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George H.
George H., ASE Certified Technician
Category: GM
Satisfied Customers: 18759
Experience:  15+years ASE Master W/L1 Drivability
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how do you reset the check engine light on a 2003 gmc yukon

Resolved Question:

how do you reset the check engine light on a 2003 gmc yukon xl?
Submitted: 7 years ago.
Category: GM
Expert:  George H. replied 7 years ago.

Hello I will help you with your question,


To clear the check engine light and keep it from returning the code that is stored in the computer will have to be pulled and the error or component corrected that was the cause of the light then a scantool is used to clear the code from the computer.


Do you have a code that needs to be diagnosed?



Customer: replied 7 years ago.

yes it came up with several codes





i have replaced the fuel filter and am wondering how i will know when the i have replaced the right part it has 93000 miles on it if that helps and runs great

Expert:  George H. replied 7 years ago.

These are lean mixture codes and a catalytic converter not performing code.


If the fuel pressure has not been checked yet that is where I would start and the mass air flow sensor is the first code so the reading from the MAF should be checked. The value that it is reading will depend on what scantool is used to read the sensor data.


If it runs fine the bank one catalyst is failing but on this truck these codes usually mean that the converter is clogged and it will have to be replaced in either case. The converters come as a set so you will be replacing both anyway.


Back to the MAF code. If you have a K&N filter the oil from the filter may have contaminated the sensor which will lead to the MAF, the lean codes but not the cat code


Let me know a little more about how the truck runs, the engine size and if you have any aftermarket parts installed.



Customer: replied 7 years ago.
no aftermarket parts the only problem we have had is in the am it idles very rough until it is warmed up, it has the 5.3 L engine. where is them MAF sensor and what reading should it have? how should i check the fuel pressure?
Expert:  George H. replied 7 years ago.

To check fuel pressure you will need a pressure gauge that some autoparts stores will sell/rent. Attach the pressure gauge to the service port on the fuel line and look for a reading of 55-62 PSI with the key on engine off then it should be 55 - 60 at idle and maintain that as you rev it to 2000 RPMs and hold it there for 30 seconds.


If the pressure drops below these readings the pump is failing. The port is on the crossover pipe, it has a screwon cap.


The MAF is in the air intake duct just beyond the air filter housing. If there are any air leaks between the MAF and the throttle body this can cause most of these codes. You will need a scantool to watch the MAF data at idle and at 2000 RPM. I will need to know what type of scantool you will monitior the MAF data with to see the values.


Here is some information about the MAF operation and the P0101 code


The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The powertrain control module (PCM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits:

  • An ignition 1 voltage circuit
  • A ground circuit
  • A signal circuit

The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies within a range of near 2,000 Hertz at idle to near 10,000 Hertz at maximum engine load. The PCM uses the following sensor inputs to calculate a predicted MAF value:

The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. If the PCM detects the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value DTC P0101 sets.


  • DTCs P0102, P0103, P0106, P0107, P0108, P0120, P0220, P0442, P0443, P0446, P0449, P0455, P0496, P2135 are not set.
  • The engine is cranking or running.
  • The ignition 1 signal is between 11-18 volts .
  • The throttle position (TP) indicated angle is less than 95 percent .
  • The change in the TP indicated angle is less than 5 percent .
  • The MAP sensor is more than 17 kPa .
  • The change in the MAP sensor is less than 3 kPa .
  • The above conditions are met for 1.5 seconds .

The PCM detects that the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value for more than 4 seconds .


  • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
  • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.


  • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Clear the MIL and the DTC with a scan tool.


  • Inspect the harness of the MAF sensor to verify that it is not routed too close to the following components:
  • The secondary ignition wires or coils
  • Any solenoids
  • Any relays
  • Any motors
  • A low minimum air rate through the sensor bore at idle or during deceleration may cause this DTC to set. Inspect for any vacuum leak downstream of the MAF sensor.
  • Inspect for any contamination or debris on the sensing elements of the MAF sensor.
  • Inspect the air induction system for any water intrusion. Any water that reaches the MAF sensor will skew the sensor and may cause this DTC to set.
  • A wide open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 3-10 g/s at idle to 170 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
  • A high resistance of 15 ohms or more on the ignition 1 voltage circuit may cause this DTC to set. A high resistance may cause a driveability concern before this DTC sets.
  • The barometric pressure (BARO) that is used to calculate the predicted mass air flow value is initially based on the MAP sensor at key ON. When the engine is running the BARO value is continually updated near wide open throttle. A skewed MAP sensor will cause the calculated mass air flow value to be inaccurate and may result in a no start condition. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 101 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude.
  • A high resistance on the 5-volt reference circuit of the MAP sensor may cause this DTC to set.
  • A high resistance on the low reference circuit of the MAP sensor may cause this DTC to set.
  • If the condition is intermittent, refer to Intermittent Conditions. See: Initial Inspection and Diagnostic Overview\Diagnostic Strategies\Intermittent Conditions

The maf is the component on the right in this diagram




Let m eknow what you have to test this with. The visual inspection of the MAF, checking for vacuum leaks and the fuel pressure testare the first tests that need to be done.


If you have a good scantool I can help you with some advanced testing, let me know





Customer: replied 7 years ago.
would i be able to rent a scantool at a local auto parts store also. i am driving this car on a 10 hour trip next weekend how bad would it be to drive if i cannot get fixed, i am thinking i may just have to take it to the shop. would the catalytic converter still be under warranty? i thought they last forever
Expert:  George H. replied 7 years ago.

The catalytic converters are under warranty for 8 yesrs/80,000 miles so if you fall within that the dealer will replace it if the truck comes in with the P0420 code and the cat has failed when they diagnose it.


A scantool that can see the MAF data, the fuel trims and the TPS/MAP data will cost at least $250 and the parts stores only pull the codes they don't diagnose the cause so they don't rent the tools for this. You might spend an hours worth of labor at a shop to have them diagnose the cause of the codes, it should not take them any longer than that.


If the truck is operated in a lean condition it can quit on you and engine damage can occur. I would try to get it repaired before your trip.


Let me know what I can do to help you with this


Thank you



Customer: replied 7 years ago.

the car has 91000 miles so the warranty is gone. any idea what the cost to replace the catalytic converter would be? if i fixed the other problems but not the catalytic converter would it still be bad to drive on the trip? money is tight .

Expert:  George H. replied 7 years ago.

If it is the cat they come in a set that is the exhaust from the manifolds to the "Y" and back to the rear single pipe.




The cost is about $500 and the labor to install it is 1.4 hours.



If the cat is not causing any drivability problems you will be fine leaving it until you can get around to repairing it. My concern was that I see these melted and restricting the exhaust. This will cause the lean codes and can cause the MAF code as well but you say the truck runs fine except for startup.


Sorry you are past the warranty, the engineers seem to hit the designed life right for the company most of the time.


Let me know if you have further questions about this


Thank you



Customer: replied 7 years ago.
thanks for the help if i have more questions can i email you again
Expert:  George H. replied 7 years ago.

When you login to the JA site you will see this question, post to it and I will respond as soon as I see it.


Let me know what you need and I will try to provide it.





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