Catalytic Converters & P0240's
(I decided to re-write the original post to better convey diagnostic methods and thinking in terms of P0240 codes)
Diagnosing Catalytic Converters seems to be one of the most commonly misunderstood topics on the forums, the issue stems from how the vehicle determines catalytic converter health. Most, if not all manufacturers stick to a relatively basic method of using a pre-cat Oxygen Sensor or AFR (Air/Fuel Ratio) Sensor in combination with a downstream Oxygen Sensor after the catalytic converter. While this method is pretty much the standard of Catalytic Converter Efficency monitors in modern vehicles and for the most part is a fairly decent method of determining the catalytic converter's operation...for the most part. The inherent problem is that the PCM (Powertrain Control Module) uses the AFR/O2 sensors to test the catalytic converter, this is not a truly effective test.
AFR/O2 Sensors only measure the oxygen content in the exhaust system, a catalytic converter actually works with 5 different gases in a complex chemical reaction to reduce emissions. The oxygen is actually stored and used by the catalytic converter in this chemical process to convert hydrocarbons to NOX, CO, CO2, & H2O; this storage is what the sensors are really reading. Its not so much a test of the catalytic converter's ability to perform its job as much as its ability to store oxygen. Like I said, for the most part this works well and its been a standard for the automotive industry for decades. The issue comes in when the PCM starts getting information from the O2 sensors that it doesn't like. When that happens you get the dreaded P0240 & related codes, the thing that most people fail to realize is that this doesn't actually mean that the catalytic converter is junk; it just means that the PCM THINKS its junk.
This is a very important statement that I think a lot of members and technicians overlook, a DTC (Diagnostic Trouble Code) is a code set by the vehicle's system for a fault that it THINKS it has. Whether or not that problem actually exists is up to the technician to verify, the PCM makes its judgement based on the information that is provided to it; if it gets bad data it will think it has a problem and set a DTC (people who work on P0300's know what I am talking about.) This is where proper methodology comes in handy, before jumping to "I need a new catalytic converter because I have a P0240" you need to verify that the catalytic converter itself is bad.
Unfortunately, the only 100% accurate way to verify a catalytic converter's operation is to do an "intrusive test" which means drilling a hole into the catalytic converter and using a 4 or 5 gas analyzer to verify that it is indeed breaking down hydrocarbons. I realize most people don't want to go drilling holes in their cat, I just want to be clear that an intrusive test is the only 100% accurate method in testing a catalytic converter. That being said, their are perfectly valid tests that can be performed to give you a good idea of the catalytic converter's health. Many techs like to use an IR thermometer to measure pre and post cat temperatures and that often works okay, though the heatshields can skew those measurements some. Another method involves using a 4 or 5 gas analyzer in the tailpipe to look at emissions and see if anything is actually being chemically broken down. Most people though use the O2 Sensor data to determine if the cat is indeed working right, I mean that's how the PCM does it right? This isn't a bad way to start your diagnostics, but you have to keep in mind that it is possible the data you are reading is incorrect. O2 Sensors can become slow, biased, and sometimes give weird readings as they age and/or fail.
After checking to see your sensor data looks okay, you now need to verify that the O2 Sensors are doing their job. A standard O2 sensor will cycle between about .100mv to .900mv indicating rich or lean mixtures, the PCM tries to keep the readings from the sensor in the middle by manipulating the Fuel Trim. If you happen to have a DSO, now would be a good time to back probe into the O2 sensor wiring and watch it cycle. If you snap the accelerator pedal to WOT and then let off, you should see the O2 Sensor spike from bottom to top within 100ms (miliseconds,) failure to do so indicates a faulty sensor. Another indicator is if the sensor is biased, meaning if the voltage seems to stay towards one end of the spectrum no matter what you do. If you don't have a DSO, you can look at the Fuel Trim (even if you have a DSO its still a good diagnostic tool) to see if the vehicle isn't running too rich or too lean causing the cat to work ineffectively; it is very possible for the vehicle to run rich or lean enough to set a P0240 but not set a rich or lean code. A large majority of the time faulty O2 Sensors (pre or post cat, or both) are the cause of these codes and I recommend you replace them in bank pairs (i.e. Bank 1 Pre & post AFR/O2 Sensors.)
