I have an 02 Cavalier with a 2.4L (VIN T) in it. I came home from deployment to find it has a CEL that won't go away. Prior to purchase, the car had a complete exhaust system installed (full length tube header and magnaflow exhaust kit from header back), a cold air induction kit, and an under-drive pulley on the alternator. I scanned it and found it has a P0171 DTC. I replaced both O2 sensors and cleared the codes. The code came back. I noticed the engine is running extremely rich though. I replaced the MAP sensor and the timing chain (gears, guides, etc). I cleared the codes and the light came back on once again. I borrowed a scanner and monitored O2 data while sitting in the driveway and while driving. The upstream O2 sensor reads .450 volts at idle on initial start up. Once the accelerator has been depressed the O2 voltage drops to 0 volts and never comes back up. I took it to a Chevrolet dealership and verified that the PCM software is stock and that no computer modifications have been done. If I unplug the O2 sensor and clear the codes, the P0171 will go away and the O2 sensor voltage will stay steady at .450 volts. However, a P0134 O2 sensor circuit inactivity code will pop. I'm racking my brain here and have no idea where to go chasing these gremlins. Any input would be greatly appreciated.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
What are your fuel trims reading
- 2004 Cavalier - 124k, owned since new
I'll have to check the fuel trim when I get home from work today. I know the car is running extremely rich though. I pulled the plugs and did a compression check because someone told me the rings may be washed out. I had between 225 and 230 between all four cylinders. The plugs were very black with carbon due to too much fuel. It is also blowing a lot of carbon out the tail pipe, especially at WOT. I read in another forum where this was described to look similar to a diesel exhaust under acceleration. I checked for vacuum leaks and cannot find any. I did notice there is what sounds like a turbo sounding whine coming from the front right of the engine bay when I am under hard acceleration, however the car does not have a turbo or any kind of forced induction. I have checked most of the engine harness for chaffed or damaged conduit or wires and found nothing. I haven't checked the exhaust yet for any leaks, however, I cannot hear any. That doesn't mean there isn't any and I know this. The one thing that concerns me though is that the bung for the O2 sensor blowing the code is in the collector immediately where the 4 primary tubes enter it. I have questioned whether or not this is too close to the primary tubes as not all cylinders fire at the same time and therefore the scavange effect of one tube on another may be causing an air pocket around the O2 sensor causing it to think the engine is lean. But I will definitely check the fuel trim numbers when i get home from work this evening.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
The P0171 code is a lean code. Your getting to much air or not enough fuel. By getting that code your o2 sensor is working correctly. Check your fuel filter, your air filter and all the air intake ducting for possible leaks. It could also be a clogged injector.
Dan
I know the P0171 is a lean code. However, my fuel delivery system is dumping fuel into the cylinders, thus producing the carbon fouled plugs and the massive amounts of carbon and unburnt fuel coming out of the tail pipe. I can guarantee that my fuel delivery system is not the cause of a lean condition considering the engine is running extremely rich. However, the fact that the engine is running extremely rich doesn't explain why I am getting a P0171. I can also guarantee that the O2 sensor is not the issue. I have replaced it multiple times with new sensors.
Based on some research I have done on this site as well as discussions that I have had with both GM dealerships and other ASE Certified Technicians, I have some homework to do before I can post further test results. As soon as I have those, I will post what I discover and give as much more information as possible. But right now, all the information I have on the conditions and performance of the vehicle has been posted in my previous posting on this particular topic.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
With sensor 1 plugged in, the fuel trim reads
ST TRIM BANK 1 (
49.2
LT TRIM BANK 1 (
27.3
This change with engine RPM, and continuously changes withengine RPM and trottle position. The readings were taken at idle. With sensor 1 plugged in, the sensor voltage is at .450 volts and drops to 0.00 volts once the engine RPM's go up. The sensor voltage never comes off 0 volts until the ignition is cycled off and back on.
