Can I convert it to a 4×4

ANSWER : Make sure that the truck is in park or neutral when shifting to 4×4 low. If it is, and you’re still getting this problem, you can try driving forward a bit to see if it engages in low gear. But there is more likely a problem with the transfer case or the switch. You should have the vehicle’s transmission scanned and diagnosed by a professional technician to ensure that the correct repairs are made.

ANSWER : Hi there, thanks for writing in. I am not sure why you changed your catalytic converter. Assuming you had a P0420 code, replacing the catalytic converter should of resolved that code. The codes originally stored need to be cleared. The fact your check engine light remains off tells me, you may have fixed the problem. Try disconnecting the negative battery terminal for at least 2 minutes, reconnect. Start and drive the vehicle for 10-15 miles. Re-check for codes. If a code returns on the first drive cycle (pending code), a problem still exists. The check engine light should come back on (the next drive cycle) if, the fault is recognized by the computer. An exhaust leak before the oxygen sensor will cause O2 sensor and catalytic converter codes. If you are having trouble identifying the fault, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.

ANSWER : This is likely a brake light switch problem. I would suggest testing the brake light switch which should be located down by the brake pedal. This may also be a computer problem as well as indicated by the other lights on in the dash. I would recommend having an expert from YourMechanic come to your home to possibly replace the brake light switch and diagnose with a scanning tool which will download useful data from the truck’s computer indicating what specifically the problem may be.

ANSWER : The obvious things you will need: Check if the transmission mounts are different. Verify bell housing bolt pattern to fit the engine. Replace the pedal assembly with one from an automatic. Shifter and linkage. Transmission cooler and lines. You can accomplish that by either swapping in the radiator from an automatic vehicle, or installing a larger transmission cooler in front of the radiator or a.c condenser if equipped. As for the transmission itself. If you are using a 3 speed like a C-6 transmission, then it should work fine with the vacuum signals. If you are looking to use a 4 speed automatic, then you need to do some research. Look for shops or companies that do performance building and modifications for transmissions. They may be able to make the 4 speed auto work without electronics. If not, there should be some stand-alone control unit options. Try some of the vehicle specific internet forums as well. Chances are there are others who have done what you are looking to do and can provide a wealth of information.

ANSWER : If the DPF filter is plugged up and the DPF light is on, then the DPF filter needs to be replaced. If you were to remove the filter and not use it, then the emissions output will be higher than normal and the DPF light will not go out. I recommend replacing the DPF filter, but if you are still having an issue, then I suggest replacing the catalytic converter system. If you need further assistance with your DPF light being on, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : Hello. The wrong converter will cause your check engine light to come on and will cause you to not pass emissions. It can also cause some performance and efficiency issues over time. There are specific converters built for all vehicles and that is what needs to be used, especially in California. You need to take it back to the shop that installed the wrong one as it is against emission regulations to install the wrong converter in California.

ANSWER : Hello – with the vehicle safely supported to provide clearance underneath – in between the engine oil and transmission pan, there is a large, funnel-shaped aluminum casting (called the bellhousing), that physically mounts the engine to the transmission. At the forward vertical face of the bellhousing (immediately behind the engine oil pan), is an access plate – remove it. The engine flywheel/flex plate is now exposed. There will be 3-4 bolts, which go through the flex plate to the torque converter, which hold the torque converter to the engine flywheel/flex plate. Turn the crank from the front crankshaft pulley bolt (CLOCKWISE facing the nose of the engine) a bit, remove a bolt, turn the crank a bit further, remove the next bolt, etc. until all the torque converter bolts are removed. At this point, you should be able to slide the torque converter toward the rear of the vehicle 1/4-1/2" by hand. This will confirm that all bolts are out. You will also be able to rotate the torque converter by hand, without turning the engine. Remember this when re-assembling the engine/transmission, and it becomes to rotate the torque converter to line up the bolt holes in the flex plate. Proceed with the removal of the transmission.

ANSWER : Hi there. The folks at CARB (California Air Resource Board) have set emissions standards for California sold vehicles for several years; which includes specific catalytic converter design. So if a mechanic is telling you that you require a specific catalytic converter for your vehicle, even if it’s not registered right now in California, it’s recommended to use that component; as it’s also adjusted for the ECU and other components on your Yukon.