K&N MAF Sensor Test Results - January 2004 through December 2017

K&N has millions of satisfied customers, yet we do occasionally get instances where a dealership or service provider has blamed our product for a vehicle problem. We attempt to resolve these misunderstandings by speaking directly to the service technicians. In issues regarding MAF sensors, we have been able to recover many of the allegedly "bad" sensors and test them to diagnose the actual cause of the failure. In most of these cases the "bad" sensor was actually functioning properly and was misdiagnosed by the dealership or service provider. The diagram below is a summary of our findings.

Of the 139 sensors we received that were truly malfunctioning, 46 had a complete electronic failure in which the sensor's voltage output was a flat line, generally caused by a connection or circuitry problem within the sensor. When a sensor is responsive but it's voltage output is not within the normal limits we refer to this as "out of range". This condition can be caused by circuitry problems and it can also be caused by a sensor's thermistor becoming dirty or contaminated. We sent 34 out of range sensors to an independent laboratory for an elemental and chemical analysis and the majority of them were found to have silicone as the contaminant.

Silicone is used on the circuitry of these sensors because it acts as an excellent thermal and electrical insulator, inherently sticks to most surfaces, and is resistant to moisture and heat. Some MAF sensors use a high temperature burn-off cycle to eliminate normal engine contaminants from the sensor. Silicone is resistant to this process.

Thermistors are used in MAF sensors to measure the transfer of heat from the thermistor to the air passing by the sensor. A thermistor's resistance changes as its surrounding temperature changes. The greater the air mass and air flow the greater the transfer of heat. When a thermistor is "silicone contaminated" the thermistor becomes insulated and can result in an out of range condition.

In addition to out of range sensors, functioning and failed sensors have also been sent to an independent forensic laboratory for analysis. A few of these sensors were found to have trace amounts of oil on the thermistor. The amount of oil was so minimal that an accurate analysis of the oil's source could not be determined. The trace amount of oil can conceivably be found from two possible sources: fuel in the combustion chamber or motor oil used as an engine lubricant that gets suspended in crankcase vapor. Our experience in the lab is that trace amounts of oil don't change the sensitivity of the sensor enough to cause an "out of range" electronic signal. Furthermore our testing has shown that K&N air filter oil will not come off a K&N air filter even in extreme conditions. More on this topic here.

As of the date of our last test shown below, K&N air filter oil cannot be confirmed as the source of contamination on a sensor nor can any oil type be attributed to a sensor’s failure.

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More Details On Silicone & Testing

Mass Air Flow Sensor Electronic Testing at K&N:

The MAF sensor is placed on a test bench designed and built by K&N Engineering. The test bench can flow air through the sensor at variable flow rates, ranging from idle to full throttle. The flow of a sensor is then compared to a new sensor.

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Microscopic Examination:

When a service technician looks at a MAF sensor's thermistor what they see with their naked eye is very little. It is nearly impossible to determine if a MAF sensor's thermistor is dirty or clean from looking at it without magnification and good lighting. When K&N views a MAF sensor, we look at it under a microscope. Below are sample images under microscopic view.

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A MAF sensor is located under the hood of your vehicle and is subject to a heat, cold, vibration, etc., in other words, a hostile environment. An engine performing as expected can contribute to contaminating a MAF sensor. The presence of gas fumes, a vehicle backfiring, combustion blow-by and even water condensation can contribute to contamination of a sensor. Ironically, the presence of contamination does not necessarily conclude the sensor is not functioning properly and requires replacement.

Independent Forensic Analysis:

An elemental and chemical analysis of the contamination has more often than not shown to be silicone. K&N filter oil does not contain silicone. The silicone can actually be traced to the sensor’s housing of the electronic circuitry. The silicone can seep out of the housing area onto the sensor.

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MAF sensor thermistor probes connect to the circuit board. Silicone covers the circuit electronics and it can seep down contaminating the thermistor. This photo shows the silicone compound referenced, covering/protecting the electronics. The probes leading to the thermistor are connected to the underside of this circuit board.

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This photo shows a probe demonstrating the stickiness of the silicone material.

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This photo shows a sensor with silicone covering the electronics. Note the small gold processor in center.

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This photo is a close up of the processor under the silicone.

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This photo is an extreme magnification of the processor. As can be seen, this is a complex sensor with thousands of connections and components all of which must be intact for the sensor to function properly.

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Below is a more detailed summary of our actual test results.

	Quantity	Initial Sensor Test	Electronic Test Result	Microscopic Examination	Independent Laboratory Chemical Analysis	Probable Cause
Electrical Conduction Failure within Sensors	20	Bad	Failure	Clean	N/A	Electrical Failure
	11	Bad	Failure	Dirty	N/A	Electrical Failure
	6	Bad	Failure	Dirty	Silicone	Electrical Failure
	1	Bad	Failure	Dirty	Trace Oil	Electrical Failure
	1	Bad	Failure	Dirty	Silicone & Trace Oil	Electrical Failure
	8	Bad	Failure	De-lamination	N/A	Manufacturing Defect
	33	Bad	Out of Range	Clean	N/A	Electrical Failure
	26	Bad	Out of Range	Dirty	N/A	Electrical Failure
	31	Bad	Out of Range	Dirty	Silicone	Electrical Failure
	1	Bad	Out of Range	Dirty	Silicone & Trace Oil	Electrical Failure
	1	Bad	N/A	Dirty	Silicone	Severe Silicone Leak
	139 BAD

 

	Quantity	Initial Sensor Test	Electronic Test Result	Microscopic Examination	Independent Laboratory Chemical Analysis	Probable Cause
Normally Functioning Sensors *	190	Good	Normal	Clean	N/A	Sensor Never Failed
	70	Good	Normal	Dirty	N/A	Sensor Never Failed
	2	Good	Normal	Dirty	Dirt	Sensor Never Failed
	30	Good	Normal	Dirty	Silicone	Sensor Never Failed
	3	Good	Normal	Dirty	Trace Oil	Sensor Never Failed
	3	Good	Normal	Dirty	Trace Oil & Silicone	Sensor Never Failed
	298 GOOD

 

Electrical Failure: Electrical issue within sensor compared to a new sensor's specifications
Manufacturing Defect: A layer of the membrane sensor peels back causing electrical failure - known as de-lamination
Sensor Never Failed: Service provider error; sensor was not malfunctioning
Severe Silicone Leak: The silicone leak was too severe to run on the test stand

* Well over 50% of the "damaged" sensors sent to us were functioning properly meaning they were never damaged in the first place and cannot be attributed to any vehicle problem. Click here for more information on how this may happen.

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Below is the list of MAF sensors that were sent to K&N for testing. The list includes dealerships that misdiagnosed the problem and blamed a K&N product for the failure. Test results are also shown.