# 93 hardbody



## Xcab (Sep 3, 2018)

I have a ka24e engine. It has a 2500 rpm rev limiter code from ECU says mac sensor. I have put 3 on it same problem. I have checked continuity in all 3 wires nothing is helping. Anyone have any other reasons for the rev limiter? Thanks


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## jp2code (Jun 2, 2011)

Code 12 Mass Air Flow Sensor Circuit: Is that the code you have?

When the engine's air/fuel calculation does not match up with the amount of air that the MAF says is coming in, it throws Code 12.

Usually, that's because the MAF has gone out or one of the wires to the MAF has a short.

It could also be because you have an air leak between the MAF and the engine or because the sensors that calculate the air/fuel readings are off.

A clogged air filter would also prevent air from flowing through the MAF and getting in from somewhere else.



https://www.autocodes.com/p0101_nissan.html said:


> The Mass Air Flow (MAF) sensor is placed in the stream of intake air. It measures the intake flow rate by measuring a part of the entire intake flow. It consists of a hot film that is supplied with electric current from the Engine Control Module (ECM).
> 
> The temperature of the hot film is controlled by the ECM a certain amount. The heat generated by the hot film is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to maintain the temperature of the hot film as air flow increases. The ECM detects the air flow by means of this current change.


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## Xcab (Sep 3, 2018)

That is the code I am getting. The engine is fresh timing has been checked and double checked. I have put a known working maf sensor as well as a reman and brand new on the truck. Keeps throwing same code.


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## Xcab (Sep 3, 2018)

Also has a new air filter new gaskets on the throttle body and intake.


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## rogoman (Dec 16, 2004)

I'll go along with JP2's recommendations. There may be a major intake system vacuum leak. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. A good place to connect to is the charcoal canister. There should be three hoses connecting the carbon canister. Two of the hoses go to a purge valve that's built into the canister. The second larger hose off the purge valve should be your vacuum line. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps. Here's a picture of the MAF voltage tests:


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## Xcab (Sep 3, 2018)

Thank you both. I will try that and let you know.


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## Xcab (Sep 3, 2018)

Loud humming noise coming from under hood when driving. Any thoughts?


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## Xcab (Sep 3, 2018)

It was a failed intake gasket.


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## Xcab (Sep 3, 2018)

2 wheel drive


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## Xcab (Sep 3, 2018)

Under the hood.


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