P0172 – System too rich, bank 1
Last Updated 2015-12-17
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|Code||Fault Location||Probable Cause|
|P0172|| System too rich, bank 1 |
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|Intake blocked, EVAP canister purge valve, fuel pressure, EGR system, injector(s), HO2S|
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Table of Contents
- What Does Code P0172 Mean?
- What are the common causes of code P0172 ?
- What are the symptoms of code P0172 ?
- How do you troubleshoot code P0172 ?
- Codes Related to P0172
- Get Help with P0172
What Does Code P0172 Mean?
Your engine needs to put in the right amount of fuel for the amount of air coming into it, that is, the proper air-fuel ratio, to deliver the best power and fuel economy. The ECU (engine control unit) uses a number of sensors, such as the MAF, CKP, and ECT (mass air flow, crankshaft position, and engine coolant temperature) to determine how much fuel to put in. Using feedback from the HO2S, AFR (heated oxygen sensor or air-fuel-ratio sensor), or Lambda sensor, the ECU can fine-tune fuel injector pulse-width (IPW) to deliver the best air-fuel ratio.
As suggested by the names, the HO2S is sensitive to oxygen (O2) content in the exhaust, which has a direct relationship to air-fuel ratio. On combustion, some of the oxygen in the air is used to oxidize the fuel, leaving a small amount in the exhaust, which the HO2S measures, sending a signal back to the ECU.
If there is a lot of oxygen, this means that the engine is running lean, that is, not enough fuel was injected. Conversely, if there is very little oxygen, this means that the engine is running rich, that too much fuel was injected. Under normal operation, the ECU cycles between rich and lean air-fuel ratios, at the same time learning short-term fuel trim and long-term fuel trim (STFT and LTFT) values. Typically, fuel trims will be within 3% of the ideal, dependent on current air and coolant temperatures and load, for example.
On the other hand, engine problems, such as high fuel pressure, a skewed MAF signal, or a faulty fuel injector, may dump in more fuel than required, or misreport how much air is entering, resulting in a rich condition. The ECU will try to compensate, by reducing IPW, but if fuel trim goes over -25% or so, the ECU interprets this as a malfunction, setting a DTC (diagnostic trouble code), DTC P0172 – Fuel System Too Rich (Bank 1), and illuminating the MIL or CEL (malfunction indicator lamp or check-engine light).
What are the common causes of code P0172 ?
Depending on year, make, and model, DTC P0172 may have number of causes. Here are some of the most common.
- Toyota / Lexus – Contaminated MAF, usually with aftermarket filters. The reasons for this correlation aren’t clear, but many Toyota hotwire MAFs are particularly susceptible to contamination. Cleaning isn’t usually successful. Discard the old MAF and engine air filter. Clean the air box and install the new MAF and air filter, preferably using OEM parts, making sure that the air box seals properly.
- Oiled Filters – Some engines with a lot of blow-by, whether by design or age, and may allow oil into the air box, and subsequently, the air filter and MAF. Also, some aftermarket air filters require oil treatment for proper operation, which some owners may be overzealous in applying. In either case, excessive oil can contaminate the MAF, leading to skewed air flow measurements. Also, check that the PCV and tubing are in proper working order.
- Dirt – In an ideal world, your engine bay would be spotless. Over time, however, dirt and grime builds up, and it can easily find its way into the engine and control systems. Older and neglected vehicles can easily suffer MAF contamination, for excessive dust and dirt or a poorly-sealed air box.
- Leaking Fuel Injector – Age or contamination may cause a fuel injector to leak, dumping fuel into the cylinder even when not commanded. Check the oil for fuel smell, which is a good indicator of fuel leakage.
- Leaking Fuel Pressure Regulator – Some vehicles, with vacuum-operated fuel pressure regulators, have been known to leak internally, passing unmetered fuel directly into the intake.
What are the symptoms of code P0172 ?
Depending on the nature of the failure, DTC P0172 may or may not be accompanied by drivability issues. At the very least, you will experience poor fuel economy, because, with the ECU in “limp-home mode,” it is no longer looking at HO2S and AFR sensors for feedback.
On the opposite end of the scale, you may note rough idling, lack of power on acceleration, even misfiring or stalling, which tends to get progressively worse as the engine warms up. Particularly bad cases may be accompanied by black exhaust smoke and a blinking MIL, alerting you to possible catalytic converter damage. You may also smell a strong fuel odor and see black soot in the exhaust tip or the back of the car, an indicator that a lot of unburnt fuel is making it through the system.
How do you troubleshoot code P0172 ?
Pro Tip: Before diagnosing fuel trim problems, it does one well to note that the Fuel Trim Monitor will not run unless the HO2S monitors have run and passed first. The fuel trim monitor uses the oxygen sensor to run, which means that fuel trim codes are not oxygen sensor codes.
- P0172 with P0175 or MAF DTCs – If you note both P0172 and P0175 or concurrent MAF-related DTCs, then you can likely rule out individual cylinder, ignition, and fuel injector problems. Instead, focus on the fuel injection system and the MAF.
