PO420, P0171 Need Help Please
PO420, P0171 Need Help Please
09-30-2010, 03:40 PM
When I looked up the P0420 and P0171 code it was leading me to a intake manifold gasket leak, bad fuel, bad 02 sensor, bad catalitic converter or a exhaust leak. I can't see any exhaust leak. So I cleared the codes to see what happens. Then the P0401 code sent me to clean the EGR valve. It was pretty bad. I would say at least a 50% blockage on the intake and exhaust side. I ran a entire can of carb cleaner through the intake port. I also cleaned the throttle body as it was pretty dirty. I have cleared the code again and I have put some Seafoam in the gas tank and filled it up with some high octane fuel.
My question is this, is there anyway that the P0401 code ( clogged EGR valve ) could have caused the P0420 and P0171 code? If not what else should I be looking for. I appreciate any and all help as my daughter needs this car to get back and forth from school and work.
10-01-2010, 04:08 AM
10-01-2010, 09:30 AM
Thanks for the quick reply. When I looked up the P420 and P0171 codes they gave this description.
PO420 Catalyst System Efficiency Below Threshold ( Bank one )
P0171 System to lean Bank One
But on the link you provided it pretty much said the P0171 was a dirty mass air flow sensor. But since both codes are pointing to a bank one issue I am not so sure it would be the mass air flow sensor as it doesn't have two different sides to separate a bank one and bank two codes. The dude at Oreily's said a dirty EGR could cause the engine to run real lean and cause both of the codes. Made sense to me, but again why would it only be on bank one?
I wonder why when I checked the codes yesterday both of those codes were gone and the only one there was P0401 code? This is what pointed me to the EGR valve.
I did some research on the first two codes and was reading where some people have ran a strong fuel system cleaner through the car and used a higher grade fuel and the codes went away. I never get off that easy, but I did at a bottle of Seafoam to the gas tank yesterday.
At this point I have cleared the codes and I will wait and see if the CEL comes on again and see what the codes are. My scanner software won't let me see the signal from the 02 sensors but if I get the P0420 code again I figure I would swap the upstream 02 sensors and see if the code switches to a bank two code. That would assure me that the 02 sensor is indeed bad. They are $60 each so I don't want to just throw parts at it. Plus they look like a pain to get to, probably have to soak them with PB Blaster for a couple days before I try and remove the 02 sensors. Let's hope I don't have to go there, lol!!
Another thing I noticed is it takes the Passport a couple hundred miles to set a code. The cars I have had before would usually set a code within 30 miles or so. Before this issue I had a code for the fuel tank pressure sensor. I could clear the code and it would stay off for a long time before it set the same code again. Like I said 150 to 200 miles. Is this normal for this car?
Like I said I really appreciate your help. If you can give me any other ideas to check I will do so. I may clean the mass air flow sensor. Is this sensor locates between the air box and the throttle body? There is a square aluminum block about 6-8" past the air filter box that the hose from the air filter slips over one side and another hose slips on the other side and goes to the throttle body. Inside there are thin strips of metal going across the width of the hose. IIRC there were three of them on the left side and a piece of aluminum running down the middle of it and it had two thin strips of metal on the right side?
10-01-2010, 05:35 PM
The dude at O'Reilly's is an idiot. A dirty EGR valve will not cause those codes. He's spouting off car speak trying to sound smart.
If the EGR valve system was clogged, or the valve was not opening, you would get a p0401. If the EGR valve was stuck open or partially open, you would get a p0402. The PCM can even sense if the EGR valve is not opening as much as the PCM is commanding it to open. There is a pintle position sensor built in to the valve.
The catalyst efficiency code is an indicator that your catalytic converter may be bad. The O2 sensor before the cat should put out a constantly fluctuating voltage. The one after the cat should be more steady. If the O2 after the cat is putting out a fluctuating voltage it will throw a code. Both codes could be a problem with bad O2 sensors but it could also indicate something else. If you want a definitive answer, you could take it in and pay a properly equipped shop to diagnose what is wrong. Then, you replace the parts yourself. The shop should have a high end scanner and a properly trained emissions specialist.
10-01-2010, 08:17 PM
Thanks again for the reply. I will wait and see what codes are present the next time the CEL comes on. I also learned that my software will allow me to monitor the O2 voltage, so if it sets the same codes I will check the voltage output of the Bank one O2 sensor. I haven't had time to check yet, but would bank one mean pass or drivers side?
Also is it normal for the codes to take so long to set a CEL light? I am use to codes resetting in 30 miles or less. But with this car is seems to take 150 to 200 miles to set.
Thanks again for all your help. I can't tell you how much I appreciate it. Any advice on changing the 02 sensors? I have never removed one and they seem to be the stock units. I was going to soak them down with PB Blaster for a couple days before I attempt removing them. This is if the codes reset themselves.
Have a great weekend.
10-03-2010, 12:52 PM
OK After I cleaned the EGR valve my daughter took the car on a 300 mile trip yesterday and the CEL light came back on. Here are the codes that were set.
