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Car Forum / Lexus Cars / September 2006Where Do I Start Looking?
I own 4 Toyotas and one Lexus (too many kids) and the Lexus just threw me for a loop. '94 Lexus ES300 with 168,000 miles suddenly stalled while stopped at a light. Rolled to the side and tried to start it but no luck. All the dash board lights light up like normal so power was there to the gauges and starter motor. Waited about 5 minutes and it started fine with no check engine light. Hooked up my OBDII laptop and there are no diagnostic codes or problems recorded. O2 sensor readings: One looks funny. O2 sensors B1 S1 and B2 S1 plots look fine with sensor voltage (or current) and fuel trim or lambda both going through a sine wave dance. Fuel trim staying between 0 and 4. O2 sensor B1 S2 looks funny: sensor voltage (or current) on the low side and fuel trim or lambda is pegged at 100. I didn't know this thing had 3 O2 sensors (at least that's what my computer is trying to tell me). There has been an intermittent trouble code about every 7 months of P0300, P0301 & P0303 (Random/Multiple Cylinder Misfire Detected, cylinders 1 & 3) but no hesitation or performance issues when it happens. I just clear the codes and wait for it to come back. I'm starting to study the service manual but I'm having trouble figuring out where to start without some kind of diagnostic code. Paul. Phoenix, AZ >I own 4 Toyotas and one Lexus (too many kids) > and the Lexus just threw me for a loop. [quoted text clipped - 7 lines] > my OBDII laptop and there are no diagnostic codes or > problems recorded. If there is no check engine light, the likelihood of a code being stored is pretty low. > O2 sensor readings: One looks funny. O2 sensors B1 S1 > and B2 S1 plots look fine with sensor voltage (or [quoted text clipped - 5 lines] > sensors (at least that's what my computer is trying to > tell me). If you have 2 catalytic converters, then you probably have 4 O2 sensors - B1 S1, B2 S1, B1 S2, and B2 S2. In other words, a sensor before and after each catalytic hconverter. If the catalytic converter is doing its job, the signal from the post-cat sensors should much flatter than the signals from the pre-cat sensors. If you look at the factory service manual under DTC P0430, it should show what the o2 sensor patterns should look like. > There has been an intermittent trouble code about > every 7 months of P0300, P0301 & P0303 [quoted text clipped - 9 lines] > Paul. > Phoenix, AZ The cylinder misfire codes could be caused by ignition system misfires or from an over-lean fuel mixture. If you have aftermarket ignition parts, consider using OEM next time you change them because I have seen some aftermarket ignition parts cause problems. Some aftermarket ignition parts are fine and some cause problems. I have not been able to detect a pattern so I recommend OEM ignition parts. A lean-misfire usually brings up other DTC's unless the pre-cat sensors are beginning to fail, but your scan seems to indicate that they are OK. As far as what caused the car to stall, I would check fuel pressure with a fuel pressure gauge. A fuel pump or fuel pressure regulator that is not up to stuff or a clogged fuel filter might not deliver sufficient fuel pressure to keep the engine running and they would not necessarily set a check engine light. I would check the fuel pump, fuel pressure regulator, and fuel filter in that order. A failing fuel pressure regulator often causes long cranking during cold starts, which you did not mention, and a fuel filter that is clogged enough to starve the engine for fuel would probably not allow a re-start, leaving the fuel pump as a more likely culprit.  SignatureRay O (correct punctuation to reply) Ray, The "funny" sensor is the one after the catalytic converter. Only one converter on the car. The manual does say that the patterns should look calmer. I'll start looking at the fuel delivery system (but I have to buy the tools first). I got this car from my brother-in-law about 6 months ago so I really don't know the service history as he also bought it used. Only things I've done on it is timing belt, waterpump, crank seal, four shocks and a lot of touch up paint (Colorado car, lots of gravel there in the winter.) There is no problem with power of the engine and it easily runs 80 MPH. Car starts just fine, no long cranking. But I'll check fuel system performance (any excuse to buy more tools!!) I'll probably dive into the MAF meter, IAC valve and throttle body and see how dirty it is and change the fuel filter this weekend. Thanks for the ideas Ray, at least I have a starting point now. Paul. > If the catalytic converter is doing its job, the signal from the post-cat > sensors should be much flatter than the signals from the pre-cat sensors. > If you look at the factory service manual under DTC P0430, it should show > what the o2 sensor patterns should look like. >> There has been an intermittent trouble code about >> every 7 months of P0300, P0301 & P0303 >> (Random/Multiple Cylinder Misfire Detected, cylinders >> 1 & 3) but no hesitation or performance issues when it >> happens. > The cylinder misfire codes could be caused by ignition system misfires or > from an over-lean fuel mixture. If you have aftermarket ignition parts, [quoted text clipped - 15 lines] > probably not allow a re-start, leaving the fuel pump as a more likely > culprit. > Ray, > > The "funny" sensor is the one after the catalytic converter. Only one > converter on the car. The manual does say that the patterns should look > calmer. If the after-cat sensor is active with a pattern like the pre-cat sensor, I would imagine that you get have DTC P0420 because the cat