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Discussion Starter · #1 ·
Hey Y'all,

GF has a 2003 Xterra 4x4 without the supercharger. So it's got the 3.3L VG33E. Bought the car used about 3 months ago with 170K miles and timing belt recently done.

I'm an off-road guy, and my car knowledge is mostly suspension-related. Apologies in advance if these are dumb questions.

Background
3 weeks ago we're idling in traffic, and it's about 90 F outside. Check engine light comes on. We pull over and I check the code with my OBD2 reader: P0174 (System too lean - bank 2). No biggie. I thoroughly clean the MAF with MAF cleaner. Really soaked that SOB. Let it dry for about an hour. Pop it back in, take it for an hour test drive on a mix of back roads and high way: no codes. car is driving great.

This lasts up until last Wednesday. GF tells me the car stalled on her while idling at a light. Started right back up, bucked a little bit on the highway (her words), and stalled again as she pulled into the driveway. Service engine soon light is on. I check the code: P0103 (high voltage on the MAF sensor).

Didn't want to jump the gun and buy a new MAF. So I hit Google and searched this forum. I read through a lot of threads with P0103, but...
  1. It was almost always paired with another code (we've only got the 1)
  2. The person asking for help wouldn't check voltages or do meaningful diagnostics
I found the links to the FSM as well as this troubleshooting article. The FSM DTC guide is like 3 steps for P0103, and I have a decent multimeter. Seems easy, but I'm really struggling (pretty sure the problem is me). So I come to you all asking for clarity around the DTC procedure before I take it to the local Nissan dealer.

Troubleshooting
  • Logged the MAF rate with OBDFusion
    • Let the car get up to temp for about 5 minutes prior to starting this log file. RPM was around 600-700, which I think is pretty standard for this engine.
    • All data points are with the car idling. It didn't stall for me during this process (was hoping it would).
  • 77220
    • FSM says air flow rate should range between 0.9 - 5.8 gm/s, but this has some spikes where the gas wasn't pressed.
    • Does this chart look problematic?
  • Followed the DTC procedure for P0103.
    • Step 1: check terminal 2 in MAF plug with Multimeter: 12 V (woo!)
    • Step 2: this is where my idiot self gets lost
      • Turn ignition switch OFF. (easy)
      • Disconnect ECM harness connector. (done).
      • Check harness continuity between mass air flow sensor terminal 3 and ECM terminal 55. Refer to Wiring Diagram.
        • help: is this just a matter of getting a long enough piece of wire and alligator clips, then doing a continuity check with 1 end in the ground of the MAF harness plug and the other in ECM terminal 55?
      • Also check harness for short to ground or short to power.
        • help: is there something special I should be checking? I assume it's obvious, and I'm an idiot because the FSM didn't go into extra detail like it did for the other tests?
If I can get these questions answered, then I think I'm good to go. The rest of the steps are the same (except terminal 54), and checking voltage while car is started (I can use the paperclip trick to piggyback on terminal 54 with the harness plugged in for that.

Really hoping the wiring checks out. If so, I'll grab a hitachi MAF from O'Reilly and give that a try before taking it to the dealer.

Thank you in advance! I'm new to the world of nissans, but spend a ton of time over in iH8mud for my GX470.
 

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Discussion Starter · #4 ·
Yes. I just want to make sure I perform the test correctly as it involves the ECM, and I don’t want to screw it up.
 

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2002 Xterra SE, Shock Blue, AT/4x4
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gxor_dude Great write up and diag! I am chasing an errant MAF issue myself on my 2002, and I have tested these circuits a few times. Answering your questions:
-First, make sure you check the ground connections on the intake manifold! They are usually up on top and easy to see, very close to the wire harness across the top of the upper manifold. Sometimes get forgotten on repairs.
-The graph is really helpful, and I would say the spikes are problematic and likely causing your code (high voltage). As you probably know by now, the MAF interpolates a current measurement into a voltage measurement (within the MAF) and the ECM reads this voltage. Logically, if the engine is idling with all accessories and a/c off, the engine wouldn't likely suck that much air in a short period of time. It would be more gradual up to and following the maximum. This tells me the MAF is wiggin out internally.
-Continuity test: you are right, get a longer wire with clips to allow for the distance between the meter and ECM connector. Just make sure to zero your leads to take into account the additional wires when you're ready to take a measurement. Continuity should be near 0 ohms (very low resistance). A higher resistance (maybe 5? 20? ohms) could be considered "continuity", but would indicate higher resistance in the circuit that might be problematic. However, this would show up as lower voltage on your graph and may be imperceptible. I think the spikes are your issue.
-Short to ground/power: with the MAF and ECM disconnected, the wires between the two should be completely disconnected from everything including power and ground. If you test at the ECM and MAF pin to ground and power, you should see "OL" on your meter showing open circuit-which it should be. If you see any resistance, you may have wiring harness damage which is really unlikely unless caused by somebody or something like a mouse. Or, in the case of my battle, perhaps water is bridging a circuit in a connector somewhere.
-Terminal 54: be very careful when measuring this with a paper clip or t-pin not to touch other wires or any grounding point. Insulate or tape the lead/pin if it could be an issue.
Good luck with your repair!
 

