How To Test LM7 MAF

September 16, 2014

Expanding on our How to Build a Budget LS Engine series, we’ll be taking a look at how to test, service and repair components for many popular budget GEN III engines. One of the engines we speak about at length in our Budget Build series, is the LM7.

The LM7 is an increasingly popular engine for swappers to choose, because it’s so readily available and cheap. Most LM7 swaps can be found for under 1000 dollars, making it a good candidate for your own LS build. The LM7 engine replaces the older LR4, and checks in at 5.3 liters of GEN III goodness.

Don't forget our LS Sensor Checklist! — Don’t forget our LS Sensor Checklist!

With a longer stroke and slightly larger displacement than it’s predecessor the LM7 is one of the most common engines you can buy. Output from this engine is 275 hp and 320 ft lbs of torque in the most common or pre-2003 trims, after the 2003 model year you have a little bit more power at 285hp and 320 ft lbs, but lose the cable actuated throttle.

The LM7 can be found in many different GM vehicles, but most commonly can be found in these following trucks

2002–2006 Chevrolet Avalanche
2003–2007 Chevrolet Express/GMC Savana
1999–2007 Chevrolet Silverado 1500
1999–2007 GMC Sierra 1500
2000–2006 Chevrolet Suburban/GMC Yukon XL
2000–2006 Chevrolet Tahoe/GMC Yukon

We’re going to be testing the mass air flow sensor in a LM7 engine set today, in the event that you’ve swapped the entire engine into your car already. OBDII DTC Trouble codes that may relate to this issue are : P0101 or P0102 related to the mass air flow (MAF) sensor.

The Mass Air Flow Sensor ( MAF ) for our 2003 LM7 is part number 12574383 or 15926193 from GM and is connected by way of a five pin engine connector. These part numbers are for the Mass Air Flow Sensor and Housing, but can often be labeled as Mass Air Flow Housing.

You can also replace just the sensor itself and re-use your old housing, that GM part number is 10349461. You will need a multimeter or similar voltage reading device to complete our How To Test LM7 MAF Guide.

To begin locate your mass air flow meter, which should be placed inline of your intake snorkel. Put the key in the ignition and turn it to the “ON” position, but do not turn on the motor.

To unplug the MAF connector, you will need to pull up on the white plastic retaining clip that’s part of the MAF connector.

With this white retaining tab pulled up, you can now depress the MAF clip and unplug your mass air flow sensor.

Now inspect the five pin terminal for any damage, and get your multimeter out. You need to put your multimeter in DC mode, and put the black lead on the negative battery terminal.

Take the red lead now and test PIN 2 shown in the diagram above as switched power. You can test the power with the connector off, or backprobe it with the connector back on the MAF.

If you have power at this wire, move on to the middle wire and test here for low reference signal or a ground.

If you have power and ground at these two wires, the next move it to re-connect the MAF plug and backprobe PIN 1 or the MAF signal wire for the kHZ signal being transmitted back to the ECU.

Test the operating range of the MAF signal wire as the last part of our How To Test LM7 MAF article. If these wires do not check out, you either have a failed MAF or a break in the wiring back to your ECU.

Have any questions about our How To Test LM7 MAF Guide? Leave us a comment below!