Testing The MAF Sensor Circuits (1997-1999 Ford 4.6L, 5.4L)

TEST 5: Checking MAF RTN Circuit For Short To Power Or Ground

In this section, we're gonna' perform another set of tests on the MAF RTN TAN/LT BLU wire (you've already checked it for continuity in TEST 3).

Now, we're gonna' make sure that the MAF RTN circuit is not shorted to power or Ground.

Specifically, we need to make sure that the MAF RTN circuit IS NOT shorted to: 1) Chassis Ground (PWR GND) or 2) VPWR (vehicle power).

The TAN/LT BLU wire (MAF RTN circuit) of the MAF sensor connector connects to pin 36 of the 104 pin PCM connector.

IMPORTANT: Do not probe the front of the PCM 104 connector or you'll damage the terminal. This will require that you replace the entire engine wiring harness.

OK, these are the test steps:

1. 1

   Disconnect the battery negative cable and then unplug the PCM from its connector.
   
   IMPORTANT: The battery negative cable will remain disconnected from the battery negative post for the remainder of the test. This will render the power circuits without battery power and make possible the multimeter continuity tests.

2. 2

   Connect the breakout box to the 104 pin PCM connector only. Do not connect the the Ford 104 pin breakout box to the PCM.

3. 3

   Place your multimeter in Ohms mode (Ω) to check for shorts to power by measuring resistance between:
   
   Breakout box pin 36 (MAF RTN) and breakout box pin 71 (VPWR).
   
   Breakout box pin 36 (MAF RTN) and breakout box pin 97 (VPWR).
   
   Continuity SHOULD NOT exist between any of the indicated pins above.

4. 4

   Place your multimeter in Ohms mode (Ω) to check for shorts to Ground by measuring resistance between:
   
   Breakout box pin 36 (MAF RTN) and breakout box pin 24 (PWR GND).
   
   Breakout box pin 36 (MAF RTN) and breakout box pin 103 (PWR GND).
   
   Continuity SHOULD NOT exist between any of the indicated pins above.
   
   NOTE: Pin 24 and Pin 103 are Ground circuits that connect to chassis Ground.

5. 5

   Your multimeter SHOULD NOT register continuity between the pins tested in step 3 and step 4.
   
   To be a bit more specific: Your multimeter SHOULD NOT register a resistance of 5 Ohms or less. The resistance value should be 10,000 Ohms or more (usually OL).

Let's take a look at what your test results mean:

CASE 1: Your multimeter DID NOT register continuity in the pin tests above. This is the correct and expected test result and tells you that the TAN/LT BLU wire of the MAF Sensor connector is not shorted to power or Ground.

So, what does this all mean? Well, if you've reached this point, by following all of the test steps from the beginning of this tutorial, you have confirmed:

• That the MAF sensor itself is OK (TEST 1).
• That the continuity of the MAF SIG circuit is OK. In other words, the LT BLU/RED wire is not open between the MAF sensor connector and the PCM connector (TEST 2).
• That the continuity of the MAF RTN circuit is OK. To be more specific, the TAN/LT BLU wire is not open between the MAF sensor connector and the PCM connector (TEST 3).
• You have also confirmed that the MAF SIG and MAF RTN circuits are not shorted to power or Ground (TEST 4 and TEST 5).

So, you can conclude that the problem causing the MAF senosr code, on your Ford vehicle, is not due to a short or open between the MAF connector and the PCM connector in the LT BLU/RED or the TAN/LT BLU wire.

CASE 2: Your multimeter registered 5 Ohms or less in one of the pin tests above.

This test result tells you that the MAF RTN TAN/LT BLU wire is shorted to the specific circuit (wire) that registered continuity on your multimeter.

Your next step is to physically check the length of the engine wiring harness (between the MAF sensor connector and PCM connector) for any obvious damage.

Repairing the short between these two circuits will solve the MAF sensor problem lighting up the check engine light (CEL) on your Ford vehicle.

More Ford 4.6L, 5.4L Diagnostic Tutorials

You can find a complete list of Ford 4.6L, 5.4L diagnostic tutorials in this index: Ford 4.6L, 5.4L Index Of Articles

Here's a small sample of the articles you'll find there:

• How To Test The Fuel Pump -No Start Test (Ford 4.6L, 5.4L).
• How To Test The Crankshaft Position Sensor (Ford 4.6L, 5.4L).
• How To Test Ford Coil-On-Plug Ignition Coils 4.6L and 5.4L V8 Engines (at: easyautodiagnostics.com).
• How To Test The Throttle Position Sensor Ford, Mercury, Lincoln 4.6L and 5.4L Engines (at: easyautodiagnostics.com).
• How To Test The FORD MAF 4.2L, 4.6L, 5.4L Round Air Filter Canister Assembly MAF Sensor (at: easyautodiagnostics.com).
• How To Test Ford MAF Sensors Using a Multimeter (at: easyautodiagnostics.com).