the engine), which changes the air metering the engine expects to burn.  There are metal gaskets at every connection; maybe there's a leak.  Could also be coil pack(s) related, but again, it's likely something in common...one bad coil pack might only trigger one of the codes, but not both.  Last time I was chasing those codes (P0430), it was due to ill-fitting fuel injector o-rings when I serviced them.  It was a frustrating process to figure it out, eventually discovered using a smoke machine to detect the leak.

 

Lastly, the oil leak.  Does seem likely valve covers.  I think the gaskets tend to leak at the front corners of them, near the 1 and 2 cylinder coil packs.  They do require RTV sealant in those spots and it wouldn't surprise me if it's time to re-seal those spots, particularly if it's not been done within those 277K.  If you're planning to investigate the P0420/P0430 issues on the engines top end, it's a good excuse to tackle the valve covers when you get things pulled off anyway.  The Engine Mechanical (EM) chapter is your friend here with all the torque specs and bolt tightening orders.  https://www.nicoclub.com/service-manual?fsm=Pathfinder%2F2002%2Fem.pdf.  Page EM-38 shows the points where RTV needs to be applied on each gasket.  Overall job will take a few hours.  Not a fun job, but also not too difficult.

[Slartibartfast]

Oil leaks can be a pain to track down. Valve covers are a good bet, though. Check and loctite (or have your mechanic check/loctite) the power valve screws while the intake is apart. IIRC there's an oil cooler on the VQ that tends to leak, so check that too.

 

+1 for going straight to the service manual. The later service manuals waste a lot of space telling you what buttons to press on the special Consult scanner that you don't have, but there's usually real diagrams/troubleshooting if you scroll down a little. For the trans code, I'd start with the circuit test at the top of AT-151.

 

Funny, my '95 had the harsh 1>2 shift too. My '93 has a softer 1>2 than it should. I haven't looked into it, probably an accumulator or something. Might be worth chasing if you drop the pan to go after that torque converter solenoid, but otherwise I'd let it be. Mine hasn't gotten noticeably worse over the past 30k miles, and I've got a replacement transmission waiting in the corner, so I haven't gotten excited about chasing the issue.

[hawairish]

14 hours ago, Slartibartfast said:

The later service manuals waste a lot of space telling you what buttons to press on the special Consult scanner that you don't have, but there's usually real diagrams/troubleshooting if you scroll down a little.

Oh man, the newer-newer style of FSMs around that 2005 point went straight to trash.  They used to be maybe 20 decently-defined chapters, but now there are like 40-50 chapters and they cover the dumbest micro-topics and just have you bouncing around from one chapter to another.  Reason #328 I'll never buy a Nissan newer than 2004.

[csprinkle]

Thanks for the replies! The quote for a valve cover gasket replacement was somewhere near an upwards of $2600 which seems outrageous, so I won't worry about the oil leak. And it doesn't seem like it would affect the car much so long as I keep topping off the oil.

 

Will definitely take a look at the factory service manual... Haven't really flipped through that too much yet. It honestly seems like I'm getting greedy with the mechanical condition of my pathy, as it basically runs flawlessly minus said conditions in my post above.

 

Thanks again for the pointers! I'll update if I attempt to fix anything.

[hawairish]

$2600.  Wow.

 

Honestly, I wouldn't neglect it.  What they're quoting isn't reflective of the effort required.  If you're a socket-and-wrench mechanic, that's all that job requires.  Parts and materials (valve cover gasket kit, manifold gasket kit, tube of RTV, splash of coolant) probably won't even run you $100, and the job needs little more than 10mm and 12mm sockets.  You don't even need to do the idle relearn like us 2003-04 owners.  Besides, might even address your other codes.

 

I didn't mention anything about your vibration issues.  If it's at idle, I suspect your motor mounts are toast.  Now, changing those is not a fun job.

 

[csprinkle]

I did watch a couple videos on YouTube of owners/repairmen doing the valve cover gasket replacement and it seemed to get really tricky and time-consuming. That said, I do have a good week-long stretch where I'll have another car available to commute with but I don't have the parts on-hand yet (oops). Just ordered "FEL-PRO VS 50608 R Engine Valve Cover Gasket Set" and "Permatex 82180 Ultra Black Maximum Oil Resistance RTV Silicone Gasket Maker" off Amazon. Was gonna run with Rockauto.com but the shipping/return process on Amazon works better for me.

