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Old 05-19-2013, 02:17 PM   #1
gsbevli
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Default 2002 L300 Many Problems

Hi Everyone!

I have been a Saturn owner for 13 years (SL2 - The Greatest Car!) and based on my past experience I bought a used 2002 L300. It looked good and drove well. I checked and there were no trouble codes but I figured any that might arise might not be too troublesome. The AC was not cooling and I thought it might be a simple/cheap fix. Big Big Mistake.

Soon after the registration process was completed the service engine light popped up. In the meantime I showed it to a mechanic whom I trusted but in hindsight I realized was not exactly competent. The trouble code that popped up was P0128 - coolant temp below thermostat temp. They figured the problem with the AC was that the cooling fan wouldn't turn on when the AC was switched on (the compressor always did and we checked the freon levels - they were OK). So they figured the relay unit that was supposed to operate the fan was bad. We changed that, still nothing, so we changed the fan. Still nothing but by then I had realized my mistake and took it to the dealer. They said it was the compressor. So we changed that and the AC works fine now. The dealer said I would have to replace the thermostat and that would get rid of the code. I haven't done it yet but will be doing so soon.

So here is the current problem. Whenever the car has been driven sufficiently long to reach normal operating temp, if it is stopped for a moment, the engine dies. Basically the RPM reaches just at about the 600 rpm mark and then it dies. It starts up easily and if I rev it, it stays on but if I release the throttle, it dies again. Now, if I switch on the AC (which automatically increases the RPM) then it doesn't shut off. So I figured, after reading fdryer's posts that it probably is not the cps. It generally doesn't shut off while driving but it has happened on occasion when the AC is off and I slow down sufficiently for the engine to be running at idling speed. Most recently it happened, I also heard a chime, so I checked the trouble codes again and now in addition to the earlier code (P0128) there was another code: P0102 (Mass / Volume air flow circuit low input).

As I mentioned earlier, I do intend getting the stat replaced but I just want to find out if the experts out there (fdryer?!!) have some advice regarding the actual problem that might be causing the engine shut down.

PS: I forgot to mention that on a recent trip from LA to San Jose the AC air flow reduced considerably. After a short stop, it was fine again. Then again, after a while, the air flow slowed down to a trickle. I figured (in my infinite wisdom) that the the compressor is not being turned off once the car cools down (as I think it should) and that is probably forming ice around the evaporator coils that prevents free air flow (that happened to me once - in another car). So I started manually switching off the AC periodically and that solved the problem. Once we got to San Jose I checked that the compressor actually does not shut off even after the temperature of the air coming out of the vents is 30F. I don't know if that is by design or a fault and if it is related to the whole thermostat issue.

Any advice/opinion/commnets would be very welcome.

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Old 05-19-2013, 04:13 PM   #2
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Default Re: 2002 L300 Many Problems

1-Stop blaming me for anything I post. I'm a duck and can't take criticism.

2-There are several issues you inherited and some are obvious; the P0128 low coolant temperature requires replacing the t-stat (been there done that myself ) and may have a bearing on the engine dying out. If the engine sees too cold coolant then the ecm counters with more fuel that's used to quickly warm a cold engine but a constantly cool engine may be running excessively rich and may result in engine stalling. Replace the t-stat asap and see.

Without any mileage info, its easy to suggest some things to address;
a)Clean out the throttle body of built up deposits.
b)Clean the maf sensor with CRC Maf Sensor cleaner.
c)Remove and replace the (presumed) filthy cabin filter. Its hidden under the front window cowling, hinged with a simple plastic cover that's popped open like the hood to reveal the cabin filter. Top side tabs hold the filter in place - push them aside and pull the filter out for replacement.

Our R134a a/c systems have constantly running compressors that vary its output according to cooling demands. No more cycling compressors that were drastically loading/unloading the engine. Theoretically, R134a systems will not create the ice box scenario that R12 systems did due to using thermal expansion valves that virtually guarantees an ice-free build up. Usually with R12 icing, the ice block stops all air flow until the a/c is turned off and the block allowed to melt. The fan left running slowly pumps more air through.

Last edited by fdryer; 05-19-2013 at 04:20 PM..

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Old 05-19-2013, 05:19 PM   #3
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Default Re: 2002 L300 Many Problems

Thanks for the prompt reply fdryer. I will go have the t-stat replaced first thing tomorrow. The next on the list will be cleaning the MAF sensor and the cabin filter. I plan to do those myself unless the dealer gives me a really good price on those jobs. I wish I could replace the t-stat but that seems a formidable procedure.

The mileage on the car is 81000

Now, I know that replacing the cabin filter eliminates the possibility of it preventing free air flow but if it was that then air flow wouldn't have changed when we stopped the car for a while. If ice is unlikely, then could it be the resistor in the fan motor that controls fan speed? Because when the problem arose it didn't matter where I kept the fan speed, very little air came out of the vents. I can avoid the problem next time by just keeping the AC cooling knob slightly above the coldest setting but at the coldest setting with a thermometer in the vent I actually read a temperature of 30F. I don't know if the AC is supposed to do that. Could it be that the thermal expansion valves you mentioned aren't working properly? Unless they are a part of the compressor assembly itself, in which case it may be unlikely as we just replaced the compressor.

