Hi, I purchased an OBD II scanner, and read a DTC(P0420). When I am reading the OBD manual, I don't know what is "pending code", and when and why it is there(under what condition it generates a pending code?)? I have cleared the DTC, but manual mentions that OBD 2 Drive cycle must be performed before resetting all the monitors, what is "OBD 2 Drive cycle"? If I just drive my car after clearing DTC, will the car do "OBD 2 Drive cycle" automatically? Thanks. WM
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Go ye to the source: http://www.obdii.com /
The answers you seek all are there.
The website doesn't have search functionality, I found info about "drive cycle", but I cannot find about "generating pending code". Hopefully, this can be answered here. Thanks.
Diagnostic Trouble Code ("DTC") P0420 means that the catalyst system efficiency for Bank 1 is operating below threshold.
In plain English, it means that the system thinks that the exhaust coming out of the catalytic converter is not clean enough. There are 2 possible causes for this trouble code: 1) the catalytic converter is not cleaning up the exhaust or 2) the O2 sensor that monitors the exhaust coming out of the catalytic converter is not measuring properly. My guess is that reason #2 is a more likely cause - the O2 sensor has gradually lost its effectiveness but is still sending a signal so the OBD system does not give an O2 sensor trouble code.
If you car is still covered by the emissions warranty (check your warranty booklet) then if the light comes on again, do not clear the code yourself. Let the code remain in memory and take it to a dealer for an emissions warranty repair.
Thanks Ray. I asked about P0420 before. I just want to understand why OBD II manual indicates that how OBD II scanner can detect a pending DTC and what does it mean? like potential problem on the way if it presents or some kind of alert functionality. Thanks.
Got answer from manufacture, thanks. "The tool will display pending codes. A pending code is a problem that the vehicle's computer has seen, but has not seen it enough to consider it a priority and turn on the MIL. "
I learned something new today!
If it was still covered by the emissions warranty, I would not reset the code, leave the check engine light illuminated, and take it to a dealer. If it was not covered by the emissions warranty, I'd clear the code and drive. If it come on again after that, check the indicated and related components.
The OBD II system does not detect or predict pending problems. It can only detect the presence or absence of problems.
To reduce false alarms, some problems need to be detected over the course of several trips before the check engine light (formally called a malfunction indicator light, or MIL) is illuminated and needs to not detect the problem of the course of several trips to extinguish the MIL. Toyota calls this 2 trip detection logic, and there are certain things that have to happen to count for a trip, like starting the engine cold, driving a certain number of miles over a certain speed, and engine coolant and O2 sensors reaching a certain temperature, so backing the car out of your garage will not be counted as a trip.
I don't know what brand scanner you have, but I'm guessing that the scanner manufacturer did not have a complete list of DTC's when they printed the manual, so if they didn't have the explanation of the codes, they were listed as pending DTC.
A certain number of OBD II diagnostic trouble codes are universal for all vehicles sold in North America (perhaps the world). You can use this site http://www.obdii.com/codes.html for a more complete list of codes.
Some OBD II trouble codes are specific to certain brands and would not be listed on the site a pasted above.
After reading your post, I am confused. I purchased Innova's OBD II scanner from walmart store. Here is their website:http://www.canobd2.com The device has three light indicators, green, yellow and red. In the user manual, there is a short description about "yellow LED" ? Yellow LED - indicates there is a possible problem. A "Pending" DTC is present and/or some of the vehicle's emission monitors have not run their diagnostic testing.
Wow! You spent $249 for a Scan tool? It is a nice tool with freeze frame capabilities but if you are not going to interpret actual sensor data output or if you automotive knowledge is limited, you can get away with a basic tool for under $100. For example, if you get voltage and cycle data from the #2 O2 sensor, would you know if the data indicates a good or a bad sensor?
Your explanation about the purpose of the yellow LED is different from the one I found on the site you referred to. http://www.canobd2.com/tool/quick_diagnose.asp On this page, it says that the yellow LED means possible problem / not ready for emissions test. The reason a vehicle might not be ready for an emissions test is that the system has not warmed up enough to go into "closed loop" mode. If you take the car for a 15 minute ride and then plug in the code reader, I'll bet you get a red light instead of a yellow light.
I suppose it is possible for a scan tool to detect a problem with 2-trip detection logic - that is, it found a problem with the first trip and is waiting for the second trip but in that scenario, the MIL would not be lit yet so you would not normally have a reason to pull codes.
Don't worry so much about the LED colors and focus on the actual code.
Thanks Ray. Actually I spent $69 on OBD 2, they have two models, the other one costs $100 at walmart. They are not the one advertised on their website.
IMO, most people should not buy more than a simple code reader unless they have a factory repair manual and know how to interpret actual sensor output readings.
But Ray, isn't that the same thing as predicting?...if it saw the same error several times in a row then it'll turn on the MIL, right?...so if it saw the same error maybe twice, then no error for another several trips then three more in a row...see my point?...isn't it 'predicting' a problem (sort of?)
I guess it's a matter of semantics. I was thinking of "predicting" as anticipating a problem before the problem actually occurs, and I was thinking of the 2 trip detection logic as double-checking.
On trouble codes that have 2 trip detection logic, I guess you could consider a problem with one trip, and the second trip has not occurred yet a "prediction" but that assumes that the problem will definitely occur on another trip. I gather that the OP's scan tool will illuminate a light showing that the ECU has stored a trouble code for 1 trip but not another trip yet so the MIL is not illuminated. The problem is, you normally would not scan for codes unless the MIL comes on, so unless you drive around with the scan tool connected, there is little benefit to "predicting" a trouble code.
Of course, right you are sir, thanks...
I've never heard of the "pending code" term before. To me, it is not a useful feature on a consumer oriented OBD II scanner.