 

I'll drop another comment if/when the valve cover gasket repair ever comes to fruition. I work 10s and I might realize pretty quick that working on my car is the last thing I want to do when I get off work Although I can always save it for the weekend. Thanks for the extra guidance again.

[csprinkle]

Okay - thinking that I might tackle the oil leak next weekend. What other sorts of repairs or maintenance should I look into while I've got it all dismantled? I've had some issues with ignition coils/spark plugs going bad in the past so is it recommended that I should spend time replacing all of them while I'm in there?

[hawairish]

Replacement on packs and plugs entirely depends on what sort of age, mileage, or wear they've experienced.  Usually can't go wrong changing the plugs, especially if you don't know when they were last changed.  Coil packs...usually not a need to replace them unless there's a problem (they're not usually cheap items x 6).

 

How are the belts?  Oil change?

 

Power washing the engine and underneath after all is said and done wouldn't be a terrible thing either.

[csprinkle]

Just did an oil change, not sure about belts/hoses/etc, will have to check my maintenance logs for that one later today. I could definitely do spark plugs since at this point I have no idea which has been repaired when since I did a bit of hot-swapping when I was troubleshooting my previous misfire code.

 

Any recommendations for spark plugs? I wouldn't mind getting 6 of these off Rockauto: NGK 96355 https://www.rockauto.com/en/moreinfo.php?pk=9779996&cc=1431960&pt=7212, is the extra price worth it on these ($11-ish each)?

 

I don't have access to any sort of power or pressure wash unfortunately.. Just a garden hose with a jet sprayer attachment but that probably won't suffice lol

[hawairish]

I tend to stick with NGK, as far as brands go.  Nissan OEM, tried and true.  As far as which flavor...the cost-to-mileage ratio used to be fairly linear, but it's gotten diluted as the cheaper plugs have just become overpriced and rival better-performing plugs.  In you case, going with those ruthenium ones you linked at $11/ea beats paying $10/ea for the OE-recommended double platinum ones (p/n 6240, a.k.a. PLFR5A-11) because you'll basically have a plug that far exceeds platinum tech in every way, including not having to replace them for another 100K-120K miles (vs. 50K-60K).  Ultimately, I'd love for you to keep that engine running up toward 400K!

 

Hose and jet sprayer probably isn't terrible.  Otherwise, get a can/bottle of engine degreaser, head to the local spray-n-wash, spray the degreaser on and let it sit a couple minutes, then wash it off.  Of course, a lot of spray-n-wash places have built in engine degreaser modes, plus a reduced spray for underhood use...but I like to go full blast.

[csprinkle]

Ordered 6 of the NGK 96355 spark plugs as well as an oil pan gasket, thanks for the NGK brand recommendation. Still haven't been able to check on my repair history for hoses and whatnot so I'll update the thread later on that. Again, aiming to do the spark plugs and valve cover gasket this weekend so I'll have more updates then. 

 

For the wash, there's a touchless car wash near me but I don't believe it has engine degreaser (it does have Rain-x though ). I'll look into that matter later, should probably show the engine bay some love too.

[Slartibartfast]

Look for a manual car wash, the kind that eats quarters and gives you time with the spray wand. Don't shoot it directly at electrical connectors or fluid caps if you can avoid it, otherwise give 'er hell.

 

I'd spray it down before you get in there. It's much nicer working on something that isn't an oily mess.

[csprinkle]

Cleaned out the engine bay with degreaser and a garden hose, doesn't look perfect but got some of the gunk out. I'm second guessing where the oil leak is coming from, looks like the valve cover gasket was actually replaced maybe 7 years ago (50-55k miles back). Back at square one with the oil leak.. Honestly have no idea how to diagnose what is leaking. All I know is that there is no smoke/burning oil when I drive.

[Slartibartfast]

Get it as clean as you can, run it for a bit, and see what gets oily again first. Might help narrow it down.

[csprinkle]

Get it as clean as you can, run it for a bit, and see what gets oily again first. Might help narrow it down.