Thanks again, for your help.

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Old 05-19-2013, 05:42 PM   #4
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Default Re: 2002 L300 Many Problems

The txv resides in the firewall cut out where the two a/c hoses connect. The compressor is just that, a device to suction gas from the cabin evaporator coils and compress it to high pressure, discharging it into the condenser coils to cool off and change to a liquid under pressure. There's a high pressure relief valve attached to allow blowing off extreme high pressure above 525 psi - hazardous at this high pressure. An electric clutch coil, clutch plate and large idler bearing/pulley makes up a compressor assembly.

If you live in a/c regions of almost year 'round use then the blower fan may be wearing out. If you leave the fan speed on one medium setting, does fan speed slow down after awhile? This may be a clue to either a fan problem or something else.

The txv regulates cooling to stay above freezing and specs say they're set to about 35F so freezing never occurs. The majority of all lost cooling always results in warmer outlet temps due to loss of refrigerant. R12 systems losing refrigerant tended to develop freezing conditions by the nature of its ability to run and make every freezer in the world operate. R12 car systems didn't worry about the environment and needed the most rudimentary mechanism to regulate cold temps. The mechanisms used are what controls the temperatures and no one wants an ice box blocking air flow. Ice cold air but not ice blocking off air flow. The txv removes the icing tendency but not a failing blower motor. A slow moving blower moves less air and may feel like ice cold air until more air flows through the HVAC box.

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Old 05-20-2013, 01:37 AM   #5
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Default Re: 2002 L300 Many Problems

Quote:
Originally Posted by fdryer View Post

... If you live in a/c regions of almost year 'round use then the blower fan may be wearing out. If you leave the fan speed on one medium setting, does fan speed slow down after awhile? This may be a clue to either a fan problem or something else ...
Loss of cooling starts when we leave the fan on at the lowest setting. Once it airflow starts to reduce then even if we change the fan to 2 or 3, there is no change in air flow. And the air doesn't feel that cold anymore but that perception may be due to minimal air flow. This problem arises only when we go for a long (more than 1 hour) drive. Within the city where most drives take 30 minutes or less with stop and go traffic, we haven't noticed reduced air flow even if we leave the fan on the lowest. On long intercity drives speeds stay at 70mph or above for long periods of time. That in itself increases the efficiency of the AC but I wonder why that should affect air flow? Maybe if the fan stays on longer, the resistor gets hot and starts malfunctioning?

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Old 05-23-2013, 03:30 PM   #6
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Default Re: 2002 L300 Many Problems

Just a quick update:

1. I couldn't go to the dealer on Monday so I first cleaned the MAF sensor. I also changed the air filter. I let the car sit for several hours to make sure that everything was dry. I did not erase the trouble code. The car evidently sounded better when it was started and even after the temperature reached normal, the engine did not shut off. So I thought that problem is solved.

2. I took it to the dealer to have the t-stat replaced and got the car back yesterday. Since I hadn't erased the code, they picked up the 'MAF sensor low input' code and told me I had to change that sensor. I explained that I had already cleaned that sensor and that the code will probably go after a few cycles.

3. But since today morning the car has been misbehaving again. After the temperature reaches a tad above the 1/4 mark the engine dies if the RPM reaches at the 600-650 RPM mark which it does when it is stopped at a traffic light or one sows for a turn.

So could this mean a bad MAF sensor that needs to be replaced? When I saw the sensor there didn't seem to be anything other than two wires and, at least visually it seems, what could go wrong with such a sensor? Should I just replace the MAF sensor?

Also, as suggested by fdryer, I should clean the throttle body. Any guidance on how to do that?

Any thoughts/opinions will be greatly appreciated.

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Old 05-23-2013, 04:57 PM   #7
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Default Re: 2002 L300 Many Problems

The maf sensor is a precision air flow measuring device. Google for a how-to on its operation. The maf sensor and air snorkel must be clamped correctly to prevent air leaks. At this present time, its too early to tell if the maf sensor is faulty with little information given.

To clean a throttle, remove the air snorkel to see the throttle actuator. A good spray solvent or toothbrush dipped in solvent can dissolve deposits inside the throttle body. The throttle plate is spring loaded to stay closed so poking it open with a wooden or plastic tool can prop it open. The opening will allow better access to cleaning. Use care not to scratch the bore hole. Replace the air snorkel and be sure clamps are secure to prevent air leaks in and around the air snorkel.

A fuel pressure gauge connected to the fuel test valve on the fuel rail can be an asset in troubleshooting. Pressures not within range can affect engine running.

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Old 05-24-2013, 04:01 PM   #8
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Default Re: 2002 L300 Many Problems

Thanks fdryer. Your opinion and suggestions are a complete education in itself.