If your diagnostics do show that the catalytic converter has actually failed you need to stop and think for a moment before you just slap a new cat on there. Catalytic Converters do not go bad by themselves, in a normally operating vehicle a catalytic converter should easily last the life of the vehicle if not into the 300k+ range, something caused the catalytic converter to fail. What your diagnostics have found is a SYMPTOM of another problem with the vehicle and putting a new catalytic converter on will not fix the problem that caused it to go bad in the first place! This is something to keep in mind when dealing with these codes/repairs, because I have seen guys slap a set of sensors and cats on a car and have it come back with the same problem months down the line because the real problem trashed the cats again.
There are other things to consider, such as if the vehicle has been driven with faulty sensors for a long time sustained damage to the catalytic converter may have occurred and it will need to be replaced anyways. The sensors may have damaged the cat but it could be "brought back to life." I have seen catalytic converters be brought back to life before, but really its a 50/50 shot in the dark.
Here are some links:
HowStuffWorks "How Catalytic Converters Work"
http://www.converterwarehouse.com/te...rter-&News=100
Catalytic Converter Tech Tips
Catalytic Converter - Front, Driver, Center - Exhaust | DriveWire.com
http://www.autoserviceprofessional....anding-and-diagnosing-Toyota-P0420-DTC?Page=3
HeadGaskets
As we all know, where there are engine blocks and cylinder heads, there are headgaskets. Its been a known issue that the 1GR-FE's Headgaskets have been rather subpar in terms of the usual reliability and quality we've come to expect from Toyota. Not saying every engine is going to give the ghost on their gaskets, but we do have an update headgasket design for a reason. So the important question, how the hell do you tell if your 4Runner has developed an appetite for that sweet pink fluid? Well, hopefully this will help shed some light on that subject!
First off lets get into the basics of what a headgasket does, it helps seat the deck (the top of the engine block's cylinder bank) with the cylinder head. The headgasket is the single most important sealing component of an engine, has three main jobs. The first is to seal the compression of the piston in the cylinder bore during engine operation, the gasket needs to hold up to brief moments of high degrees of temperature, high pressure, and all on a continual basis. The second & third functions revolve around sealing the coolant and oil passages from each other and the cylinder bore itself.
When trying to diagnose a blown cylinderhead gasket you want to keep in mind the function of the cylinderhead gasket and the various problems a failure will cause as individually these problems could be symptoms of something different, while combined present a case for a blown headgasket.
The first and most obvious symptom of a blown headgasket is coolant loss as the coolant either burns in the engine or is mixed with the oil, both bad things by the way. If you remove the radiator cap (be careful to do this with the system unpressurized or you could seriously injure yourself!) and run the engine you may see bubbles in the coolant as the engine runs. This indicates that the headgasket has failed enough to allow cylinder pressure to bleed into the cooling system and coolant to bleed into the cylinders. They'll look more like soda carbonation than big rolling bubbles that you'd see with a pot of boiling water. Another way to test if you have a blown headgasket with the radiator cap is to use Radiator Test Strips that work much like the test strips you use for a pool, you dip them into the coolant and it will let you know if it is full of unburned hydrocarbons (this can also be done by putting a 4 or 5 gas analyzer above the radiator cap with the engine running. An obvious sign of a blown headgasket is sweet smelling exhaust as glycol based coolant will tend to smell sweet as it is burned, keep in mind not all cylinderhead gasket failures spew tons of smoke.
Oil contamination and/or consumption is another symptom of a blown headgasket (keep in mind that this symptom by itself can be many things), if your oil looks milky or smells like sweet like coolant you can probably guess that there is a blown gasket. This is a fairly accurate diagnosis as there are few places where coolant can readily mix with engine oil in an engine other than at the junction of the engine deck and cylinderhead.
