Hey guys! I just recently purchased a 1992 SC400 after losing my 95 Camry in a tragic accident. I made the dumb mistake of buying the car from the owner without a Smog Check. I honestly thought that this high NOx (2200ppm) & HC (220ppm) issue could be easily fixed (and it probably can) but have been having a tough time trying to figure out what can possibly be wrong. My SC has 250,000 miles on it and does have some slight hesitation at times, although I'd say 90% of the time she runs like a champ. At highway speeds I do hear this roar when I let off the throttle, and at cruising speeds I do hear a slight tick. After reading the CL threads I believe it more than likely has a broken EGR tube. I have also noticed that my CEL does NOT light up with KOEO. I hooked up my Toyota/Lexus OBD scanner to check for codes and my scanner cannot connect to the ECU. I also cannot make the CEL blink by jumping the leads. I then took my SC to a very trusted repair shop to have my emissions components looked at. A few days went by and when I called to check up on my car, my tech told me they cleaned out the EGR twice and it still failed. He also replaced both Catalytic Converters without my approval (which ticked me off because I am absolutely broke!) and it still fails.


My question to you knowledgeable CL members is, how frequent is it to have a total ECU failure on these cars? I'm going back to the shop on monday to demand my car back so I can work on it myself. I'm very irritated that my shop has had my car for about a week and cannot properly diagnose my issue. I am a Diesel Mechanic by trade, so I'm sure it wont take me much time to find the root cause of the issue. But because my CEL light WONT come on at KOEO, and the fact that my scanner CANNOT connect to the ECM makes me think that my ECM is possibly toast. I am going to perform some routine maintenance (spark plugs, check coils, air filter) and check my EGR, Modulator, VSV, EGR pipe (replace if defective) & O2 sensors. If there is anything I'm overlooking please let me know! Thanks guys!

 

Welcome to the Forum!

Before you do anything else, IMHO, you should ask the Seller to pay for the Smog Certification as required under California Law or to take the car back. If the Seller refuses, have a Lexus / Toyota qualified independent or dealer do the repairs and take the Seller to Small Claims Court for remediating the problem (unless you know the Seller left the state or is a judgment-proof deadbeat.) If you bring the Lexus home and diagnose and repair it on your own you may not have a monetary claim. Small Claims Court can only provide a monetary resolution. The Seller is responsible for the test and certificate fees fi you ask for them in your claim as well as Court costs (if you remember to ask the judge to include them once you are at the hearing).

Under California Law the seller is required to provide a valid smog certification. From http://dmv.ca.gov/vr/smogfaq.htm:
"When a car is sold, who is responsible for the inspection?

The seller is required to provide the buyer with a valid smog inspection certification at the time of the sale or transfer. Smog certifications are good for 90 days from the date of issuance.

The inspection is not required on a transfer if a biennial smog certification was submitted to DMV within 90 days prior to the vehicle transfer date (a vehicle inspection report may be required for proof of certification).

NOTE: Smog certifications are not required for transfers that occur for a gasoline powered motor vehicle that is four or less model years old. (Determine the oldest-qualifying year model by subtracting three from the current year) the four or less model years old rule does not apply to diesel powered vehicles. A smog transfer fee will be collected from the new owner."

 

With all due respect I understand that I do reserve the right to demand the seller to ensure the vehicle passes all emissions testing prior to sale. But at this point it would be a big waste of my time & money trying to pursue the owner for a remedy to the problem. Especially when I'm sure the issue can be fixed quicker than a small claims court settlement.

So that being said I beg the question once again. How often do these ECMs fail on these cars?

 

Not very often if ever, Check the egr pipe on the back of the engine as they crack then leak and cause issues like this.

 

Thanks for the reply xspsi6! I know that any exhaust leak before the catalytic converter can contribute to high NOx readings. However I don't think that a broken EGR pipe can be the sole culprit of my extremely high NOx & HC readings (2200ppm & 220ppm respectively). I can see my AFM or O2 sensors as also contributing to such high readings due to the lean a/f mixture.

I feel it's imperative I rule out the ECM even though they're not prone to failure. I have to consider the fact that it's a 20 year old car & electronics fail just as mechanical components do. But again, thanks for your input. I greatly appreciate it!

