Checking the air mass sensor: causes, diagnosis and troubleshooting

Air-mass sensor

10037926a_AM0_white_inclined

The air-mass sensor calculates the intake air mass in internal combustion engines. The engine control requires this variable in order to control a wide range of functions. This page explains the design and function of the air-mass sensor. You will also find information about how a faulty air-mass sensor can manifest itself, the causes leading to its failure, and how it can be checked in the workshop.

The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

Air-mass sensor function

The air-mass sensor is used to measure the intake air mass. It consists of a tubular housing with flow straightener, sensor protection, and sensor module. It is mounted in the intake pipe between the air filter housing and the intake manifold.

Two temperature-dependent metal film resistors affixed to a glass membrane are arranged in the air flow. The first resistor (RT) is a temperature sensor and measures the air temperature. The second resistor (RS) is used to detect the air flow rate. The resistor RS cools down to a greater or lesser degree depending on the intake air flow. In order to balance out the constant temperature difference between resistors RT and RS, the current flow through resistor RS must be dynamically regulated by the electronics. This heat flow is used as a measured variable for the respective air mass that is taken in by the engine. This measured value is required by the engine management control unit to calculate the fuel quantity required.

Testing the mass air flow sensor

Testing the mass air flow sensor: Example OK — Air-mass sensor – Example OK

The following test steps should be considered during troubleshooting:

1

Checking the plug connection

Check plug connection for tight fit and correct contact.

2

Checking the air-mass sensor

Check the air-mass sensor for damage.

3

Checking the measuring elements

Check the measuring elements for damage.

4

Checking the voltage supply

Check the voltage supply

5

Checking the connecting cables

Check the connecting cables between the removed control unit plug and the sensor plug for continuity (circuit diagram required for pin assignment). Reference value: approx. 0 ohms.

6

Electronic test of the air-mass sensor

Electronic test of the air-mass sensor through the engine management control unit. When a fault occurs, a fault code is stored in the control unit that can be read out using a diagnostic unit.

Not helpful at all

5

4

3

2

1

Very helpful

Spare Parts Finder

OE-No. Manual Vehicle Identification Universal Parts

Spare Parts Finder

Simple vehicle identification Also determine spare parts with OE numbers Detailed product information Find wholesalers near you

You might also be interested in

Basic Knowledge

E-mobility in everyday workshop activities: technology and requirements

Electromobility is changing workshop processes: find out how workshops handle high-voltage systems, new diagnostics procedures and targeted qualifications

Reading Time: 16 minutes

Basic Knowledge

Starter damage assessment

Starter faulty? Spot typical causes such as overloading or misfiring and find out how to repair damage effectively.

Reading Time: 1 minute

Basic Knowledge

Alternator damage assessment

How to diagnose damage to the alternator: ranging from corrosion and short circuits right up to bearing damage.

Reading Time: 1 minute

Basic Knowledge

Intake-air temperature sensor - checking & faults

Discover how to check the intake air temperature sensor for defects and how to replace it efficiently.

Reading Time: 3 minutes

Basic Knowledge

TPS sensor – function & troubleshooting

Learn how to check a throttle potentiometer for defects and recognize the most common symptoms.

Reading Time: 2 minutes

Basic Knowledge

Coolant temperature sensor testing

Instructions for testing the coolant temperature sensor with a multimeter - diagnosis and repair for your workshop.

Reading Time: 3 minutes

Basic Knowledge

Lambda sensor testing and troubleshooting

Find out how to check and measure lambda sensors - with step-by-step instructions for fault diagnosis.

Reading Time: 14 minutes

Basic Knowledge

Idle speed controller & actuator - function & check

Everything you need to know about testing and troubleshooting idle speed regulators: function, typical symptoms and repair tips for your workshop.

Reading Time: 3 minutes

Basic Knowledge

Camshaft position sensor - function & troubleshooting

Learn all about the function and testing of the camshaft sensor and possible symptoms of a defect.

Reading Time: 2 minutes

Basic Knowledge

Car knock sensor - function & troubleshooting

Find out how to check the knock sensor for malfunctions and rectify possible fault symptoms.

Reading Time: 2 minutes