baerster

Hello,

My 1998 LS 400 (177k miles) intermittently turns on Check Engine and gives me these codes and turns off the VSC:
P1346 (Variable Valve Timing Sensor Bank 1 Range/Performance Problem)
P1351 (Variable Valve Timing Sensor Range/Performance Problem Bank 2)
P1346 P
P1351 P

The engine runs smoothly and doesn't present any other problems.

On the possibility that the problem is the sensors or actuators being clogged with dirty oil, my mechanic did a hot oil engine clean, then I put 1/2 can of Seafoam into the engine oil.

After I reset/clear the codes with a code reader, the car works fine for anywhere from 5 miles to 20 miles, then the check engine light comes on again and the VSC turns off.

Any advice on how to diagnose this, to determine if it's just the sensors or if it's a deeper problem? What does it signify that both banks of the engine are affected - anything?

I would love to get this fixed but only if it's not an indication of a deeper problem that would take more than the value of the car to fix.

timmy0tool

iTrader: (7)

see the following:
https://www.clublexus.com/forums/per...ve-filter.html

https://www.clublexus.com/forums/ls-...cv-filter.html

https://www.clublexus.com/forums/ls-...lfunction.html

baerster

Thank you! I will try the filter replacement and see if that fixes the problem. I am new to this car - what reading in this forum to you recommend for someone who needs orientation to how to evaluate the condition of the car and the expected life left in the engine and other major components, and also to know what other maintenance I should do now?

Legender

Question has been asked and answered before. Little searching would find this:
https://www.clublexus.com/forums/ls-...sed-ls400.html

Good luck.

timmy0tool

iTrader: (7)

Copy+Paste from another thread:

The Unofficial LS400 buyer's guide
Good morning everyone. Since my LS is about to go into the shop again, I wanted to share my experience owning it and a GS400, creating a thorough buyer's guide since I see these questions pop up pretty often. Of course feel free to contribute any other tips you might have and maybe we can make this into a sticky post for potential buyers. Disclaimer: I'm not a professional mechanic nor do I work for Lexus. I'm just an enthusiast who loves these cars, obsesses over keeping them on the road in good condition and does a lot of DIY. I have an aerospace engineering background but no formal training on cars.

ENGINE

The most important items on the 1UZ engines are the timing belt and water pump. They should be changed every 90k-100k miles and there is a sticker under the hood, usually on the engine cover, that should state the date and mileage of the last change. 90-94 cars have a non-interference engine, meaning that if the timing belt jumps or snaps, your engine will just die but no mechanical damage will occur. 95+ engines are interference, so loss of timing will cause the pistons to hit the valves and result in catastrophic failure. When buying a 95+ car then timing belt change becomes more critical. It's good to do anyway because the water pumps start seeping around that mileage anyway. Make sure they change the idler pulleys, tensioner pulleys and hydraulic tensioner when they do the job or you do it yourself, 99% of shops will.

Cam seals and the crankshaft seals have a tendency to leak. You will notice by seeing an oily mess on the front of the engine, coming from behind the timing cover. In bad cases it will even drip on the ground. It is normally suggested to replace these while doing the timing belt and water pump service, so don't cheap out and ask for it to be done. 98+ cars also have a seal in the VVTi gear that can leak, so do that while you're there as well. I've had to do all three in three separate occasions (read: labor $$$$) because I was being a cheapskate and the shop I used wasn't keen on "while we're there" maintenance

Valve Cover Gaskets. These usually start to go around 60-80k depending on your luck. You will notice by a little wetness around the valve cover itself, or in really bad cases by dripping towards the rear of your engine. If it's really bad it will leak onto your hot catalytic converter releasing a puff of smoke when you're at a standstill. You can also pull a spark plug and see if it's oily as the spark plug tube seals usually fail at the same time and should be replaced as part of the job.

Vacuum recovery box. There's a plastic box along the intake tube that goes from your air filter to your throttle body on the 98+ cars to which several vacuum lines attach. The nipples for these lines are made of plastic and snap off on most cars, resulting in people jerry rigging hoses with RTV (I've even seen electrical tape!). You can check this easily by just removing the engine cover and taking a look. This can cause vacuum leaks and should be addressed. You can buy barbed brass fittings at the hardware store, drill out the hole where the old nipple was to enlarge it and screw the fitting in, putting some RTV around the joint for safety. Be careful not to crack the plastic in the process as it's very thin. Check the forums for detailed instructions on how to do this.

Hoses. Check them to make sure they're soft. With the age and heat most of these have gone hard and brittle. If you ever work on your car and plan to remove a hose, make sure to buy a replacement as it will crack when you pull it off.

Serpentine Belt. On high mileage cars check the tensioner and idler pulleys and make sure there's no bearing noise. They're cheap and easy to replace so I suggest doing it next time you change your belt on a high mileage car.

