How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Michael Moore Your Own Question
Michael Moore
Category: Chevy
Satisfied Customers: 2956
Experience:  ASE Master/GM WORLD CLASS/GM Master/GM ASEP/Dodge Gold/Mazda cert.
Type Your Chevy Question Here...
Michael Moore is online now
A new question is answered every 9 seconds

I have a 2000 Chevy Blazer S-10. The Service Engine Soon light

Resolved Question:

I have a 2000 Chevy Blazer S-10. The Service Engine Soon light keeps coming on. Two sensors have been changed but, it still happens. It seems to happen only when I fill the tank up. It'll come on then go off and stay off till I fill it up again. Do I need a new gas cap? After putting the new cap on, should I disconnect the battery to reset the computer?
Submitted: 8 years ago via
Category: Chevy
Expert:  Michael Moore replied 8 years ago.
Do you know what codes are setting??
Customer: replied 8 years ago.
No, I saw the codes but, I forget what they were but, according to the mechanic, it was for the oxygen sensor. After changing one it came on again and he changed a different one. Now it still comes on, like I said, seems only to do this after filling the tank.
Expert:  Michael Moore replied 8 years ago.
The engine light may be comming on for a differant concern. You need to find out what codes are setting, you can go to your local auto parts store, most of them will read the codes for free. You need to write down what code numbers are setting such as p0300 p0133. Unless we know what codes are set, there is no way to perform a diagnosis. Let me know if you can get the codes.
Customer: replied 8 years ago.

I don't think I have the codes written down anywhere and if I have to get them I might as well have the mechanic that gets me the code fix it, shouldn't I? I just thought that maybe a new gas cap would solve the problem since it happens when I fill the tank. Thanks anyway.


Expert:  Michael Moore replied 8 years ago.

If you want to take it back to them, find out the codes and make sure they write it down so if the light does come back on, and it sets the same code then they should not be charging you again for the repair. If you have some paper work for the repairs thay have made already, then the codes should be written down as part of there stroy for the repair.

If the gas cap was bad, the light should stay on all the time and not go off when you put in gas. You might just want to replace the cap and see what happens, the caps are cheap and you can get them at any auto store, just stay away from the locking caps, they cause more problems with check engine lights. It may be a fuel level sensor that is going bad inside of the tank, this will set a p0463 code and may clear up when fuel is added.

Let me know if you find ou any code information.

Customer: replied 8 years ago.
when fuel is added to the sensor itself? Is it easy to change this sensor if need be? Thanks for the advise on the locking caps. I was thinking that if I should replace it I would get one but, I will take your should know. If I change the cap, should I go ahead and disconnect the battery and re-connect it to reset the computer?
Expert:  Michael Moore replied 8 years ago.

The fuel level sensor is inside of the fuel tank, this is the sensor that tells your fuel gage how much fuel is in the tank. If you are having fuel gage problems then the sensor is bad. If not, there maybe something else wrong. The fuel level sensorneeds to be replaced by someone that has at least light car repair skills since the fuel tank needs to be removed.

Disconecting the battery will not clear the codes on most cars, if you go to a auto parts store, they can clear the codes for you for free, I would have them write the codes down before they clear them, this way you know what codes are setting if the light comes back on.

Customer: replied 8 years ago.
Why would filling the tank set this sensor off? Why does the light go off if it is some malfunctioned part?
Expert:  Michael Moore replied 8 years ago.

If there is a bad spot on the sensor, lets say when the fuel level gets to 1/4 full, the snesor may have a open circuit, when you fill the tank, the sensor moves due to the float in the tank, this then makes the sensor read correctly again. The reason this will set off a check engine light is due to the engine computer performs a evap leak test for the fuel system (the computer checks for leaks in the fuel tank such as the fuel cap). The computer can only run this test when the fuel level is between 3/4 and 1/4 full. If the fuel level sensor is going bad, then te engine computer does not know how much fuel is really in te tank which can affect the test results.


This is only a possiblity and unless the code P0463 is set, then this is only a guess.


DTC P0463 Fuel Level Sensor Circuit High Voltage

Circuit Description

The vehicle control module (VCM) requires an accurate indication of fuel level for evaporative emission (EVAP) system diagnosis. The fuel level in the fuel tank changes the rate of vacuum decay for the EVAP system leak DTCs.

The fuel level sensor changes resistance based on fuel level. The fuel level sensor has a signal circuit and a ground circuit. The VCM applies a voltage of about 5 volts on the signal circuit to the sensor. The VCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine fuel level.

When the fuel tank is full, the sensor resistance is high, and the VCMs signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the VCM will sense a high signal voltage (fuel tank full). When the fuel tank is empty, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the VCM to sense a low signal voltage (fuel tank empty).

The VCM uses the input from the fuel level sensor to calculate the fuel level in the fuel tank. This information is then sent to the IPC through Serial Data.

The diagnostic will not run when the tank is more than 85 percent or less than 15 percent full. (This sensor signal disables the misfire when the fuel levels are less than 15 percent).




Customer: replied 8 years ago.
Okay, now if this IS the case, then why would the code come back as an oxygen sensor? I saw the code and I saw what was written in the mechanic's code book. I don't mean to be a pain, it's just that I'm widowed and everytime something goes wrong with the car I feel like the mecanics are taking me for a ride. I figure if I ask enough questions then I will be able to talk to them more intelligently. I really do appreciate all this information.
Expert:  Michael Moore replied 8 years ago.

If there were oxygen sensor codes, then the fuel level sensor is most likely not the problem. Oxygen sensor codes can be caused by many things, from a leak in the exhaust system, bad wire, blown fuse, improper fuel, engine that runs rich or lean just to name a few.

I have seen oxygen sensor problems that are set by a bad oxygen sensor and was replaced with a aftermarket sensor, only to reset the code. Aftermarket oxygen sensors are a unviresal fit, not a direct replacement. Only GM has the direct replacement sensor and should be used for best performace. They cost a little more but for a good reason.


Let me know if you need more info, I'am here to help.

Michael Moore and other Chevy Specialists are ready to help you
Customer: replied 8 years ago.
okay, thank you