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Discussion Starter · #7 ·
Thank you!!

thought those spikes seemed a little fishy given the idle engine. your explanation makes a ton of sense, and was my take as well. If the MAF says there’s a lot more air coming through, then the hot signal wire would see a jump in voltage to keep the temp.

appreciate your guidance on the electrical tests. I think I’m all clear on what to do for the continuity test between the ecm and the MAF harness.

I’m a little unclear on the test for short to ground / power.

If you test at the ECM and MAF pin to ground and power, you should see "OL" on your meter showing open circuit-which it should be.

am I thinking about this right? Ignition off, MAF harness not plugged into the MAF sensor, ECM harness not plugged into the ECM. One of the probes plugged into the MAF harness ground pin and one probe to battery power? I think I read not to put the probe from the multimeter on the positive plug in the maf harness while having the probe on the ground pin in the harness at the same time.

sorry if this is a dumb question. Just never tested electrical components before.
 

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2002 Xterra SE, Shock Blue, AT/4x4
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Thank you!!

thought those spikes seemed a little fishy given the idle engine. your explanation makes a ton of sense, and was my take as well. If the MAF says there’s a lot more air coming through, then the hot signal wire would see a jump in voltage to keep the temp.

appreciate your guidance on the electrical tests. I think I’m all clear on what to do for the continuity test between the ecm and the MAF harness.

I’m a little unclear on the test for short to ground / power.

If you test at the ECM and MAF pin to ground and power, you should see "OL" on your meter showing open circuit-which it should be.

am I thinking about this right? Ignition off, MAF harness not plugged into the MAF sensor, ECM harness not plugged into the ECM. One of the probes plugged into the MAF harness ground pin and one probe to battery power? I think I read not to put the probe from the multimeter on the positive plug in the maf harness while having the probe on the ground pin in the harness at the same time.

sorry if this is a dumb question. Just never tested electrical components before.
No problem! I hope you get it solved.
As far as the short to ground/short to power, what you are looking for is a short circuit in the wiring. Below is a quick sketch I put together. The red lead is the positive multi-meter lead on the disconnected MAF connector pin (the ECM is also disconnected), the black is the negative lead to engine/chassis ground. You shouldn't see anything on the meter, it's open circuit-two parallel lines never touching. Same for checking short to power (black dotted line is the black lead for step 2). In the case there is a short to ground (purple line), you will have continuity between the MAF pin and ground because of the short circuit (literally a shorter path to ground). The meter sends a signal through the red lead, travels through the MAF pin and wire, through the purple short circuit (could be a screw, bare wires touching, smashed connector, water in connector, etc.) to ground where your meter receives the signal showing a completed circuit. The actual meter could read 0.1 Ohms or maybe more depending on what the short circuit is. Again, I highly doubt this is the case, but for a matter of understanding I hope this helps.
77223
 

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2004 Xterra XE 4WD Auto 3.3L NA V6
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I write code all day long. It makes computers do things that people didn't think they could. Even though the pictures are good, I still benefit from a list of instructions.
  1. Start by unplugging both ends as pictured by @BabeTheBlueOx - the MAF and the ECM.
  2. Turn meter to Ohms Ω, preferably one of the lower range settings.
  3. Connect the red lead to the wire pictured - MAF pin #3.
  4. Connect the black wire to the following locations for each of the 3 tests:
    1. Ground.
    2. Battery Positive terminal or a known battery power source.
    3. MAF pin #4 or ECM pin #54.
On all tests, you should see nothing in the readout display. If you do, change the range setting to determine the true degree of the short, but regardless, you will need to fix any short that is identified.

PS: The reason I added test #3 is in case there has been a short between the 2 wires inside the harness from MAF to ECM.
 

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Discussion Starter · #10 ·
Babe, MeToo, thank you both immensely!

the step by step instructions and diagram make the instructions from the FSM quite clear. Gonna try and knock out these tests tomorrow. My gut feeling is that it’s the MAF and not a short based on the prior code about running too lean (and that cleaning the MAF fixed things temporarily).

either way, this is a great learning process. Thanks for the help. I’ll report back with my findings and maybe more graphs.
 

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i got maf codes alot did this and then literally saw the issue staring me in the face, rip in the boot of the intake allowing more air in unmetered and cauing the ecm to think the maf was giving bad readings under conditions than it was, just my 2 cents
 
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