Diagnosing DTC P0171 (PI0552)

DIAGNOSING DTC P0171

TECHNICAL SERVICE BULLETIN

CONDITION/CONCERN

Some customers may comment that an SES light is on. Initial diagnosis may show that DTC P0171 has set.

This may be caused by the oil dipstick or oil fill cap not being properly seated as a result of maintenance work previously performed. To avoid this from happening, it is important to carefully install the oil fill cap so it is fully seated. It is equally important to seat the oil dipstick when checking oil levels.

RECOMMENDATION/INSTRUCTIONS

The small fuel efficient engines found in the Chevrolet Volt, Cruze and Sonic have a slightly different style oil fill cap than is found on other GM vehicles sold in the United States. This fill cap can sometimes be mis-installed and can cause an air leak. This air leak can also be caused by an unseated dipstick. Under normal engine operations, unfiltered air will be drawn into the engine and eventually set a P0171 code and an SES light. Service technicians need to make sure the cap and dipstick are full seated after an oil change is performed.

It may be difficult to know if the cap is fully engaged. A cap that is not fully seated could have a slight angle from the side view of the engine compared to a fully seated cap, which is flat from the side view of the engine. A cap that is seated at an angle is difficult to notice when looking at the top of the engine and may feel tight.

If DTC P0171 is set, current or in history, review the fuel trim readings.

• Long term fuel trim reading may show in the 19% to 35% range.
• Short term readings may vary from -20% to 36%.

Look at the oil dipstick and verify that it is fully seated. If not fully seated, reinstall the dipstick and observe the fuel trim readings.

• If the short term reading comes back to -6% to 6%, then the loose dipstick was the issue. Clear the codes and return the vehicle to the customer.
• If this does not make any difference, then inspect the oil fill cap.

Remove the cap and reinstall fully seating the cap in the cam cover and then observe the fuel trim readings.

• If the short term reading comes back to -6% to 6%, then the loose oil fill cap was the issue. Clear the codes and return the vehicle to the customer.
• If this does not make any difference, then further diagnosis needs to be performed according to Service Information for P0171.

In either case, it is not necessary to replace any parts. In most cases properly seating either the oil dipstick or the oil fill cap is all that is needed.