With sensor 1 unplugged,the fuel trim reads
ST TRIM BANK 1 (
0.00
LT TRIM BANK 1 (
21.9
This does not change with engine RPM. Again the readings were taken at idle. With the sensor unplugged, the sensor voltage is at .450 volts and does not change.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
The stupid faces are suppose to be percent signs inside parenthese.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
Ok, so I have devised a plan that has worked several times on avionics gear, but I have never tried on a vehicle. I need someone to help me with this though. If someone with an 02 Cav with a 2.4 could measure the resistance on the purple wire to ground and teh tan wire to ground and the purple wire to the tan wire, all this on sensor 1 at the engine harness side of the connector for sensor 1 with the ignition off, I think I may be able to find my proble. I have used this technique to pinpoint problems in high tech radar equipment in my daily job, but never on a vehicle. I don't have a known good around to compare my readings to. If nothing else, it would indicate which side of the circuit is havingthe problem. If you could also check the voltages at the same connector with the key on / engine off, that may help remarkably too.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
You added "a cold air induction kit" is your IAT (idle air temp sensor) in place?
Yes, my intake air temperature sensor is in place and plugged in. I thought about this though and think that if this was faulty, the O2 sensor receiving an erroneous reading would be able to compensate. I.E. if the IAT were reading cold and the car was running rich as a result, the O2 sensor would detect this rich condition and be able to compensate for the rich condition and vice versa should the IAT be reading abnormally warm and the fuel system be trying to compensate by leaning out.
I have ruled out a stuck injector. If I had an injector that was stuck closed thus causing a P0171, (1) the engine wouldn't be dumping fuel out the exhaust the way it is, (2) the plugs would not all be carbon fouled, and (3) I would have a noticable miss fire.
I have ruled out a vacuum leak on the intake side. If I had an intake leak, The O2 sensor would be able to compensate. If the O2 sensor couldn't compensate, I would (1) have a really horrible idle, and or (2) the car wouldn't run at all.
I have ruled out the cam phase as well. I replaced the timing chain, the cam gears, crank sprocket, guides, and tensioner. So I believe the cam shafts are in proper phase and in time IAW the factory specifications.
I have ruled out washed out piston rings or bad rings. If I had bad rings, I would (1) be consuming oil, (2) not have 225 to 230 pis in all four cylinders, (3) have a miss on whatever cylinder had the bad rings.
New developement though. Since I cleard the codes a week ago to get the fuel trim numbers, the CEL has not come back on. The O2 sensor has been unplugged the entire time. I am going to get under the car sometime today or tomorrow and do a more intensive inspection for an exhaust leak. I have been thinking about this "turbo whine" noise I spoke of earlier and think that it may be an exhaust leak in the header or at the collector. I think that the exhaust gases rushing over the leak is creating a venturi effect and sucking in fresh air at or near the O2 sensor, also causing the noise that I am hearing. I will post my discoveries within the next couple days. But otherwise, all the sensors, with the exception of the upstream O2 sensor, are plugged in and seem to be functioning.
I really wish that those trying to help me with ideas and what not could see the car, drive the car and watch the data in the scanner. This thing is nothing I have ever seen and is just racking my brain. I can't understand how nothing on the intake side has a problem, yet it is throwing a code that would suggest that something on the intake side of the head is at fault, unless there is something I am not thinking of, in which case any ideas or input I get from everyone is considered and investigated.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
Well, I changed out the IAT (Intake Air Temperature) sensor yesterday and yet I still have a P0171. The sensor data change for the IAT, but it didn't fix my original problem.
I'm losing my mind here. Anyone have any new ideas?
Some people have brain storms, others light drizzles. And then there are those that have droughts.
Do'es the header have a coating on it I've seen it 1 time before , where the coating would stop the o2 senser from grounding and it did the same thing as your car is doing . Hope this helps .