The drivability problems resulting from a failed headgasket are also a good way of verifying that these individual symptoms lead to the same conclusion. For example, due to the gasket being burned out, cylinder pressure could be bleeding into another cylinder causing low compression on some cylinders. Along with coolant and oil intrusion into the cylinder bore, your vehicle will often rough very rough, sputter, or at times even stall if its serious enough. Removing the spark plugs and checking for milky residue, or wetness (there's a difference between coolant and fuel soaked plugs, it takes some experience to tell right off the bat, but if it doesn't reek of gas its a fairly good indicator,) is a good first step, I would then recommend that you perform a compression test on all the cylinders if you have a tester, this will help you get an idea if pressure is bleeding into other cylinders.
There are a lot of other possible symptoms that could be attributed to a blown headgasket and you need to address them as you perform your diagnostic, as this will help you determine how much damage the powertrain has sustained as a result. For example, lets talk abouta worst case scenario. Where the gasket has failed catastrophically bleeding coolant, oil, & cylinder pressure into each other and the engine has been run for a while in this condition; this is a combination that is sure to make most owners think their vehicle is beyond saving. The reality is that barring an overheat, the engine can be salvaged and the vehicle brought back to working order, the following is what I would recommend to a customer who has brought in such a vehicle.
[What the vehicle needs to correct the current issue]
-New headgaskets, both banks (even if only one is leaking, I would recommend two because the labor vs. peace of mind in my opinion is worth the investment.)
-New O-rings & Gaskets/FIPG for removed components (i.e. V6 Timing covers use FIPG, thermostat, intake gaskets, ect)
-New thermostat
-Coolant Flush
-Engine Oil & Filter Change
-New Spark Plugs
-New AFR & O2 Sensors (In this hypothetical case, the customer has been flooding the exhuast with coolant/oil mixture and will have contaminated these sensors)
[What I would also recommend at the time of repair, since the engine will be apart to save time on labor]
-Drive Belt
-Fuel Injector Cleaning (I like Seafoam)
-Check & Adjust Valve Timing (if vehicle is higher on mileage)
-Replace PCV Valves
-R&R Water Pump (if it has not been done yet)
-Check Chain & Replace if stretched beyond spec (V6 Only)
-R&R Timing Belt (V8 Only)
Noises
This is one of those things that comes up a lot on any forum and are often the trickest for a forum or individual to address without actually being there, so I am going to try and break it into a couple chunks and go over some simple, yet helpful ways to go about diagnosing these pesky acustical nightmares.
Clunks, Clanks, and Thumps
So the first and most important thing about trying to diagnose a noise complaint (or for that matter any complaint in general really) is to make the noise happen! Before you laugh me off the forum, hear me out. You need to make sure you can reproduce the sound consistently otherwise you'll be waiting for it to happen rather than actively hunting it down.
Once you've established that you have to hold the car in 3rd gear, with the foot 3/8 the way on the brake pedal while tapping the gas to the harmony of "The Imperial March" (or whatever funky way you need to make the noise happen.)
There are two ways to check the noise from here, we'll start with the standing still in the stall (assuming the noise can be made without having to actively drive the vehicle.) It helps to have a second person stand outside of the vehicle and walk around to identify where the noise is coming from and possibly even pin point it. You may need to back up & pull forward a couple times, drive down the street slowly with the person walking next to you, ect ect. The idea here is to narrow down where the noise is coming from before you waste time throwing it up in the air.
The scone way to do this is to have a second person (if possible, if not you can do this by yourself) listen to the vehicle when you're driving it down the road to once againt pinpoint where the noise is coming from and how it is being caused.
Once you've found the general area (or even pinpointed the sound to a certain component) you have to start thinking about the problem at hand. This tends to be easier for spatial thinkers as you basically need to think of what components make up the area the noise is coming from, when and how the noise occurs, and what components do what at that time.
For example, when hitting a bump you hear a rattling noise from under the vehiclek, but the noise is also heard under heavy acceleration and lightly at idle. At this point the causes can be numerous depending on where it is coming from. Lets say you and your assistant have narrowed the noise to the front end of the vehicle closer to the bottom of the engine bay area. You can now rule out valvetrain, top end noises, ect. But you have the bottom end of the engine to deal with, the suspension, and frame.