is failing. The cat may be on its way out but not bad enough to set a code yet. > I'll start looking at the fuel delivery system (but I have to buy the > tools first). I got this car from my brother-in-law about 6 months ago so [quoted text clipped - 6 lines] > Car starts just fine, no long cranking. But I'll check fuel system > performance (any excuse to buy more tools!!) No long cranking tends to rule out the fuel pressure regulator and fuel filter but the fuel pump can be bad. > I'll probably dive into the MAF meter, IAC valve and throttle body and see > how dirty it is and change the fuel filter this weekend. Thanks for the > ideas Ray, at least I have a starting point now. > > Paul. If the car idles OK, the IAC valve is probably OK. If the throttle pedal sticks in the closed position, then the throttle plate (butterfly plate) in the throttle body may be gummed up and need cleaning with carb cleaner. A gummed up throttle body will not cause the engine to stall. If you do not have a volt-ohm meter, it would be a good investment. Good luck! SignatureRay O (correct punctuation to reply) > If the after-cat sensor is active with a pattern like the pre-cat sensor, > I would imagine that you get have DTC P0420 because the cat is failing. > The cat may be on its way out but not bad enough to set a code yet. The after-cat sensor is the same pattern but much less amplitude. I'll watch it though. Maybe I'll run the car around with the OBD laptop attached and record the patterns with different RPM's and load. > No long cranking tends to rule out the fuel pressure regulator and fuel > filter but the fuel pump can be bad. Good to know!! Once I get the fuel pressure gauge I can check the whole system out. > If you do not have a volt-ohm meter, it would be a good investment. Electrical gear I have. Digital and analog VOM, ampmeters, etc. I'm better at electrical problems than mechnical but I like working on both. Thanks for the help Ray!! Paul. >> If the after-cat sensor is active with a pattern like the pre-cat sensor, >> I would imagine that you get have DTC P0420 because the cat is failing. [quoted text clipped - 3 lines] > watch it though. Maybe I'll run the car around with the OBD laptop > attached and record the patterns with different RPM's and load. Similar pattern but much less amplitute is good because that means that the cat is cleaning up the nasties. If the patterns match frequency and amplitude - in other words, the same signal, then the cat is not working. >> No long cranking tends to rule out the fuel pressure regulator and fuel >> filter but the fuel pump can be bad. [quoted text clipped - 10 lines] > > Paul. You can probably diagnose 95% of the electrical components in a car with a good digital meter, and if you know how to use it, even better! The crank position sensor that someone mentioned is worth checking out, although I would imagine that a problem in that circuit would set a MIL and DTC. In terms of thinking about problems that would not set a MIL, the fuel pump is a possibility. Good luck! BTW, what kind of OBD laptop are you using and where did you get it? SignatureRay O (correct punctuation to reply) I use an old laptop and plug in an adapter into the OBDII connection. It allows me to see plots of O2 and several other systems. It also will log data and save it for review. Viewing and resetting trouble codes is easy. I think it only reads the power train codes (Pxxxx). The connecting cable came from OBDII Automotive Diagnostics http://obddiagnostics.com/index.html and the software and upgrades are free with the converter purchase (OBDII interface $83; CAN interface $77). He also sells the parts if you want to make it yourself and the electrical drawings/schematics are on his site for free. One work of caution though, the OBDII connection needs a serial port to plug into. The newer laptops do not come with a serial port anymore. That's why I use an old laptop. The older ones are readily available and are more bullet proof that the newer laptops (2 to 3 year life expectancy before hardware starts to fail on the high end units). Biggest problem with the old laptops is the batteries are old and don't hold a charge and I'm too cheap to buy new batteries. The unit got a nice write up on http://www.4x4wire.com/toyota/4Runner/tech/BR-3/ . There are some reviews of connecting cables at http://www.obd-codes.com/reviews/showcat.php/cat/4/page/ . Paul. > BTW, what kind of OBD laptop are you using and where did you get it? >I use an old laptop and plug in an adapter into the OBDII connection. It >allows me to see plots of O2 and several other systems. It also will log [quoted text clipped - 21 lines] > > Paul. Thanks for the info! I have a couple of old laptops sitting around, maybe I can put them to better use than as a doorstop. I'm not sure that I can justify another scanner, even though it is better than the one I have, especially since you can check just about everything out with a DVM, but maybe for the next go-around... SignatureRay O (correct punctuation to reply) >I own 4 Toyotas and one Lexus (too many kids) > and the Lexus just threw me for a loop. [quoted text clipped - 31 lines] > Paul. > Phoenix, AZ I don't know for sure on yours, but I do come across a similar fault on Vauxhalls in the uk. 9 times out of ten it is the crank position sensor. mrcheerful I'll have to check the wiring on that sensor. It was in the way a lot when I changed the water pump and timing belt. I may have pulled on it too much. Thanks, Paul. >>I own 4 Toyotas and one Lexus (too many kids) >> and the Lexus just threw me for a loop. [quoted text clipped - 36 lines] > > mrcheerful |
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