Was your engine service light reset at the last oil change? If not this is the cause. The manual is incorrect in the resetting procedure. If the service tech thinks he reset it as per the manual it was not done. The correct pumps on the accelerator pedal is 3 not 2 as indicated in the manual.
FYI below is from the manual
Engine Oil Life System
When to Change Engine Oil
Your vehicle has a computer system that lets you know
when to change the engine oil and filter. This is
based on engine revolutions and engine temperature,
and not on mileage. Based on driving conditions,
the mileage at which an oil change will be indicated can
vary considerably. For the oil life system to work
properly, you must reset the system every time the oil is
When the system has calculated that oil life has been
diminished, it will indicate that an oil change is
necessary. A Service Engine Oil light on the trip
computer display will come on. See Trip Computer on
page 3-33. Change engine oil as soon as possible within
the next 600 miles (1 000 km). It is possible that, if
you are driving under the best conditions, the oil
life system may not indicate that an oil change is
necessary for over a year. However, the engine oil and
filter must be changed at least once a year and at
this time the system must be reset. Your dealer has
GM-trained service people who will perform this
work using genuine GM parts and reset the system. It is
also important to check engine oil regularly and keep
it at the proper level.
How to Reset the Engine Oil Life System
The Engine Oil Life System calculates when to change
the engine oil and filter based on vehicle use. Anytime
engine oil is changed, reset the system so it can
calculate when the next oil change is required. If a
situation occurs where you change your oil prior to
the Service Engine Oil light being turned on, reset
1. With the engine off, turn the ignition key to ON.
2. Fully press and release the accelerator pedal slowly
two times within five seconds. (DO THIS 3 TIMES NOT 2)
3. Turn the key to LOCK.
If the Service Engine Oil light comes back on when
you start your vehicle, the engine oil life system
has not reset. Repeat the procedure.