 

Well I would think you are running rich to get such a high reading as the leaner the air fuel burns the hotter the fire which means more oxygen in the burn vs rich which would be more fuel in the burn but if the engine is expecting a certain amnt of exhaust gas and does not recieve it then I would say that the ecu would richen up the a/f mixture accordingly.

Here is what I would try : Clean the maf with maf cleaner then spray the throttlebody with carb cleaner while running to decarbon the intake manifold and then follow up with a seafoam treatment through the vac hose coming from the fuel pressure regulator,

If you are trying to pass the sniffer test make sure your car is god and hot before you attempt the test and also run some bottles of "heat" additive in the fuel before hand which I would say 1 bottle per gal of fuel as this is just alcohol and will lean things out a tad and not harm anything in the proscess.

If your car burns any oil then this will make the reading high as well which most sc400's on the road suffer from bad/worn valve stem seals.

This is just a little trick I learned over the years as a mechanic.

 

By the looks of the engine oil & the engine's behavior I know there isn't much oil consumption. I do plan on sending a oil sample to Blackstone on my next OCI. I changed the oil to Mobil 1 5w30.

Correct me if I'm wrong but arent high NOx readings are the result of high combustion chamber temps? When I read the sniffer pre test results I immediately thought of a lean a/f mixture because the fuel itself would serve as a coolant for the combustion chamber. Speaking of coolant, I also don't like the quality of the coolant in the radiator. I'm gonna have to also drain & refill the coolant system. In a way I cannot blame my tech for replacing the cats, but the cats were changed just a few months before the owner renewed his registration & it supposedly "passed". He did mention to me before buying the car that the right side cat needed replacement (probably because of the EGR pipe leak noise he would hear). But I'm pretty pissed that my tech started throwing expensive parts at the problem without really knowing if that was indeed the issue. It's clear he's not trying to help or he doesn't know what he's doing.

Enough of my ranting. I'm also skeptical of seafoaming my engine prior to an emissions test. I really don't believe stuff like seafoam will cure my issues. If anything it'll raise emissions due to elevated carbon levels by the burning seafoam in the chamber. And also, I've read a lot of threads on CL that cleaning the AFM/MAF does a lot more harm than good. Is there a special way of going about cleaning the AFM/MAF so I don't damage it? And also, what would be the best route on troubleshooting my in/op CEL light besides a possible burned dash bulb? That has to be another
major issue to my emissions problem.

 

Do you or did you by chance ever have a K&N filter on the car?

 

No, there is no K&N Filter & there is no evidence to suggest one has ever been installed. I'm sure if one was installed, the filter oil would leave the entire intake system gunky.

 

That was I was getting at and I may be thinking backwards on this emissions thing as I really do not have any 1st hand exp since we have no emission here in FL but in my sc400 the egr pipe cracked it caused all sorts of issues with how the car ran.

Seafoam works good if used properly however you can get the same result with water as all you are doing is steam cleaning the combustion chamber etc but seafoam adds a bit of lubrication so I just use it every 7-8k miles bu sucking it through the vacuum hose to the fuel pressure regulator.

 

Believe me when I say you're fortunate to not deal with all this emissions bull.

So I'm at the shop looking at the recent fail report & the new cats lowered my NOx to 1100ppm. However, I hate how my tech is going about troubleshooting the issue. He first replaced a very expensive part, & now he's trying to check the ECM for codes. He told me he's having trouble connecting to the ECM like I did, so he wants to check the ECM for power. At this point I'm fed up with the length of time its taken just to get to this part of diagnosis. The car is running excessively lean (CO levels at 0%, O2 levels at 3.0) so I'm really thinking there must be a ECM/O2/AFM issue at hand. Suggestions anyone?

 

Did you get your sc fixed? Sounds like you have a bad ecu. All of the Lexus have bad ecu's in some form. If you can't communicate with it that's a good indicator. I fix the ecu's for $175. That's a lot cheaper than the parts you will replace trying to figure out its bad. Once the ecu is rebuilt the car will run like new. The ecu is not the only problem with the sc but one of the first things to start with. Since you cant get a read with a code reader that tells me it's bad. Some of them will give you half reads or won't communicate at all. Let me know if I can help.

 

I know this thread is mighty old. But I'd like to finish what I started and give some other poor schmuck who is possibly currently in this situation some direction as to where he or she should start to fix this issue.