Will do - I’ll share findings here when I can. Oil leak has fallen off of my priorities for the moment since it seems to be running well otherwise

[csprinkle]

For P0420/P0430, has anyone tried the O2 spacer mod on the downstream sensor to trick the car into making the codes go away? I've seen a couple people online use an "O2 Sensor 90° Adapter" with an optional "Mini Catalytic Convertor" attachment.

Edited September 3 by csprinkle
added names of products

[R50JR]

On 9/3/2025 at 11:47 PM, csprinkle said:

For P0420/P0430, has anyone tried the O2 spacer mod on the downstream sensor to trick the car into making the codes go away? I've seen a couple people online use an "O2 Sensor 90° Adapter" with an optional "Mini Catalytic Convertor" attachment.

I have done this with a different vehicle. On the downstream it works to trick the ecu, definitely don't use it upstream.

[csprinkle]

Unfortunate update I think I have some form of transmission shudder. Went to Les Schwab to confirm it wasn’t brakes/diff/hubs etc making the noise.  Sounds and feels like highway bump strips when driving 40-60mph. Any suggestions for how to proceed? My current plan is to get it checked out at a transmission shop somewhere and probably fix the torque converter clutch solenoid which is what P0740 suggests. Really hoping there’s nothing else wrong with the transmission

[csprinkle]

Or is it the front left manual hub making all that noise.. That’s what Les Schwab said it could be 

Edited September 5 by csprinkle

[hawairish]

On 9/3/2025 at 2:47 PM, csprinkle said:

For P0420/P0430, has anyone tried the O2 spacer mod on the downstream sensor to trick the car into making the codes go away? I've seen a couple people online use an "O2 Sensor 90° Adapter" with an optional "Mini Catalytic Convertor" attachment.

Ha, I just did this the other week to pass emissions (it worked).  But, a few things to know:

1. I started with Dorman 42109.  They're like a mile long and comically shiny for something you don't want to be visible, depending on where you are and how emissions are done (no concern for you since WA doesn't do emissions).  However, the length is fine for the driver's side, but on the passenger side it'd be a tight fit because the sensor will be up against the transmission.  I ended up not even opening the package and returned them.
2. I used Dorman 42009, which are shorter and also a little on the shiny side.  However, these need to be drilled out sufficiently to clear the sensor tip...
3. Lastly, and perhaps the most important part: keep in mind these are sold as "spark plug de-foulers/non-foulers" and are not meant for O2 sensors.  In my case, I realized that the O2 sensor on my passenger side has a tip that much larger than the sensor on my driver side.  So even after drilling them out, it would not fit on the passenger side without compromising the threads of the adapter.  If you go this direction and the O2 sensor tip is too big, this approach likely won't work.  A 90° might be okay and clear the passenger side.

[hawairish]

I'd be surprised is a manual hub is making noise, let alone causing any shudder.  Those are hubs are either engaged or they're not...and to that extent, they're either working or they're broken.  There's not really anything in between.

 

Rumbles at a speed range that tend to go away outside the range I almost always attribute to rear driveshaft.  Bad u-joints, specifically, but in some cases, a shift in the u-joint at the yoke causing the driveshaft have some an imbalance caused by excessive run-out.  But technically, any imbalance will do it.

 

...of course, if you have a transmission code, that's always suspect.

[Slartibartfast]

With the shudder and the code, yeah, trans shop is probably the way to go if you don't want to chase it yourself. I would do whatever electrical checks the service manual shows for that code on the off chance it's something simple.

 

My mom's Lexus GX470 did the same rumble strip thing when its torque converter clutch started acting up. My dad found a recommendation for some kind of shudder fix goo on a Lexus forum, and to our surprise (and to the surprise of the mechanic who put it in), the goo solved the problem. No idea if that's just a Lexus thing, or if it's worth trying in your case.

 

I don't think a manual hub could cause that rumble if it wanted to. If you want to rule it out, lock the hubs and see if the noise goes away.

 

I had an auto hub make noise once, but it was not a rumble. It sounded like a manual gearbox having its teeth kicked in. Scared the hell out of me.

[csprinkle]

The shudder seemed to be solved by engaging it in 4x4 mode on the hubs.


Sent from my iPhone using Tapatalk

[hawairish]

That's a head scratcher.  Locking the hubs would cause more thing to spin.  Unlocking the hubs would mean things aren't spinning, which makes it pretty hard for idle parts to cause vibrations.