fasted1953

I have a 99 GS400 with 95K miles. I've been getting the all-too-common P0171 CEL code on and off for quite a while. I've been up and down the CL forums and have tried most of the fixes. I'm still getting P0171, and I can smell fuel in the exhaust. The car runs smooth and perfectly in every other way. The CEL seems to come on when I'm in stop and go traffic, creeping up a few feet at a time, not cruising.
Here's what I've done:

- Replaced MAF.
- Fixed broken nipple on back of resonator with brass nipple (Lexus dealer in austin broke it and never told me, just glued it back on).
- Replaced various hoses coming off the resonator.
- Checked for vacuum leaks on the top of the engine with a spray bottle/soapy water. Didnt find any leaks.
- Retorqued the spark plugs on driver side (bank 1). Spark plugs were changed at around 50K mi. Used Lexus stock plugs.
- Replaced air filter.
- Cleaned throttle body.
- Replaced heated oxygen sensors.. forward ones.

Here's what I havent done:
- I think there's a couple hoses from the resonator that go towards the bottom of the engine. Power steering maybe? Didnt check the bottom end of those.
- Original ECU.

Any suggestions about what else to check would be greatly appreciated. At this point, I'm thinking of replacing the O2 sensors (the ones closest to the engine, not the exhaust ones)

Wondering if I should just let my mechanic (ex-lexus dealership master mechaic) have at it. Are there things they can read on their computer to help narrow it down, or will they just be guessing at it like I am?

BCP43002

Could be any of these:
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
ECM

ivnnln

iTrader: (1)

Keep us update on what's your findings, pls. I have the same code as yours too. I am leaning toward the Idle air control valve, but still poking around to find out more details. I have cleaned the MAF, throttle, inspected all hoses, and reset the code. If it cames back, then I might just replace the IACV.

fasted1953

Air induction - stock induction, I've checked and my mechanic has also. No induction or vacuum leaks found. I fixed the broken nipple on the back of the resonator with a brass fitting.
Injector blockage - mechanic checked for codes, etc. Nothing abnormal about fuel pressure or injectors. No misfires recorded.
MAF - I replaced it a month ago or so. Decreased the frequency of the code, but they still come back once in a while.
Gas leakage - I have not checked and I'm not sure how to do it. I would hope that my mechanic did check for cracks in the exhaust manifold. Sounds like they knew about that as a possible cause.
O2 sensors. No O2 sensor codes recorded. I have new sensors and will be changing them to see if it helps.
ECM - I've been told that this is rarely the cause. I'm hoping its not. Was told that ECM problems usually cause transmission problems, not P0171.

Dont know about the coolant sensor. Where is it located and is it a hard thing to change?

BCP43002

I don't know if it is the same location in a 400 but in a 430 it is on the engine block, pass side, about even with the power steering reservoir, off one of the leads from the wiring harness.

ivnnln

iTrader: (1)

There are two coolant sensors. One is on the enginge block the pass. side, and the other one is at the bottom of the radiator tank driver side (it's call the sender coolant temp) I think on the GS400. I replaced the one on the engine block but not at the radiator yet. Just curious, do you upgrade your intake system to K&N one? Not just a drop in filter.

lexus ASM

Let me check the code on TIS. I can PM you the diagnostic sheet if you can PM me an email address.

Goodluck.

fasted1953

(ADMIN: Could you move this to GS gen 2? My bad for starting it in the wrong place)

fasted1953

I'm running the stock intake manifold and Toyota air filter. No K&N intake for me!

Today I changed my front two O2 sensors. The driver side was a b*tch to change. Used penetrating oil, but still couldnt break it lose. No room to get an O2 sensor socket in there, so I used a 7/8 open and box end wrench. Worked the sensor back and forth to avoid stripping the threads. Was careful but it didnt help. Stripped the threads a little bit. Sensor came out with metal in the threads. Fortunately, I decided to have a sparkplug tap/chaser on hand before I started. Best 8 bucks I ever spend. I was able to get the threads cleaned up pretty good with a little breakfree clp and the tap. Then I couldnt figure out how to get the wire connector off. Not a lot of room to get in position to see how it clicks in. Finally figured out that you have to press the release from behind and wiggle it with all your strength. Finally got it lose, put in the new one carefully with plenty of anti seize. Threads were fine, thank goodness. Passenger side was uneventful. The car seems to run better, idles stronger. Time will tell if this was the cure. I'll have to wait and see if the CEL/P0171 comes back on. I'll try to remember to post whether it did the trick.

fasted1953

Replaced the heated oxygen sensors. Got them from oxygensensors.com . Hassle free and great price. Car seemed to run much better.