My emissions issue was trying to pass California's strict Enhanced Smog Inspection. High NOx (2300ppm) and high HC readings (300ppm) kept me from passing. Unfortunately my tech didn't really know much about my Lexus, and in a last ditch effort replaced my cats and sent it back for retest. Needless to say, it still failed. He tried to pull codes from the Diagnosis port under the hood and told me he couldn't retrieve any codes. He advised me to replace the ECU. I declined and asked for my car back and for him to reinstall the cats at no charge. And yes, he did so.

Upon receiving the car back I noticed that my check engine light did not come on at all. So I took the dash apart and replaced the bulb. Alas, my check engine light was on and alive. And there were codes stored. I pulled the codes with my scanner, using the diagnosis port UNDER the steering wheel dash. I had both Codes 25 (lean condition) & 27 (rear O2 circuit) codes on. I then looked for the proper FSM procedures here on CL to diagnose these codes. Both codes call for testing oxygen sensor voltages at the ECU with the car at idle and the car at high rev, which is what I did. All O2 sensors failed to meet the required specs. And needless to say, a set of 4 new Denso Oxygen Sensors did the trick and allowed me to pass emissions.

My advice to everyone on this forum is to please DIY as much as you can on your SC, or any car for that matter. Most shops that I encounter usually demonstrate more incompetence than competence. The forums are an EXCELLENT source of information to take on almost any job. I'd like to thank those who took the time to post up FSM material. It helped me out a TON! I saved a ton of $$$ on a gold shield repair station by doing the work myself.

 

I actually had a ECU failure on my 95 SC400, i'm in FL so smog test was never an issue. When my ECU failed i could not get any readings, but shortly before completely failing it did have code 71(EGR malfunction) MY ECU would cause a high idle, the RPM"s would jump, If i turned the AC on the car would shut off. Eventually after completely failing i could only keep the car running if had my foot all the way to the ground when starting and keeping the RPM's above 4500(meaning i couldn't take it out of park) Replaced ECU and it fixed everything including the CEL. My old ECU had black burns all through it, meaning it shorted out. Not sure this helps any, but hope it does. BTW Bert epic signature.

 

My 95 SC400 also had the same issue few months ago - had code 25 (running lean) and would not pass the smog.

What I did:
1. Replaced both main O2 sensors with Denso. However, after a trip to Vegas, code 25 showed up again.
2. After searching on the net (clublexus and other forums), I did the following:I was so pissed off.

Finally I took my car to my regular mechanic and per his inspection, the reading on the both main O2 sensors were fluctuating out of the specifications. Since I had replaced the O2 sensors, he assumed the false readings came from one of the cats or the fuel injectors had failed. He was leaning toward the cats than the fuel injectors.

One of ClubLexus members advised me to take my car to Mike at Lex Mastertech in Pasadena - Mike is well known to have an extensive knowledge in Lexus world. Mike did a thorough testing - mechanical and electrical. He also replaced the TPS and still no luck. No vacuum leak was found and the MAF was clean and working properly. He checked every thing there was that had caused the car running lean, but he found nothing was wrong. I told Mike about the other mechanic's suggestion to replace the cats, but Mike insisted that Lexus cats would not fail if the car has been well maintained throughout its years which I did (always buy Chevron since day 1). He also mentioned that I didn't have to replace the fuel pump either - rarely Toyota fuel pump will fail. Oh well ... I already did it anyways since that was an easy DIY.

The timing was also perfect (I replaced the timing belt & water pump 4000 miles before I had code 25), so what's the problem? We decided to take all 8 fuel injectors out and sent them out to RC Engineering in Torrance (http://rceng.com) to get them all cleaned and rebuilt. It was cheaper than buying new ones. Note: ClubLexus members get 10% off. Before the service = the condition of 6 injectors were "okay" and 2 were "dripping" fuel instead of "spraying". After the service, all 8 injectors were back to their specifications. Cool.

But guess what ... After all this things that I went through, code 25 was still there.
WTF.
I was about to sell the damn thing!
Mike did another thorough testing, checking all electrical connection, ECU pin connection and all was good
However, all the tests that he did always pointing back to the O2 sensors.

He decided to replace the passenger side main O2 sensor and voila ...... code 25 was gone.
So ..... in the beginning I bought 2 main O2 sensors (Denso) and 1 of them failed after driving to Vegas.
Be advised I bought the sensors directly from Denso retailer (http://www.densoproducts.com)

So folks, for code 25, first please check your main O2 sensors before you start spending money at anything else.