Piston Slap: Xterra's External Air Bag Influencers?

Ok Sajeev, I got one for you.

I own a 2009 Nissan Xterra 4wd X model. It has nearly 100k miles on the clock. In the past week, whenever I start the vehicle, I hear a chattering noise coming from the passenger side dashboard. The noise persists as long as the passenger air bag light is lit; when that light goes off, the chattering stops. So I took the truck to my local Nissan dealer, whom I trust, and I was told that the problem is the passenger side blender door of the HVAC system – apparently there are gears in this assembly which are not moving freely or properly.

The cost to repair is estimated at about $600 because of the necessity to remove the whole dashboard. The dealer’s service people told me to do nothing until the HVAC system fails to function properly, and it is currently functioning properly except for the above described noise. My question: how is a bad blender door mechanism linked to an airbag light? Can airbags chatter on vehicle startup?

Thank you as always for your excellent advice.

Sajeev answers:

First try resetting the air bag light. If that doesn’t work, let’s trust your trusted dealer on the blend door actuator, and allow me to meander as I cannot Google a precise explanation.

I have a similar problem with my (now fully restored) Lincoln Mark VIII after suffering a front-ish fender impact (i.e. airbags didn’t pop). Now the air bag light/buzzer triggers if the headlamps are on during start up. I disabled the automatic headlights and delayed my knob twisting, keeping the Air Bag Diagnostic Monitor happy.

Which makes me happy, and I’ve invested in a set of factory shop manuals. (You should too!) So let’s see how two seemingly unrelated items are linked:

After starting the Mark VIII, fuse #10 juices up several things, including that Air Bag Diagnostic Monitor (second box from the left on the bottom). So when I crank on the headlights “too early” after startup, the circuit (in the multifunction switch?) drops the amount of juice (voltage?) which upsets the Air Bag Diagnostic Monitor’s 22 year-old circuits. My logic is pathetic, but the result is clear.

What’s the point? Air Bag health indicator modules are, as they age, hyper sensitive to external influences.

If anything looks wrong, the system is engineered to assume the worst and get the owner into a repair shop. This ensures fewer manufacturer lawsuits the air bag system will never be neglected and always save lives.

Just buy the shop manuals with wiring diagrams, please!

[Image: Nissan, Sajeev Mehta]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.