2014 Chevrolet Sonic, 1.8L 4 CYL, Automatic
Problem: The customer’s concern was that the MIL
was on, the engine idled rough and there was a whistling noise
coming from under the hood.
Details: The technician pulled two DTCs: P0171
(Fuel trim system lean) and P2097 (Post catalyst fuel trim
system high limit). NOTE: P0171 sets when the ECM determines if
the fuel control system is in a lean condition, based on the
filtered long-term and short–term fuel trim metric. P2097
sets when the ECM determines if the post catalyst HO2S fuel
control system has been unable to adapt to a lean exhaust gas
condition for too long.
After reading about the same exact same problem in ALLDATA
Community, the tech performed the initial test outlined in the
post. First, he inspected the engine for any aftermarket
equipment or modifications related to the intake or exhaust
systems. Everything was original equipment and in good
shape. Next, he checked to see if vacuum was present at
the PCV orifice external port on the camshaft cover. There was
vacuum present. He sprayed carburetor cleaner on the camshaft
cover and the fuel trim instantly went negative. After removing
the cover, he noticed a crack in the cover.
Confirmed Repair: The technician replaced the
camshaft cover, cleared the codes and test-drove the vehicle.
The new camshaft cover fixed the problem. NOTE: This is a
common issue with these vehicles. We have also seen a cracked
intake boot located between the mass air flow sensor and the
intake manifold cause the same problem.