- MAF contamination could skew air intake measurements, therefore skewing fuel injection calculations. Cleaning may solve the problem. replacement, along with a new air filter and properly sealed air box, would be a more permanent solution.
- Check fuel pressure, making sure that it is within the proper range. Excess pressure, such as caused by a defective pressure regulator or pinched return line, would result in more fuel being injected than the ECU is expecting.
- Verify proper ECT and IAT (intake air temperature) readings. The ECU may or may not pick up on stuck sensors, so it does one good to check that ECT and IAT are in normal ranges. For example, if you’ve been running the engine for half-an-hour on a hot day, the ECT should read at least 175 °F. If it still reads 32 °F, the ECU will enrich AFR to compensate, resulting in a rich condition.
- P0172 with other Bank 1 DTCs – If you note only P0172, maybe concurrent Bank 1 DTCs, such as a cylinder misfire, focus your attention on Bank 1.
- Fuel Pressure Drop – With the engine running, record fuel pressure, then shut the engine off. Fuel pressure may drop slightly, but should remain stable for at least 10 or 15 minutes. If the fuel pressure continues to drop, you could have a leaking fuel injector, which would lead to a rich condition and possible misfire condition.
- Cylinder Misfire – A misfiring cylinder would dump unburnt fuel into the exhaust stream. Diagnose and repair a cylinder misfire before attempting to diagnose a rich condition. Pay attention to concurrent DTCs, such as those pertaining to VVT (variable valve timing) or the ignition system.
- Exhaust – Check the exhaust for leaks between the cylinder head and oxygen sensor. While the exhaust system seems like a positive-pressure system, air can enter in the partial vacuum created by the exhaust pressure pulses. Atmospheric oxygen entering before the HO2S would skew oxygen content measurements.
Codes Related to P0172
While diagnosing DTC P0172, you may also run across these other DTCs:
- P0170 – Fuel Trim Malfunction (Bank 1)
- P0173 – Fuel Trim Malfunction (Bank 2)
- P0175 – Fuel System Too Rich (Bank 2)
- P0101 – Mass Air Flow Circuit Range / Performance
- P0104 – Mass Air Flow Circuit Intermittent
- P030x – Cylinder Misfire Random or Specific
Along the same lines, but on the opposite end of the scale, other fuel system DTCs may include:
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I have a 2009 Hyundai accent 1.6l l4.
I replace the coil packs back in December but they went out a month later I had to replace those as well. I replace my catalytic converter because I was shooting a cold and when I took it off it was like a rock inside. After replacing it I reset the codes but the car is still accelerating horribly. I will approach the hill going 40 and then without pressing any more gas or less it will go down to 20. In the morning when I first start it accelerates great and then after about minute it accelerates horribly. Austin also when driving I have to get it up to 3500 or 3000 RPM to switch gears. I know it’s not the transmission it just seems like there’s too much spinning going on somewhere. Somebody tells me a fuel pump somebody else tells me maybe my mass air flow sensor. And only have about 300 work with doing my own labor
I think we need more background information regarding your vehicle history: list of DTCs, current mileage, previous repairs, etc. I’m guessing that you’re posting in the P0172 discussion because you have this code. Are there any others? If the engine is running rough, that would indicate a misfire, the excess unburnt fuel and oxygen throwing off the fuel trim readings. I think I would start with checking the spark plugs, perhaps doing a compression test, and a fuel pressure test.
My research indicates that coil packs are a major problem on this engine, which it seems that you replaced, but why did you replace the ignition coils, and then again a month later? Did the first coil-pack replacement fix the problem, even if only temporarily? Is the coil pack wire harness in good condition? Are you using factory coil packs? Are you using stock spark plugs gapped to 0.035″?
It seems like you replaced the catalytic converter because it was broken inside, is that correct? (I don’t think that has anything to do with your problem, however.)
2 codes constant, P0172 and PO299, and will not pass smog, what can be the problem?
Code defaut p0172 et p0300
P0172 P0175 problems
my 2006 Dodge Ram 1500 is putting out P0172 & P0175 codes. I took it to the repair shop, Arden High Tech Auto Repair, and was told that I needed to either get a valve job or used engine replacement. Note, my vehicle was not running rough, misfiring, or stalling, etc… I went with the engine replacement, as my truck had over 200K miles. When I got the truck back it STILL has the codes! All sensors have been replaced, the injectors are new, and the exhaust and manifold gaskets were replaced… It is at another shop for over a week now, and the only thing that they can say so far is that it is NOT a mechanical issue… What am I or they, missing?
They’re right its probably not a mechanical issue. Hello Angela. While forking out money to find the problem, these shops are trying every possible thing it could be. One thing that does comes to mind is taking a look at the evap system for problems, and the (T.i.p.m.) or the totally integrated power module. It is basically the central microprocessor for the entire car. It can cause the 4wd to act up,the fuel pump to not kick on, and many many issues. if an evap component were going bad, this code would make sense. Also, like I mentioned before, have someone troubleshoot the tipm. Good luck, and hope you get it fixed.
