Your Silverado isn’t running right, and to make things worse the check engine light is brightly lit up on your Chevy instrument cluster. Using an OBDII scan tool, you have been able to identify an existing Silverado P0171 trouble code. Problem is, you aren’t sure how to fix Silverado P0171 problems in your Chevy truck.

Not to worry, because today I’ll be showing you how to clear your Silverado check engine light and fix your P0171 trouble code. The P0171 GM OBDII DTC Trouble Code relates to the Powertrain Control Module (PCM) seeing too much air from the upstream oxygen sensor. To begin fixing Silverado P0171 issues, we will start with the mass air flow sensor.

When your Silverado P0171 trouble code is triggered, your Chevy Malfunction Indicator Lamp (MIL) will turn on. This error can cause driveability issues because the PCM sees the engine running without enough fuel, and cannot compensate correctly. There’s a number of reasons that this can be happening in your Silverado.

Today I’ll be showing you how to test, diagnose and troubleshoot the Silverado P0171 OBDII Trouble Code. Our test truck is a 5.7 liter GEN III GM engine found in a 2005 Chevy. Need a guide on the LM7? I’ve got a guide on how to clear P0171 trouble code in a Chevy Express van here.

Symptoms of P0171 Trouble Code

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• Sluggish acceleration
• Black or thick smoke from tailpipe
• Rough idle
• Motor stalls when load is applied

Other related OBDII DTC Trouble Codes

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1. P0101 – MAF sensor diagnostic trouble code
2. P0102 – Lean and/or Rich diagnostic trouble code
3. P0174 – Lean diagnostic trouble code

Possible Causes of P0171 Trouble Code

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• Air Intake Leak
• Bad or lazy oxygen sensor
• Faulty Mass Air Flow Sensor
• Improper Spark Plug Gap
• Poor Fuel Quality

I’ll be showing you how to Test Your MAF in your 5.7 liter GEN III GM engine, and giving you a step by step guide on what to look for when troubleshooting your MAF for the Silverado P0171 OBDII DTC Trouble Code.

How To Test Your MAF ( GM 5.7 Liter – LM7 Engine )

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Your 5.7 liter GM mass air flow sensor ( MAF ) is connected by way of a five pin weatherproof engine plug that connects the MAF to the Powertrain Control Module (PCM). To begin testing your MAF, you will need a multimeter and to locate the sensor itself, which should be located next to your air box.

The mass airflow sensor reads the incoming air charge, along with other values such as air intake temperature, barometer, and others to accurately feed the PCM the data that it needs. Your GM PCM will use this value along with other vital engine sensor outputs to orchestrate your engine spark and fuel delivery.

Once you have located your mass air flow sensor, pull the white locking tab up and out of the connector. Once you have pulled out the white tab, you should hear a slight click as the internal locking clip comes free.

With this white locking tab pulled out and free, you can now unplug your MAF and inspect the connector.

Before we begin testing your mass air flow sensor, let’s take some time to look at the wires and what they are for your connector.

Testing the Mass Air Flow Sensor for Power

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There are two wires that you’ll need to check for power to see if your MAF is indeed turning on with the key set to the “ON” position. If your ignition is not turned to the “ON” position, do this now, but make sure your engine is not running. There are two wires that are needed to power your Mass Air Flow Sensor on this GM 5.7 liter engine.

As you can see, Pin 4 and Pin 3 are the two power and ground wires that you will need to test first. Set your multimeter to DC mode and put the black (negative) test lead on the negative terminal of your battery. Now with the red test lead, put it to the front of the wiring harness in question, probing Pin 4, or the switched power wire for a power signal. If you do not have a power signal here, check your ignition switch to make sure it’s set to the “ON” position.

Now reverse your test leads and put the power to the positive terminal of your battery and test the middle wire, or the low reference wire on Pin 3 for a ground signal.

If these two wires check out, you will need to move on to the kHz testing section of our Test Your MAF article.

There are three signal wires on your mass air flow sensor harness, but Pin 5 is the one we’re most interested in.

Testing your MAF Sensor for Signal

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Here is the part where I’ll be showing you how to test your MAF sensor for the proper Hz frequency output range for the amount of air your engine happens to be ingesting. Plug your MAF back into place and backprobe Pin 5 or the first pin on the left hand side with the connector plugged in. Here we go with the 5.7L LM7 MAF wiring pinout again.

• 5.7L GM MAF Pin 1 – Air Temperature Sensor Circuit
• 5.7L GM MAF Pin 2 – Air Temperature Sensor Circuit
• 5.7L GM MAF Pin 3 – Circuit labeled 3:Ground Circuit.
• 5.7L GM MAF Pin 4 – Circuit labeled 4:Power (12 Volts) Circuit.
• 5.7L GM MAF Pin 5 – Circuit labeled 5:MAF Signal Circuit.

The MAF sensor is responsible for converting the incoming air charge to a value in Hz that the PCM can translate and use. You will be measuring this output value with the engine on and running. Before conducting this test, make sure the engine bay is clear of any tools or debris and that you come nowhere near the fan assembly, as it can turn on without warning.

Turn the multimeter on and turn to read the Hertz frequency, now backprobe Pin 5 with the engine starting and running. Read and record the data being output by the MAF sensor, this Hz reading is what your PCM sees in real time.

Either have a friend gently depress on the accelerator, raising the engine’s RPM which should in turn raise the Hz output from the MAF sensor. As your RPM’s begin to climb, the incoming air charge should raise the Hz reading from the MAF. You should see a smooth curve in frequency that should match how far the throttle plate and engine speed rises. There should be no jumps or spikes in frequency, test this wire and signal using a variety of RPM speeds and throttle position sensor openings.

If the Hertz (Hz) signal DID NOT rise smoothly nor decreased smoothly on your multimeter, you will need to replace your MAF to resolve your P0171 trouble code.

The part number for the replacement MAF sensor, and NOT the housing is 10349461. Please let me know if you have any questions or comments regarding the P0171 GM 5.7 liter Test Your MAF Guide.