P0171 system to lean bank one
P0172 system to rich bank one
P0174 system to lean bank two
P0175 system to rich bank two
I was able to read both of the upstream 02 sensors and they were varying in voltage from .05 to .875 and they were changing quite rapidly.
I was also able to read the voltage on the downstream 02 sensor and it was more steady maybe varying .2 to .3 volts and not nearly as rapid.
From what I understand it would seem that all three 02 sensors are working correctly.
What would cause the upstream sensors to read to lean and again to rich on both sides of the engine?
I did have her run a tank of high test gasoline and I put a can of Seafoam in the fuel to clean the fuel system.
The car seems to drive fine, but I really need to get this problem fixed. I would appreciate any help anyone could give me. So far I am thinking a bad MAF sensor, or IMG leak, or other vacuum leak. I will clean the MAF and I have looked for vacuum leaks but didn't find any.
10-03-2010, 03:02 PM
I would certainly start by getting some electronics cleaner and carefully cleaning the MAF element. Walmart sells it in a red can, called QD Electronics Cleaner. If that doesn't fix, replace the MAF.
10-03-2010, 04:38 PM
I have cleaned the Mass Air Flow sensor and cleared the codes. If they come back I will order a new one.
I can't tell you how much I appreciate the help.
10-06-2010, 01:42 PM
Okay, CEL is back on and I got the same P0171, P0172, P0174 and P0175 so I am going to go ahead and order a new Mass Air Flow Sensor.
But I also got a P1404 EGR stuck closed. I just took that thing apart and cleaned it. I will have to remove it and see if I can see anything wrong with it. Unless somebody has another idea?
Thanks for the help.
10-06-2010, 04:42 PM
"EGR stuck closed" is a different code than "EGR insufficient flow" in that the PCM can actually sense if the EGR valve has actually opened or not. If there was a clog in the passage, the PCM would be able to sense that the valve opened with no EGR flow. So, since you are getting the stuck closed code, the valve either will not open or the PCM cannot sense that it is opening. There is a little circuit board type potentiometer inside the EGR valve that will give a varied voltage output to the PCM depending on where the EGR pintle is. If that reading doesn't match up with what is expected, the PCM will throw a code. The likely problem is the EGR valve itself but the wiring could also be at fault.
10-06-2010, 05:53 PM
Yeah I figured as much. The pintel moves easily when I push on it so something may have gotten fried when I cleaned it last time. Anybody know where to get one at a decent price? Oreilly's wants $140 for a new EGR valve. I will probably sell it one I get it to stop setting codes. The middle cylinder on the pass side is leaking oil bad. I replaced all the plugs and that plug came out dripping oil. Not a good sign. To bad as my daughter really likes the car.
Thanks so much for your help on this forum Cat Fuzz. I got the new Mass air flow sensor in and I cleaned the EGR again just for the heck of it.
10-06-2010, 07:37 PM
the oil issue is the valve cover which has seals for the plugs. I've had one of mine replaced under warranty.
10-06-2010, 08:18 PM
the oil issue is the valve cover which has seals for the plugs. I've had one of mine replaced under warranty.
+1 on the valve cover seals. Easy fix, although, probably not under warranty anymore.
10-07-2010, 10:02 AM
Care to explain the procedure? The oil was on the bottom of the plug, not the top, I don't see how this could be from a valve cover gasket. More likely a bad ring seal or bad valve. But if you guys say it is that would be great. It was only the middle cylinder on passenger side. If I can fix this maybe I won't sell it, lol!!!
10-07-2010, 02:40 PM
I would consider a used EGR Valve at a salvage yard instead of $130.
10-07-2010, 02:56 PM
Don't have to many salvage yards around here. Plus at least with buying a new or rebuilt EGR I have a 12 month warranty. Go buy from the salvage yard and the warranty runs out before you get out of the parking lot.
I was reading another thread where some have run cheaper EGR's off some GM vehicles. They said the EGR looked identical and the plug was even the same, but I can't find the thread any longer and don't remember what model they got it from. I think it was a mid 80's or 90's Grand Am, but the part number was different too. I might as well just stick with the one the book calls for.
10-08-2010, 12:08 AM
The seal is near the top of the plug tube. The oil leaks down and puddles at the bottom of the plug tube. When you remove the plug, the puddled oil leaks down the threads and into the cylinder as it's coming out. If the oil was fresh and oily still, this is probably what's going on. Oil getting into the combustion chamber will usually burn off and leave gunky deposits on the plug, not oily oil.
10-08-2010, 09:05 AM
OK, maybe you are right. Yes the oil looked very fresh and dark black. I believe I know the rubber seal you are talking about. Is this the piece that the spark plug tube goes through and it sits just below the coil pack? Where can I get 6 of these? Maybe I will switch it with another cylinder and see if the oil residue dries up.
I sure appreciate the help. I was starting to think the motor was dusted.
