My Tacoma seems to be running fine with no apparent issues but the CEL came on so I took it to both Autozone, then to Oreily for reading codes. Both places showed only one code: P0402. I took it to my Toyota dealer, they had codes P0100,P0110, and P0402. They reset CEL and insisted that if light comes back on then the MAF sensor ($1100) needs replaced. After about 80 miles it came back on. I decided to try cleaning the MAF sensor and reset CEL. Again, it came back on. I've heard that by disconnecting the MAF sensor while the engine is running and the engine shuts off, then the MAF sensor is ok, and doesn't need replaced. Is this true? I did this and my engine DOES shuts off immediately after disconnecting MAF snsor. I've also heard that a P0402 code usually means that the EGR valve is stuck open and the dpfe sensor is probably faulty and to test that first. I would hate to replace the expensive MAF sensor, only to find out the problem lies elsewhere. Any suggestions?
Thank you for writing you. You bring up several good points.
First, unplugging the mass airflow sensor doesn't always kill the engine. The engine's computer should go to a factory setting and try to calculate airflow with a default calibration to fuel intake. This will keep the engine running, but not running well. This is not the best test for the mass air flow sensor.
Secondly, the codes you have present are telling you the EGR, intake air temperature, and mass air flow sensor are outside of their normal readings. The best thing to do is to find out what these have in common. The EGR will depend on readings from the mass air flow sensor. The intake air temperature sensor is now part of the mass airflow sensor. All signs point to the mass airflow sensor.
Since cleaning it did not work, you will likely need to replace it. That is a steep price to pay at the dealership, and you will want to consider getting help elsewhere or doing the work yourself. The repair is what we call a "plug n' chug". This means all you do is take off the old part, put the new one in its place, and plug in the sensor.
If you are not feeling up to the work, you will want to check out prices at our MagicHands Certified locations near you.