SES Light Is On With DTCs P0171 and/or P0174 Set – 2012-2019 Buick Cadillac Chevrolet GMC

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Bulletin No.: PIP5549A Published date: 05/7/2019

Preliminary Information

PIP5549A Diagnostic Tip – SES Light Is On With DTCs P0171 and/or P0174 Set

Models

Brand: Model: Model Years:

VIN:

from to

Engine: Transmissions:

Buick Enclave 2012 – 2019 All All 3.6 LLT,
3.6LFY All Cadillac XTS 2015 – 2019 All
All 3.6 LFX All Chevrolet Colorado 2015 –
2016 All All 3.6 LFX All Chevrolet
Equinox 2015 – 2017 All All 3..6 LFX
All Chevrolet Impala 2015 – 2019 All All 3.6
LFX All Chevrolet Traverse 2012 – 2019
All All 3.6 LFX, 3.6 LFY All GMC Acadia
2012 – 2017 All All 3.6 LLT All GMC
Canyon 2015 – 2016 All All 3.6 LFX
All GMC Terrain 2015 – 2017 All All
3.6 LFX All

Involved Region or Country North America

A customer may bring their vehicle to the dealer with a complaint of an SES light on.

Condition

Upon diagnosis the technician may find DTC’s P0171 and/or P0174 stored in the ECM.

Cause Possible Vacuum leak in intake or Purge.

Correction:

1. Ensure vehicle is at operating temperature then monitor and record Long Term & Short Term fuel
trims. Plug both the manifold hole and the disconnected foul air tube hole.

2. Shut the engine off and disconnect the foul air tube from the intake manifold.

Detach foul air tube from connection shown above at arrow 1 and plug both sides

3. Restart the vehicle and monitor the Short Term & Long Term fuel trims.

Results:

1. If both the previously recorded Long term and Short term fuel trims were at a positive value
above 5 and now the Short term has gone to a consistent negative value during this test replace the
foul air tube.

2. If the previously recorded Short term is at a value above positive 5 and the long term is
between -2 and 2, but during the test the short term has gone to a zero or negative value replace
the foul air tube.

3. If the fuel trims in steps 1 or 2 did not change proceed with purge valve test.

Note: In some cases the Intake Manifold may have to be replaced if foul air tube replacement by
itself doesn’t address the vacuum leak.

Only replace manifold if test above impacted fuel trims.

Purge Valve Test

If during the test procedure outlined above the fuel trims didn’t change after foul air tube was
capped off proceed to the following test.

1. Shut the vehicle off and ensure the foul air tube and manifold plugs have been removed and
re-install the foul air tube to the manifold

2. Locate the purge valve on the intake manifold (see below)

3. Disconnect vacuum hose and power supply from purge valve (see below)

4. Restart the vehicle then place your finger or a vacuum gauge over the open port on the purge
valve.

5. If you feel vacuum or read vacuum on the gauge at the port of the valve it will need to be
replaced. Shut the vehicle off and then re-install detached components

1. If no vacuum was felt or measured at purge valve port refer to the applicable DTC in service
information to diagnose further.

NOTE: When a permanent repair or part replacement is identified a PI revision or bulletin will be
submitted.

Warranty Information

For vehicles repaired under warranty, use the current labor time for the actual repair made.

Version History

Version 2

Modified 01/23/2018 – Created on

05/07/2019 – Updated to add Model Year and correction section.

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