So you and your assistance determine the noise is coming from the bottom of the engine area and it is a loud mettalic rattling like cans on a string. Your assistant bangs on the skid plate and doesn't hear it rattle, so you remove it and test drive the vehicle again, the noise is still present. Now you need to think of what items would be loose enough to rattle but not cause drivability issues and safety issues as at this point the vehicle drives great and no lights are on. By process of elimination and understanding what fits down in the engine you can now rule out suspension components, engine block internals, mostly anything that isn't loose sheetmetal, brackets, and/or fluid lines.
Now that you know you're looking for a loose heatshield, bracket, and/or loose lines you can easily find the loose catalytic converter heatshield once you've liften the car in the air.
I realize this sounds very complex, but once you start thinking in that diagnostic mindset it literally can take you minutes to pinpoint an odd noise and know with a high degree of accuracy what is the problem without ever lifting the vehicle in the air.
Gear & Powertrain Noises
These are more difficult to diagnose as you may be able to find where the noise is coming from, but often it is inside a larger component such as an axle housing or transmission. You can also easily mistake the cause of the noise as it may have multiple possible issues (i.e. a gear growling could be a wheel bearing, pinion shaft bearing, no fluid for the gears, improper backspacing of the differential to the pinion gear ect.)
These types of problems rely heavily on understanding how the components work together and how different states of activity affect the assembly as a whole. Lets take for example a noise we've all heard, a low metallic growling when driving down the road. This noise can be anything, but for the sake of example, lets say we've kind of decided its coming from the front of the vehicle at a decent speed and gets worse at higher speeds, also it is present in reverse when accelerating and not present when revving the engine.
Logic tells us if the noise increase proportionally to the speed of the vehicle we can assume it is a driven component of the drivetrain rather than an issue with the engine (this is reinforced by the fact that revving the engine does nothing in regards to the noise.) We've eliminated the transmission, transfercase, rear driveshaft, and rear axle because its coming from the front. So we have wheel bearings, axle bearings, differential & pinion shaft bearings to deal with here.
So how do we find out which it is? Well, when driving the vehicle and replicating the noise if you turn the steering wheel left or right slightly does the noise go away? If so, this indicates a wheel bearing as the turning of the wheel unloads the bearing from the worn section (that causes the noise) and thus reduces or eliminates the growl, now you just have to figure out driver or passenger side and you're home free!
What if the noise is still there? Well, now you need to figure out if the noise is harmonic (i.e. does it just growl all the time or does it only happen say 65-75mph?) If its only happening in a particular speed range, from the center of the front of the vehicle, then more than likely it'll end up being an interal issue with the ring gear & pinion shaft bearings. (This is by the way how we determined my failed Pinion Shaft bearing
)
Parastitic Drains
This isn't something I haven't seen on the forum very often but I figured it'd be worth mentioning regardless. Parastic Drains/Draws are the mystery gremlins that devour your battery overnight, they are a pain to find on modern cars versus older vehicles and are a common issue with modern computerized vehicles.
So in this section I will be going over diagnostic methods and aides in tracking down these pesky electrical gremlins and hopefully help members in more efficient testing/repair methods in this regard.
The first thing you're going to need is a Low-Amp Clamp and a DVOM (Digital Volt/Ohm Meter) and/or DSO (Digital Storage Osciliscope) to properly test the vehicle. You want a LOW-amp clamp (something like a max of 60amps) vs. a regular one that will read up to 600amps; the reason being a finer accuracy in the lower amp range as you will be measuring miliamps rather than full amps. Now some of you will want to try and figure it out with just a DVOM and you can do it this way, but you'll be wasting more effort and energy trying to track the problem down by voltage versus current draw (also your DVOM, depending on quality may have expensive fuses that many people commonly blow trying to use them for current testing, so I highly recommend you avoid amperage testing with a DVOM.) The more correct and efficient method is by measuring the current draw; you'll also want to brush up on your Ohm's law for this section, just in case.
