check engine light came on after a 20 min idle up here in NH during cold.I have the thick film AMM.Cleaned terminals air filter (K+N) sprayed air mass meter with cleaner.....still 1-2-1.unplugged and it ran ok.disconnected battery check eng light still came back...1-2-1..is my AMM toast? These are hard to find AMM's

FYI: I have had a LH 3.1 AMM fail when cleaned with AMM spray cleaner.


Also FYI, I have the LH 3.1 specific parts for sale; AMM, ECU and TPS. Since the LH 3.1 AMM is hard to find, I always carried a spare.

Was there any work done on the car recently.

One thing that happens to 740s is that one of the pins in the plug gets pushed back, causing a poor connection. This condition will be apparent when you pull the boot back.

thanks for the comments....the terminals and wires on the AMM connnector look really good.Art, the wires read just like you mentioned...I'm not quite up on voltage testing but the first 2 you mentioned were near 0 and the orange one read just about 12 volts....I put the meter on 12 v....is that correct? Does this mean the Amm is bad? Yes the K and N is oiled I cleaned it was not that dirty at all.Noticed that brass part in the air box was a bit corroded sprayed it with Blaster.

found a cheap air mass sensor online and put it in and check engine light is gone and car runs fine.must have been the sensor

Hi,

You mentioned that the "brass part" in one of your posts was corroded. That is the air filter box thermostat which controls the air filter box flapper which directs either cold or hot air toward your AMM.

If NH has strict guidelines you may need to keep the associated parts in place-air box thermostat, exhaust to air box hose. So you should probably purchase a new air box thermostat (I think it's only around $10) because that is very likely the culprit that fried your AMM (as I think a failed thermostat defaults hot air).

You may want to temporarily disconnect the exhaust to air box hose until you replace your air box thermostat as it could fry your new AMM in short order.

Travis

Travis,

I also notice OP is using an oiled foam K&N air filter. We've heard from many who abandoned the airbox for one of these found it was the cause for their failed AMM later. I'm guessing the preheated air and thermostat aren't any longer in the picture. Cone filter is not an upgrade on a 240.
--
Art Benstein near Baltimore

A dog teaches a boy fidelity, perseverance, and to turn around three times before lying down.
-Robert Benchley

Assuming you've checked the connector for corrosion... Peel the boot back on the AMM's connector. Turn the key on to KP-II but don't start the motor. Measure the voltages on the four terminals. Put your voltmeter's negative lead on the battery negative terminal.

The one with the brown/black wire should read near ground, very close to the one with the green/yellow wire.

The orange wire should have battery voltage.

The red/white wire should have a small voltage which will vary upward when you give the accordion hose a squeeze or waft some air toward the front of the AMM. If not, the AMM is not working. Is that K&N something you oil? And aren't these -001 AMMs also used in the 850?
--
Art Benstein near Baltimore

I used to be indecisive. Now, I'm not so sure...