A few days later, the CEL and P0171 code was back. GRRRRR.

Today, I took off the engine cover to find the ECT sensor. I was going to replace that next. I decided to look for vacuum leaks one more time. Got out the spray bottle with soapy water and started squirting. This time, I heard a hiss when I sprayed around the throttle body area. First, I thought it was just the water steaming when it hit the hot intake manifold. Then I saw the bubbles moving. Got out a length of pvc pipe to listen closer.

I think I finally found the real problem!! The PCV valve hose that goes from the front of the intake manifold to the PCV valve was loose, and cracked on the bottom. Moved it around to get a seal, looked at the dash, and the CEL was gone! Took off the hose, used electrical tape to bind the split closed and put it back on. Used a hose clamp to get a better seal. So far so good. I'll be ordering a couple hoses at Lexus tomorrow, along with a new PVC valve. In 95K miles, I've never replaced it because I never knew where it was.

Hopefully, I found the real source of the problem this time. I'll let you know.

tom steele

be careful taking the pcv valve grommet out mine feel apart and i had to fish it out with needle nose pliers kragen carries both the grommet and pcv valve for a lot cheaper than the lexus dealer i need to go get that hose too. mine is in bad shape as well..

fasted1953

If the hose is cracked like mine was, wrapping it with electrical tape, then heating the tape like shrink tubing and using a screw type hose clamp will do the trick. I limped around on that fix for about a week with no problems. When I had a hell of a time getting the tape off to show my mechanic the break in the hose. Finally had to cut if off with a utility knife.

Thanks to the good folks at Auto Zone in NW Austin for that shade tree fix. They were just glad to know I wouldnt be coming around to get the CEL code read any more.

fasted1953

Its been 10 days since I found the cracked hose and patched it. I got the hose, PCV valve, PCV valve grommet, PCV valve cover from Lexus and did the replacement. Replaced a couple other hoses, related to the fuel vapor stuff that were showing their age while I was at it. Since the patch, no CEL!

In the diagnostic info, it lists vacuum leaks as the first or second thing to look for. I think it was a combination of things in my case, but there were definitely two vacuum leaks. One was easy.. the broken nipple on the resonator that the Lexus dealer in Austin broke off and tried to glue back on. Never told me about it. The second leak was the split PCV valve hose. I think the idiots at the Lexus dealer might have split that hose at the same time as they screwed up the resonator... a couple years ago when I had to have the starter replaced.

Lets look at all the collateral damage caused by John Roberts Lexus in Austin service department:

1. Put in a bad starter and didnt tell me. Had to take it back for a second replacement.
2. Broke the nipple off the resonator, glued it back on and never told me. Eventually it came loose.
3. Broke the coolant crossover pipe. Gooped it back together and didnt tell me, but it was leaking almost from the first day I got it back.
4. They probably split the end of the PCV valve hose when they removed it from the manifold, and it took until now before it split the rest of the way.

If you live in Austin, TX or are just passing thru and you need service on your Lexus, just sell the car or burn it. You'll hate yourself if you take it to the city's only Lexus dealer for service. Better yet, call me and I'll help you get it up and running again.

Its taken me a couple of years and a lot of money to undo the damage caused by that dealerships service department. I love my GS400, but I'm not sure the free loaners, donuts and coffee are worth all the aggrevation involved in dealing with the dealerships.

Thank god for this web site and all the fanatic GS owners who post here. I'm not a mechanic. I'm a software engineer. Why can I find and fix this stuff and they can't?!?!

</rant>

GS4_Fiend

iTrader: (22)

Nice post. Amen.

LexusK

iTrader: (14)

I got this code about a month ago but haven't been able to go get it checked out yet. Weird thing is, the CEL went off like a week ago. Was it just a malfunction?