10-08-2010, 02:55 PM
I was able to look at the Chiltons book today and I see the seal you are referring to. At least I think I do, it looks like it is actually under the valve cover and spark plug tube actually goes through it but it wasn't the one that is under the coil pack above. It looks like I need to pull the valve cover to get at those three. Is the valve cover gasket reuseable? Do these spark plug seals come with a valve cover gasket or can I get them separately? I guess I can find that out by calling the auto parts store. I am so thankful I found this forum and thank you for your time and sharing your knowledge. I thought this motor was soon to go. Maybe I will end up keeping her for awhile. My daughter really likes it. If I can keep the CEL light off it would be a win win. Thanks again.
10-08-2010, 11:51 PM
The spark plug tube seals come with a valve cover gasket set. You have to remove the valve cover to change them so you may as well install a new vc gasket while you're at it.
10-09-2010, 10:08 AM
Thanks Fuzz. That will be my next project. Doesn't appear to be to difficult. I am just waiting now to see if the EGR sets a code again. I am expecting it to.
I mentioned this before but is it normal for this engine to take 100-150 miles to set the CEL? My wifes highlander had a O2 sensor go bad and I would clear the code but it would reset the CEL before I ever got down to the street? Just curious if others have had these long times between CEL's.
10-10-2010, 12:26 AM
There are different times for each CEL code depending on what it is. For example, the PCM will not set a misfire code unless it detects a certain number of misfires within a specified time frame. Some fault codes require the PCM to see the fault more than once in a certain period of time before it will set a code. Sometimes a code will set right away, like a plugged EGR passage will throw a code as soon as you start driving but not at idle since the EGR valve is normally closed at idle.
10-12-2010, 02:21 PM
ok, finally got the new EGR valve on today. Before I cleared the codes I checked them again and the P0420 bank one is back along with the P0452. I feel like I am running around in circles. The p0452 is pointing back to the FTP sensor, which I already replaced a few weeks ago. The P0420 code is pointing to a bad converter or a bad 02 sensor. I have monitored both upstream 02 sensors and they both are switching between .1 and .9 volts fairly rapidly, so they appear to be working as planned. Like I said I put the new EGR valve in and cleared the codes. Will see what pops ups. I may end up getting a for sale sign for it. Thanks Cat Fuzz for all the help.
10-27-2010, 02:20 PM
Well the Mass Air Flow sensor and new EGR have cleared up some codes, but I am still getting the P0420 code and P0452 code. I have already changed the fuel pressure sensor above the fuel tank, so I don't know what else it could be?
I think I may also need a new converter. The 02 sensors are working as designed. I can see the upstream sensor flunctuating and the downstream sensor is more of a steady output. My scan is giving a description of the P0420 code as Catalyst System Efficiency Below Threshold Bank One. The freeze frame data for the P0420 code was this, Calculated load 9%, short term fuel trim bank one 0%, Short term fuel bank two 0%, Intake manifold Absolute pressure 13.3 in h.g
Coolant temp 180 F, Long term fuel trim bank one 3.12%, and long term fuel trim bank two 3.12%, engine rpm 834.
I didn't do a live data run today of the 02 sensors, but I remember when we got the P0420 code last time the Freeze Frame had a value for the short term fuel trim bank one and two and now it is giving me a zero for both. Not sure what this means? But I sure appreciate all the help y'all have given me especially Cat Fuzz.
10-28-2010, 12:54 AM
Actually, those fuel trim numbers are very good. 0% is actually ideal. This article does a pretty good job explaining.
The p0420 could still mean there is a problem with the catalyst on bank one. Even though you can see the upstream sensor switching and the downstream sensor staying flat, it may not be within spec enough to satisfy the PCM. The PCM's of OBD2 cars are pretty good at telling the difference between a bad cat and a bad O2 sensor. If the O2 was just slow switching, that would be another code entirely. If you wanted to find out for sure, there is a test that can be done but it requires a mechanic that is VERY well versed in emissions repairs. They can actually drill a hole in front of the cat and one behind the cat and get actual readings of the exhaust stream with a 4 or 5 gas analyzer and compare the before and after cat readings and tell you for sure if you need a new cat.
For the p0452 it could be a lot of things. A stuck open solenoid, a bad vacuum line, bad gas cap, etc. Check the easy stuff first, all the fuel evap lines, vacuum lines and maybe buy a new gas cap just for S&G's. If that turns up nothing, I'm afraid the next step is a smoke test, which is also a specialized emissions repair procedure requiring a pro equipped with the proper tools to perform.
10-28-2010, 08:42 AM
I can't remember right now but are there two cat's on the Passport? My daughter is at school so I can't verify, but I remember both sides going through a single cat. But I could be wrong. I can get a universal cat for around $100 and a sensor for $60. This would probably be cheaper than finding a place that has the equipment to perform these tests. I live in a small town so I would have to drive 45 min to the city to find a place. Could I swap the bank one and two sensors and if the code switches to low effiency bank two we would know it is the sensor and not the cat? Just a idea. I am leaving town for 10 days to 2 weeks so I will dive into this when I get back home. I can't thank you enough for all your help.
10-28-2010, 01:23 PM
Yeah, switching the O2 sensors around is a good way to eliminate the O2 sensors as a problem.
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