Originally Posted by starlet119
Anybody have an issue with the battery not charging and getting faults 21 and 31, my car is in limp mode and the battery dies while running.
Battery not charging could be multiple things Including the batter itself is bad or the alternator is bad/not charging. To seperate the two of theses problems get a Volt meter and put the positive lead of the meter on the positive battery post and negative of meter to batt negative post. With the car running, have somebody bring the gas up to 2500 Rpms with no load on the charging system (no lights, radio, ac, wipers) turn on, the volt meter should read between 13.9 to 14.5 V depending on the alternator. With loads on the system, (wipers, radio, flashers, lights, Ac, and window defrost) turn on @ 2500 Rpms you should see at least 13.0 to 14.0 V. if these are the readings you are getting, that shows that alternator is fine leaving you to just your battery. Now, if you have a way of confirming the battery is good "which is something you should do first" and you are not getting these readings, then you have other electrical problems. A bad batter will throw off the test results so make sure the batter is good and fully charged.
DTC 31 is for the Mass air flow sensor which is definitely why the car is in Limp mode. Cuz if your ecu is missing a signal from the meter the car will run like ****. The sensor could be bad, dirty, reading false air or something. Check the MAF sensor. DTC 21 is an O2 sensor code. Again, sensor could be mad, or have damages wires or possibly isn't plug in. These are things you need to check. Post your results if u still need help after this.