2 codes- P0101 & P0641 where should i start

SOURCE: oil pressure high

could be oil pressure switch in eng block ??engine light on? if so scan it for fault codes retreve and start looking for dealer explanation perhaps

SOURCE: Engine light -Code P2901 read on Genisys scan tool

DTC P2501
Generator L-Terminal Circuit High Voltage
Maybe it was this one?

Dave C

• 1050 Answers
• Posted on May 14, 2009

SOURCE: 02 sensors not ready

The code P0420 indicates that the catalytic converter is not functioning efficiently. This could be because the cat is damaged or the engine is not running very well and the cat cannot keep up with the emissions. You should ensure that the spark plugs and ignition components are in top shape before replacing anything else. If a compression check reveals a low cylinder, you will not be able to prevent this code as even a new cat cannot keep up with a dead miss. If the state of tune and the compression is good, then you'll likely need a cat.

I've posted the drive cycle just so you know what to do when you have resolved the code.

1. Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup.
   Do not leave the key in prior to the cold start or the heated oxygen sensor diagnostic may not run.
   
2. Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire, and - if closed loop is achieved- Fuel Trim.
   
3. Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
   
4. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
   
5. Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
   
6. Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.
   
7. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
   
8. Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

SOURCE: 2003 GMC Envoy - High Oil Pressure Reading

Sounds like an oil pressure sensor. Here is a diagram to locate it for removal. Best of luck.
Greg

http://www.chiltonlibrary.com/content/images/21202/images/21202_GDIA_g518.pdf

SOURCE: P0101 p0171 p0174 engine codes

Those are lean codes and a MAF (P0101) code. Make sure the MAF sensor is plugged in, and there are no leaks/ loose hoses between the air filter and the engine. You may have a vac leak at the intake also, but check these first, If all appears OK a repair shop will need to check it out for you.