I have a hyundai avante when filling the fuel tank when the engine is running it only responds by stepping on the accelerator pedal and on the way there is a slowdown, code p0172 p0420
Hello Muftah. The problem can be a plugged, or burnt catalytic converter, it can also cause it to loose power during acceleration. A Back pressure test can tell you if it is bad or not. The catalytic converter can also cause the lean code. (P0172). Some carbon may have built up on the 02 sensor resulting from this. Good luck.
Hi all. I am new here.
My 2008 VW Jetta was hard to start especially in the morning or when let sit for more than 2 hours. I suspected it was the fuel pump and I did replace it. Fortunately, the fuel pump replacement fixed the problem however, since the replacement the check engine light keeps coming ON. When I checked for codes, I got the P0172.
IS it possible that the fuel pump could be the culprit since this was the last repair I made to the car?
Hi Ben, I have a 2015 citroen ds5 with ep6 thp 1.6, check engine light is on and P0172 code, the engine runs well its only in the morning when start the car it runs rough for about 10 seconds then it becomes normal, do you have any idea what can it be? Thanks in advance…
Hello Zed. With the engine running rich and rough for the first 10 minutes like you described, the 02 sensors or m.a.p sensor would be a big culprit. Also, if it goes away it sounds like the ful trim is compensating to make it adapt and run better after that. So the fuel pressure regulator would be a good idea to check. Cheers and good luck.
Hola solo tengo p0172 en una camioneta ford motor 4.6l, tiembla un poco
my terrain intermittently gives P1072 code. Of course it never happens when I can actually check anything. Any suggestions as to what could cause intermittent issues. I feel like the O2 sensor would always be bad, as well as Dirty MAF.
Are there any other codes that coincide with the one stated? If not I would check for over fueling on that side. Check for open injectors that could be causing gas to dump in the cylinder and causing it to run rich. Most of the time you can get an inferred temp gun for $40 and shoot the temp on the exhaust ports and the cooler the cylinder that is the one that is pouring to.much fuel and causing the engine to run rough. It will tell you whether or not its an injector issue or if u have an issue else where. If you need to reach out shoot me an email and I will get you some more info or try and get video with some diag steps and info.
Warm greetings from Florida! I have my 2010 Volvo S80 T6 (3.0 turbo) 84k miles on odometer, throwing P0172 code, it runs fine but I know for a fact that the fuel pump is starting to fail due to long cranking time when start. This has been happening for the last 6-7 months but since either me or my wife barely use this car I’ve decided to wait longer to replace the pump. What’s new is the code P0172, came on 2 days ago and is the first time I see a code in this car. I have also noticed in the last year a whistle sound coming from the turbo BOV even under normal acceleration and between shifts, it’s becoming more noticeable every time and although is a cool turbo whistle very desirable I’m suspecting the rubber diaphragm in the BOV is ripping off. Would any of these 2 issues be causing this code popping up? If this is the case I will finally address them once for all. Thanks in advance and Happy New Year!!!
I have a Toyota crown 2jz fse engine which is running rich, p0172. I recently cleaned the injectors as I thought they were the cause of the engine running rich. Previously it was throwing p0172 and p0175 before cleaning them.
The oxygen sensor on bank 1 is also behaving abnormally as it’s consistently staying at 1v.
I have a 2012 Mini Cooper S R56 that currently has the check engine light on with code P0172 (showing as permanent). So far I have had the high pressure fuel pump replaced, the air intake box, the thermostat/thermostat housing, valve cover gasket (due to leakage during a smoke test), all 4 spark plugs, and both O2 sensors. I have cleaned the MAF with CRC MAF cleaner as well. Even with all of this I have had the light continuously come back on even after clearing all codes. The other codes that tend to pop up along with the P0172 are P0300 (random misfires detected, and those have been on cylinders 1,3 and 4). I had a mechanic look at the cylinders and he said they look good. Also I am not noticing any drastic fuel consumption issues as I can fill up and not have to do so again for 2 weeks (average 26.8 miles a gallon). I have noticed over time black soot on my exhaust as this problem has been going on for the last 6 months. The only things I have left to try are checking all the hoses for a vacuum leak, and possibly replacing the MAF and or cylinders. I am just looking for some advice regarding this issue.
Hi Joel: Reposted to BAT for responses: http://www.batauto.com/threads/2012-mini-cooper-s-r56-check-engine-p0172.15266/
Hi all, i have mercury grand marquis 2002 Ls. The problem is that i have replaced all 4 of my O2 (oxygen) sensors but still i am getting codes P0172, P1152. My car easily goes to 100 mph no issues in power but sometimes the car jerks when i lift my foot of the gas paddle. I have new spark plugs, coils are good but still it also sometimes show cylinder 6 misfire. Please help me!
I have a Peugeot 308 with ep6dt engine and a P0172 fault code. Rough idle, stalling etc. What do you suggest.