QuestionHi there, my check engine light is on and I took it to a ahop. They gave me this codes. Can you help me out please? May I give you these codes and explain what I need to do to get this issues fixed? My first code is P0720. My 2nd code is P0171. My third code is P0446. Thank you so much. I greatly appreciate this.
AnswerHi, Candice. P0720 will likely be easier to fix than the other trouble codes. You can probably fix this problem yourself, but the others will likely require professional diagnosis by an experienced and knowledgeable driveability technician. Here's what they mean:
1. P0720 indicates that the transmission control module (TCM) is not receiving the proper signal from the transmission output speed sensor. Although I've seen problems with the vehicle speed sensor and its wiring as well as internal transmission problems cause this code in a few cases, the vast majority of times this code arises, it is due to a failure of the output speed sensor itself. I'd recommend replacing the sensor in this case, since it's very likely spending money on diagnostic work will lead to the same result.
2. For P0171, I'm first going to give you a short explanation of some of the workings of your fuel management system. Your engine control module (ECM) is preprogrammed with the amount of time an injector must be kept open under ideal conditions based on coolant temperature, throttle opening, and air flow readings. If we were able to operate the car under exactly ideal conditions, this would work very well. Unfortunately, we do not. So the ECM uses readings from the oxygen sensors to determine how it needs to adjust the opening time of the injectors to provide the proper air-fuel mixture. The percentage of adjustment is called fuel trim.
P0171 indicates that the fuel trim is a high enough positive number that the ECM believes there to be a problem. There are many potential causes for this:
-- fuel pressure may be low
-- the air flow sensor may be faulty
-- air may be entering the intake manifold without having to go through the air flow sensor (vacuum leak or leaking intake air hose)
-- an oxygen sensor may be faulty
-- there may be excessive alcohol in the fuel.
Without knowing the year and model of your vehicle, I cannot offer further advice as to common problems.
3. P0446 indicates vacuum is building in the fuel tank. This can be either due to a stuck open purge control valve or anything that can block the evaporative emissions system from sucking air into the tank as necessary to relieve the vacuum:
-- blockage of the air vent hose
-- stuck closed canister close valve
-- plugged canister filter
-- liquid fuel in charcoal canister.
