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P0171, P0174 GM vehicles

P0171, P0174 GM vehicles

Diagnose and fix P0171, P0174 GM vehicles

Service bulletin #PIP5549 for P0171, P0174 GM vehicles

GM has issued service bulletin #PIP5549 to address trouble codes P0171, P0174 on GM vehicles listed below.

Vehicles affected

Buick Enclave 2012-2018  3.6 LLT, 3.6LFY engines

Cadillac XTS 2015-2018 3.6 LFXl

Chevrolet Colorado 2015-2016 3.6 LFX

Chevrolet Equinox 2015-2017 3..6 LFX

Chevrolet Impala 2015-2018 3.6 LFX

Chevrolet Traverse 2012-2018   3.6 LFX, 3.6 LFY

GMC Acadia 2012-2017   3.6 LLT

GMC Canyon 2015-2016   3.6 LFX

GMC Terrain 2015-2017   3.6 LFX

Cause of P0171, P0174 and check engine light

GM has determined that a vacuum leak in the foul air tube, intake manifold or purge valve may be causing the P0171, P0174 condition.

Diagnose P0171, P0174

1. With engine at operating temperature, use a scan tool to check and record Long Term & Short Term

fuel trims.

2. Shut off the engine. Then disconnect the foul air tube from the intake manifold as shown. Plug both sides

P0171, P0174

3. Start the engine and check Short Term & Long Term fuel trims.

If both LT and ST fuel trims were positive values above 5% and the value has changed to negative value, replace the foul air tube.

If the previous ST fuel trim value was above 5% and the LT fuel trim was -2% to 2% and the ST has now changed to 0 or a negative value, replace the foul air tube.

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


If the ST and LT fuel trims did not change, perform the purge valve test shown below.

Purge Valve Test

1. Remove the plugs and re-install the foul air tube to the manifold.

P0171, P0174

2. Disconnect vacuum hose and power supply from purge valve

3. Restart the vehicle then place your finger over the open port on the purge valve.

P0171, P0174
4. If you feel vacuum on the valve port, it is leaking and must be replaced

P0171, P0174

Shut vehicle off and then reinstall detached components

If no vacuum was felt at valve port refer to the applicable diagnostic procedure in your shop manual.

Posted on by Rick Muscoplat

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