First lets clear up some misinformation. Getting stuck in second gear, assuming you have an automatic transmission, is "limp mode". That occurs when the transmission computer detects a problem. That can be a sensor circuit problem or a mechanical problem that was detected through the sensors' data. Regardless whether it goes to limp mode or not, a diagnostic fault code will be set, but those codes never say to replace a part or that one is bad. Fault codes only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition.
The people at most auto parts stores will read the fault codes for you for free, but most of the time they never were mechanics. They understand selling parts, not diagnosing the causes of problems. Too many customers think we just read the codes and know which part to replace. When a part is referenced in a fault code, it is actually the cause of that code about half of the time. Before we waste your money on an unneeded part, we have to rule out wiring and electrical connector terminal problems, and mechanical problems related to that part. A majority of fault codes don't even make reference to a part, such as, "running lean too long", "cylinder four balance fault".
To add to the misery, the code readers used by most auto parts stores only read fault codes in the engine computers. Typically you will get code P700 which just means there are codes in the transmission computer that need to be read and recorded. Most simple code readers cannot access transmission computers, body computers, airbag computers, ABS computers, or the dozens of other computers. For those, you usually need to visit a mechanic who has a scanner that can access all the computers.
Once you have the codes read in the transmission computer, you need to know the exact code number. Some code readers provide a description of the code, but those vary between code reader manufacturers and are often open to interpretation. Do not rely on those descriptions to tell you to buy a part. For example, as my students learned from working on my "bugged" cars, "Throttle position sensor voltage low" is rarely caused by a defective throttle position sensor. The solution almost always involves spending some time finding the cause, and no dollars for parts to fix it.
Once you know the code numbers, you can go here to find the definitions:
https://www.2carpros.com/trouble_codes/obd2
or you can include it in your reply and I will interpret it for you. Some codes are manufacturer-specific and differ from what is on this list. For those, we need to go to a service manual for your vehicle. If we need to look at a wiring diagram, you will need to list the correct engine size. The diagrams and parts used vary quite a bit depending on which optional engine size you have.
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Monday, December 18th, 2017 AT 3:07 PM