I'll be under the car tomorrow and will check this out. I'll re-post after I poke around a bit.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
Get a smoke test done. You could have a bad gasket somewhere on the intake part of the car that is sucking more air into the intake.
Dan
Ok, well for 30 bucks, replacing the intake gasket and throttle body gasket wasn't difficult at all. I even cleaned all the components as best as I could. I did discover that the o-ring on the IAC was missing and I replaced that. I sprayed everywhere that there could possibly be a leak and could not detect any changes in the engines idle or at idle performance. However, the data in the scan tool has not changed since the repairs. Any new ideas would be greatly appreciated.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
Thanks Luis for the information. Unfortunately I have checked everything that the flow chart you sent me says to check and then some, and to no avail.
Earlier in the forum, I mentioned that I unplugged the sensor and the CEL has not come back on. I had the scanner in it today after replacing the intake and throttle body gaskets, and the IAC solenoid o-ring. I cleaned everything as best as I could with carb and choke cleaner. I think I may have a bad IAC though as the engine will idle high and slowly come down to a normal idle. I think the IAC is just slow responding or reacting to commands from the PCM. I am waiting now until payday to replace it see as how I just dumped over $600 in parts into the front end of my Blazer.
I am starting to wonder if the IAC is just not closing all the way, enough for the idle to stay down when the O2 is plugged in and the fuel system is trying to compensate, but not enough to keep from appearing to have a false vacuum leak and kicking the P0171.
Now, even with that said, I was also under the car and inspecting the exhaust and discovered the weld around the header pipes into the collector appears to be cracked but have no carbon tracking as if it were leaking. I'm not saying it isn't leaking, it just doesn't appear to be. And with the O2 in the collector, I think this too may be part of the problem. If it is, it opens another can of worms in that I haven't found a muffler shop in the state of Virginia that will touch a tube header because they believe for some reason that they are illegal.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
This might be a retarded question, but have you checked the header gasket itself? I've seen shops forget to put them on. It could have gotten broken as well during install. Also make sure the header bolts are torqued properly too. Both of these things could cause extra air to get sucked into the exhaust before the O2 causing the lean code.
I've also found frequently when your scratching your head with something like this, number 1, step away. Let it go for a day or two. Start fresh.
Two, it's always something stupid. Always.
I am curious to know your findings though, because we have a car in the shop that's doing the exact same thing your car is doing. O2 voltage at idle is .42x and a soon as you give it throttle it drops to 0. The only difference is when you get off the throttle completely (moving or not) the O2 voltage comes back up slowly. One other difference, this car is a 94 OBD1, so it's even more of a bitch to diagnose.
If ur IAC was stuck, the car would not run. I had a 02 Eco that would not run bc the IAC choked the car and stalled it. So I doubt thats bad. The lean condition is obviously causing ur car to run rich as hell. That crack in ur header could very well be the issue. If you have it, I would throw the stock header back onto the car. Try and eliminate the problem. Ur O2 is seeing too much air, and trying to compensate it with throwing a hell of alot of fuel with it. So ignore the running rich problem. Ur sensor is seeing a lean code way before its going to see a rich code. So, there is air getting into somewhere. It could very well be the header cracked. Especially if its before the O2 sensor giving u that code. I would throw the original header back on. If that dont clear it up, maybe time to get a O2 simulator and that should just clear the issue. Oh, and you also tried the spark plug fouler mod. Pretty much it just takes the O2 out of the direct stream and somtimes kills codes. But I have no direct history with this. So look it up, it may help also. Goodluck.
