Tuesday, February 1, 2011

Mass Airflow Sensor find and fix in 1997 Nissan Pathfinder

Posted the core of this to FixYa and thought I'd add more detail and post it here as well, in case someone searching can benefit from this random part failure:

One day, out of the blue, my Pathfinder engine cut out as I started to drive.  It then cut out randomly.  The way it was failing 'felt' electrical in nature, like a connection was going bad.

So, I'd start the car and quickly run out and start tapping on all things electrical.  The MAF, or Mass-Airflow Sensor (not to be confused with MAP, the manifold air pressure), is located on the front airbox-airtube assembly and was a natural to tap on.  I got lucky.  The first think I tapped on killed the engine.
Did it again... and again, and again.  The Mass Airflow Sensor was definitely to blame.

I realized that it was caused by vibration, and that I could "reset" the car while driving as long as I didn't get above about 2700 RPM's.  I was in "safe mode".  Riiiight.

Got home, looked at the prices of these buggers, and they were in the $300-$800 range.  Eep!

For that price, I'm going in!
(I also verified the MAF sensor code with my newly built USB to OBDII converter found here.  It was the P0100 "MAFS" error)
I removed the MAF sensor by unscrewing the 4 screws and gently lifting it out of the air passage.

With the screws off, I was able to gently pry the cover off.  What I found was a little controller board encased in a jelly, presumably to isolate the board from the elements, and three little thin wires leading to the external connector.  Without even having to break out the multimeter, I could tell that one of the wires had broken due to vibration fatigue or some other manufacturing defect.  I recall I had to break all three wires to get the thing to open fully.

Soldering this was very difficult due to the presumably silicone jelly.  It made the metal very resistant to bonding with solder.   Without digging too much into the jelly, I exposed all wires and eventually, with scraping, fire, and flux, managed to get solder to stick decently to the various wires, adding my own jumper wires to make it easier to bridge the gap and close the case.

I needed to make this fix road-worthy, so I folded their wires around an insulating piece of clear plastic I cut from some plastic packaging material.  The wires folded nicely around it into place and the case closed.

Several years later, the fix is holding strong, or so it's continued functioning would lead me to believe!

I hope someone out there found this useful, please comment if you do.

1 comment:

Huang Lissa said...


The acid should be diluted with an excess of water to give a 5 to 10-folddilution. The liquid should then be neutralized by mixing with an equal volumeof agricultural lime, or other alkaline material containing lead-acid batterycalcium carbonate, orsodium hydroxide. Use ofhydrated lime has the advantage of lower cost per unit of neutralizing capacitywhen compared to sodium hydroxide.