Now that we have the tools lets go over the basic methodology regarding tracking down a parasitic drain. As a general rule of thumb with the vehicle completely turned off, doors closed, lights off, key in pocket; you want no more than about 50miliamps (this is a rule of thumb, some vehicles like European vehicles can have as much as 200+miliamps) of current draw from your battery. Now don't get your hair in a knot if the vehicle does draw some current, this is normal. What you need to establish is what your "baseline" draw is, which can be difficult. Manufactuer's including Toyota don't have a specification of what the baseline current draw on their vehicles is, more troubling they don't explain what the times are to get a baseline reading. What I mean by that is the amount of time it takes from turning the key off and exiting the vehicle for the current draw to stablilize to its lowest possible point. It varies from vehicle to vehicles, modules stay awake for as much as an hour after turning off the vehicle before going to sleep, you can see as much as 300~400 miliamps after turning off the key, slowly tapering off to 150miliamps after say 10 minutes and then finally dropping to 30miliamps after about 40 minutes; this being your baseline current draw (these numbers are arbitrary and vary from vehicle to vehicle of the same make and model.)
I would recommend patience when testing for parastic draws, this can be very frustrating for some people who want to solve the problem right now or don't have a lot of time to work on their vehicles. What I recommend is hooking up your amp clamp, turning the key off and monitoring the battery draw. Wait ten minutes and check it again, then come back in another half hour and check it again, after about an hour if the number has stayed the same by that time you can more than likely assume that is your baseline current draw.
Once you have your baseline current draw you can begin your diagnostics, at this point I would recommend checking voltage/amperage draw at some common areas I see;
~Aftermarket Alarm Systems
~Aftermarket Audio Set-ups
~Aftermarket Modules such as BlueTooth, Remote Start, Battery Management Systems
~Modified Wiring
These are common red flags for parasitic draws I see regularly, also often show up as electrical issues elsewhere in the vehicle as well when improperly (and sometimes even properly) installed/set-up. If you don't have anything like that and/or have already eliminated them as possible parasitic draws I would recommend unplugging modules one by one until you see your amperage draw drop. Sometimes you'll see the entire amount drop, sometimes you'll see part of the draw drop, this is another issue where it can make diagnostics frustrating. In the case of a single module drawing too much current you're going to need to bust out the wiring diagram and start testing the circuits to find out what/where/why the module is drawing so much amperage, this is where ohm's law comes into play. Connections, wiring issues, corrosion, failing components can result in excessive resistance causing the system to do funny things. In the case of multiple modules drawing current, you might need to make a judgement call which module is drawing "excessive" current and/or should not be on at the that time (this is another part where it can get frustrating as there are no specifications on what stays alive and doesn.)
For example, lets say your Keyless Entry Module stays awake drawing 25miliamps and the PCM stays alive drawing 40miliamps (again arbitrary numbers and modules chosen to provide an example.) The keyless entry module might need to stay in this sort of "sleep" mode as it is watching for a signal from your key fob and needs to have some power to the system. While the PCM maybe doesn't need to be on, but is for whatever reason drawing current (some Prius and Toyota models will wake up randomly to run an EVAP test of the system and then shut off.) You'll want to start your diagnostics at the PCM and deterimine again what/where/why this current draw exists.
Finally and I realize this last paragraph will basically seem to make everything I've just written pointless, but please bear with me here. You may not be able to properly and/or definitively diagnose what the cause of your parasitic draw is. In many GM's the OnStar module needed to be reprogrammed because it stayed awake when it wasn't supposed to. Many "reflashes" for vehicles are not announced via TSBs or even by the manufacturer and are buried (if at present at all) in obscure information sources that you have to pay for, sometimes the solution is just a reflash of a module to correct the problem (I haven't seen any reflashes for the 4th gen 4Runners, Toyota has had a habit of not relying on reflashing as often as other manufactuers.) I know this basically throws this entire section out the window for many of you and I empathize with yout as it is equally frustrating for technicans when we are being paid and expected to at the very least find what the problem is, let alone fix it.
This is a more "advanced" section of vehicle diagnostics that will be difficult for many of you to attempt, again this entire thread is designed to provide a guide line for people to start their diagnostics or the very least be able to understand the amount of effort, training, and skill it takes to repair modern vehicles. This is by no means a complete guide to diagnosing parasitic draws, but rather a starting point/guide to starting diagnostics as it easily gets more complicated when you talk CAN communication and module status/activity.
Some reference material for those interested in further reading:
http://www.examiner.com/article/diagnosing-parasitic-draw-and-excessive-resistance-problems
http://www.diagnosticnews.com/featured/parasitic-battery-drains/
J/K)