Well, I finally got off my duff and found a cracked weld where the primary header tubes enter the collector. I had it welded today and stuck the scanner back into the vehicle. Well, the 02 sensor seems to be respopnding properly. However, welding the exhaust didn't completely fix the issue. I monitored my fuel trim data and o2 data and while scanning through all the live data, the scanner lost communications with the PCM, then suddenly came back up. When it does this though, the O2 sensor throwing the code is at 0 volts. I turn the car off and restart it, clear the codes and watch the data again. Again, the O2 responds as it is suppose to for a period before the data is briefly lost again, then coming back up with 0 volts on the O2. This cycle continues over and over again. I'm suspecting a wiring harness issue or a PCM issue. My wife is leaning on the harness based on the fact that the previous owner has replaced it once before due to having bottomed out the car and damaging the old harness as a result of lowering the car 2" in the front. I personally don't think I have ever bottomed out the car and damaged anything, and I don't see any physical indication of a damaged harness, however, that doesn't mean that their isn't any or hasn't been any damage as a result of me bottoming out the car. Any more inputs or thoughts would be appreciated.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
Well, it appears to finally be fixed.
I acquired the PCM schematics for power and grounds and for the engine sensors from a Chevy dealership. I did continuity checks from the O2 sensor causing the problems to the PCM connector and found no problems. I checks the grounds at the PCM for continuity to the battery negative terminal. Again, no problems. I checked the power supplies to the PCM and everything there was good too. I ordered a new PCM from Autozone and installed it about an hour ago, and drove the car stopping at the gas station, the parts store, and the grocery store. The CEL has not come back on yet. Through my experiences with this car, all this does not mean it is fixed. But if I were a technician, I would return it to the customer as fixed at this time.
I will drive the car for a week or so and post another update stating the condition of the CEL.
I want to tank all those that has given me input and suggestions. Some of the things I did in my quest to fix my problem couldn't have been done without your help.
And one last thing, if anyone would like copies of the wiring schematics I acquired from GM, I have them in PDF format and can e-mail them to you. Just shoot me an e-mail and I will get them to you withing a couple days. According to GM though, the schematics are specific to a 2002 J-body with a 2.4L "T" motor (LD9) with the Getrag 5-speed transmission.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
OK, so I was wrong. My O2 sensor wasn't plugged in. IU plugged it in and it threw a P0130. I cleared the code and started driving monitoring the O2 data. Everything appeared to operate and respond normally, then I noticed the CEL was back on. When I stopped to check and clear the codes, the P0171 was back, however the data that I was monitoring did not support that. Then, suddenly the scanner lost communications with the PCM for a brief minute. When the scanner came back up, the O2 sensor 1 data read 0 Volts. I cleared the codes and continued driving the car and the light never came back on, however the O2 sensor never read more than 0 Volts. I stopped and cycled the ignition and started driving again. The P0171 came back with the sensor reading what it is suppose to, then the scanner lost comms again. The cycle kept repeating over and over again.
I don't get it. I've replaced everything except the wiring harness that could possibly throw such code and yet it won't go away. I'm going ot replace the header and install it with new gaskets and hardware and see what happens then. If that doesn't work, I think I'm about ready to throw a match on this car, or sell it for what I paid for it. I just don't know. Any fresh ideas would certainly help. My third option is to pay the dealership to find and fix the problem.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
ever come up with a solution for this issue? I'm having the same code haunt me for over 2 years now and I've replaced just about everything
under the sun
01' Z24 5 speed
422whp/400wtq
T4 Turbocharged
Built LD9
HP Tuners
I know this is a late follow-up, but I sold the car for $800. I got tired of messing with it. However, the guy I sold it to had it investigated and fixed. The problem was in the steering column harness and was discovered by accident. I spoke with the shop owner when he came to me to get me to sign off on the title. There are some legalities in Virginia that protect me as a military member and the repairs of a vehicle titled to me. The guy I sold it to never transferred the title. Anyhow, the shop who fixed it had 2 different guys working on it. One was a skinny little guy and the other was a tall heavy set guy. By moving the steering tilt in the car, the short in the harness would come and go. One guy would have a light and the other would not. They replaced the harness with a new one and the problem went away. To me it sounds ridiculous, but it worked for them. So check out your steering column harness. You may have a rubbed wire causing your problem.
Some people have brain storms, others light drizzles. And then there are those that have droughts.