So I looked up the operation of the MAF sensor as you suggested and it seems the L300 has the resistive two wire sensors. I don't know if something can go wrong with the wires but I guess the electronics that is supposed to measure the resistance/current and convert those numbers into mass flow (g/s) can fail. However, to be sure, I did open the air intake line again, cleaned the throttle (it was very dirty) and cleaned the MAF sensor again. I disconnected the battery, gave everything about an hour to dry up and started her up.

It started without any problems and the engine seemed to be running without any hesitation. The 'service engine' light went away though the trouble code was in its memory. I cleared that code. After about 5 minutes when the engine temperature reached just above the 1/4 mark it sputtered and died again, just like it used to. The service engine light came on with the same trouble code. So I started it again, gave it some gas so that the engine doesn't shut off again. I cleared the code again and as soon as I left the gas pedal, it sputtered and died once again. Service engine light came on again with the same code. So maybe the sensor has failed.

The other thing I noticed when I kept the code reader on 'monitor' mode was that it showed mass flow of 0.12 lb/min. I thought that was low because I remember hearing someone saying that the minimum mass flow (at idling) should be 5g/s which converts to about 0.66 lb/min. Also, the mass flow shown on the reader did not increase or decrease even as I pressed or released on the gas pedal. I thought that should have changed. The other numbers (such as throttle position, short term fuel etc. all changed in response to a change in rpm). I don't know if I am missing something here but does this not confirm a bad MAF sensor?

I will be grateful for any thoughts/suggestion on this. I just want to be sure before I order a new MAF sensor (costing about $150) that a bad MAF is the most likely fault. If there are any other tests I could do, please let me know.

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Old 05-24-2013, 08:33 PM   #9
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Default Re: 2002 L300 Many Problems

OK, having set up my tablet, a Nexus-7 instead of my laptop to use OBDwiz, I was able to capture some maf readings for you to decide. At engine start up the maf readings stayed low, around 0.43 lb/min, revving in place to around 2k+ rpm, maf output went up to around 1.26+ lb/min. I seem to have comm issues of OBDwiz disconnecting at random and unable to record a freeze frame of data during local driving around the block. I wanted to see if I was able to record maf data at moderate rpm (above 2k) but the random comm disconnect interfered with this. I'll have to play around with some settings to stop the comm issues.

Based on what you found and my short data gathering with my OBDwiz/tablet, it would seem that your maf sensor is faulty.

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Old 05-24-2013, 09:08 PM   #10
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Default Re: 2002 L300 Many Problems

Check various online sources for parts, like rockauto.com, http://parts.nalleygmc.com/, GM parts online, etc.. You may be able to find lower prices.

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Old 05-25-2013, 01:32 AM   #11
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Default Re: 2002 L300 Many Problems

fdryer, you are absolutely amazing! Who would do this for anyone?! You did this test, on your own time just so that I could have a clear answer. I am deeply obliged and quite honestly, touched by your gesture. I hope someday I can do something that is equally helpful to you, though I doubt if I can be of that much help.

Your test has clearly demonstrated that the mass air flow readings should change when the throttle is opened and my code reader does not see any change in the MAF sensor data. So I have ordered a new sensor. I got the cheapest deal at Amazon with free shipping ($130 plus tax).

I will give an update after it arrives and I install it. I am hoping this solves the issue once and for all, but we'll see. The sensor is clearly faulty and needs to be replaced. I'll see if anything else comes up after this.

Thanks again.

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Old 06-04-2013, 01:26 AM   #12
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Default Re: 2002 L300 Many Problems

Here is an update that will, I hope, close out the thread on the right note. I got the sensor in the mail last Friday, installed it over the weekend and tested it out today. I disconnected the negative of the battery while I installed the sensor. The code reader clearly showed changing values of air mass coming from the sensor, from a low of about 0.38 lb/min at idling (engine at normal operating temp) to up to 1.3 lb/min at about 2000 rpm. That verified that changing the sensor did make a difference. The engine does not die anymore and runs very smoothly.

Finally, one question that is nagging me. Since the problem was a bad maf sensor which gave a constant low value for the air mass flow, how was the ECM able to increase fuel to the injectors? In other words, as I opened the throttle, since the MAF sensor reading did not change, why did the rpm go up? Is it that the fuel flow to the injectors is a combination of throttle position and MAf sensor data? Any opinion on this will be greatly appreciated.

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Old 06-04-2013, 02:11 AM   #13
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Default Re: 2002 L300 Many Problems

Somehow, engineering and software got together and said "something will go wrong and we have to try and anticipate what may fail". The map sensor is also part of the EFI system and is used as backup for load sensing when the Maf sensor fails. Automatic diagnostics determined the Maf sensor failed to work within its range of operation and went to a default program to allow driving. While not perfect, this allows some ability to drive somewhere for the eventual repair. EFI systems are more reliable than anyone wants to believe. Instant starting in any weather is one example.

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