POWER STEERING

This warrants it's own sections as it's one of the biggest issues with these cars, especially the first generation ones. The main issue is that the pump will leak on almost all cars, and conveniently leak onto the alternator, frying it and leaving you without power. Make this the first thing you check on every car. First generation cars can also leak from the power steering reservoirs onto the alternator, but the reservoir location was moved I believe in 98. Also, if power steering fluid level drops but you don't see a leak, or if there's a puff of white smoke on startup, then you have a leak from the idle up valve that uses vacuum to raise the idle when the power steering pump is operated. It's screwed in to the pump and has two vacuum lines coming from it. You can read lots of info on the power steering system from the ClubLexus Power Steering Bible

SUSPENSION

The #1 suspension issue with these cars are the strut rod bushings. They usually fail around 100k miles and you can tell on the test drive if you're front end feels very loose over bumps. It can also cause a slight vibration when going 60-65 mph or a shimmy under light braking from highway speeds that will be felt in the steering wheel instead of in the pedal like warped rotors normally would.

Lower ball joints should also be replaced if the cars have over 100k. They're heavy cars and wear them out faster than other models. If grease is leaking from the boot, then it's time to replace. Grab the wheel at 12-6 and at 3-9 with the car jacked up and shake it. If there's play, then it's time to replace. You can do them when changing the strut rods as it's a pretty simple job compared to many other cars.

Sway Bar Bushings can also go bad. You can tell if there's a creaking noise going over bumps, like an old door opening. They're also cheap and take about 10 minutes each side to replace.

ELECTRICAL

On 90-97 cars, the ECU capacitors tend to leak causing all sorts of crazy issues. The most common ones seem to be hard starting, rough running, OBD port that won't communicate. I personally have a 99 so I haven't experienced any issues, but there is a wealth of knowledge in this thread. The ECU can be rebuilt by a specialist either by mail-in or locally if you live around one, and it's not too expensive if I remember correctly.

The instrument cluster has two main failure modes. The LEDs on the needles can go out, leaving them dark, or the Speedometer and/or Tachometer needle will be stuck at zero. Both can be solved by sending it out for rebuild. There are several places in the US that offer this service for the LS400 and it's around 120$.

Corroded grounds can give funky electrical issues, including a no-start condition where the starter will click once then the whole car will just go dead as if there were no battery plugged in. It will usually start and work properly after pulling the negative battery terminal for a couple of minutes then connecting it back. You can follow the instructions on this thread to check the condition of your grounding points and replace any corroded component (part numbers are included). I had the intermittent no-start issue and replacing all parts in that thread cured it after a relatively straightforward fix.

TRANSMISSION

The transmissions on these cars are very solid, and I haven't really experienced any pressing issues aside from these two things.

On the first drive of the day, it will hang in 2nd gear up until around 2600 RPM even if you're easy on the throttle then slam into 3rd. Just once. Afterwards it will never do it again. All the 1UZ Lexuses I've driven do this and the consensus seems to be that it's normal and can be programmed out by changing some components in the valve body. TransGo sells a kit online for around 70$ IIRC.

I've seen some cars throw a P0763 "Shift Solenoid C Electrical" code intermittently that will clear itself after one or two days. It seems to be more common on the GS400 and my GS did that a couple of times, but never on the LS. Could be possibly caused by a particle in some dirty transmission fluid getting stuck in the solenoid then clearing out and some have reported fixing it completely after a transmission flush, or some electrical contacts in the solenoid getting bent out of shape. On my GS draining and filling the fluid a few times only fixed it temporarily and it was resolved by replacing the solenoid.

BRAKES

Brakes on these cars don't seem to have any issues. If your car is a 90-94, consider upgrading to 95+ brakes as they are a lot more effective. It's a direct bolt on swap but you will need to run at least 17" wheels to clear the larger caliper and rotor.

Please feel free to contribute anything that I might have missed or not experienced, to make this guide as thorough as possible. Also feel free to correct me if I made any mistakes and I will edit as quickly as possible. Hopefully we can make a sticky thread out of this for future reference.

ENGINE AND TRANS MOUNTS

These have a big effect on the ride quality in the car.
A bad transmission mount can show itself in many ways but the most common one is a phantom like vibration you feel when accelerating through 1800-2000 RPM. It's a kind of flutter sound, similar to when you go high speed with the windows open but will be very difficult to discern and your passengers might not even feel it. I have very sensitive hearing so it bothered me a lot. You can also put your hand on the shifter and if you feel a vibration in that rev range, it's probably shot. Honestly it's probably shot anyway at high miles, costs around 50$ from the dealer and takes 30 minutes to change so there's no reason not to.
Engine mounts are more of a pain and I used a shop for mine. The 1UZ should be able to have a glass of water put on it's intake manifold and show no ripples. If it shows many ripples, or you feel lots of vibrations or a shaking at idle and when revving, even in neutral, then it's probably the mounts. All three of mine were split in half at 145k when they were changed.

EDIT: Added info on engine and trans mounts.
EDIT 2: Loaner LS400 that I tried also had the 2nd gear hanging issue in the morning so it is a design thing. Found the supplier of the valve body rebuild kit (TransGo) and edited accordingly.
EDIT 3: Added info on issues caused by corroded grounding points in the engine bay and how to check them