Correct functioning of the hot wire air flow sensor can be checked by measuring the following signal voltages, see figure 1: Channel Probe Voltage Range 1 Sensor output signal 8 V Ground on battery 2 Positive side of sensor power supply 20 V Negative side of sensor power supply.
Figure 1: Measuring diagram. Figure 2: Measuring a working mass air flow MAF sensor. Download hot wire sensor measurement Figure 3: Lab scope measurement of hot wire air flow sensor Channel 1 red shows the signal of the hot wire air flow sensor and channel 2 yellow the power supply of the sensor. The following signal deviations can indicate a problem: No signal: Cause: back probes have no connection perform a connection test , no power supply, sensor defective Signal voltage to high: Cause: poor or no ground on power supply, sensor defective Signal shows more noise than example signal: Cause: wiring of signal wire or power supply damaged, poor connection in connector terminals, sensor defective Signal shows an offset in relation of the example signal: Cause: scope is not set to DC coupling: , poor power supply to air flow meter, false air leaking into the air intake system, sensor defective.
Measure lead TP-CB. Disclaimer This document is subject to changes without notification. All rights reserved. Safety warning:. Before measuring, check that sources of dangerously high voltages are switched off or shielded from contact.
Keep a clean working environment when doing measurements. TiePie engineering can not anticipate the safety actions that need to be taken to protect persons and appliances.
Due to the high hertz a voltmeter is not a suitable device to measure this, as it will display the average value of the frequency. Instead an oscilloscope is needed that can measure frequent enough to display graphs that will allow you to see the exact frequency at any given time. With time dirt and contaminants in the air is burnt on the hot wire deteriorating its accuracy. The most common symptom of this contamination is a hesitation or a time- lag in engine response that is felt after the accelerator pedal is depressed.
Some of the surface contaminants can be removed using electronic s spray cleaner or a similar solvent spray or by keeping it submersed within a solvent for a period of time.
Some MAF sensors incorporate a self-clean feature very similar to self-cleaning ovens where the wire temperature is increased to very high temperature in order to burn off any contaminants.
This feature is typically enabled when the engine is turned off. In-depth knowledge breakdown of the various components of a car. Since a number of other parts i. Installed in the intake pipe between the air filter housing and the intake manifold, most MAF sensors work on the hot wire principle. Put simply, a MAF has two sensing wires.
One is heated by an electrical current, the other is not. As air flows across the heated wire, it cools down. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate.
The current is then changed to a frequency or a voltage that is sent to the ECU and interpreted as air flow. The quantity of air entering the engine is adjusted accordingly. Since the MAF sensor is responsible for measuring air flow into the engine, they have a lot of air passing through them. Figure 2: Measuring on a working hot wire sensor with frequency output.
The following signal deviations can indicate a problem: No signal: Cause: back probes have no connection perform a connection test , poor or no power supply to sensor, sensor defective. Measure lead TP-CB. Disclaimer This document is subject to changes without notification. All rights reserved. Safety warning:. Before measuring, check that sources of dangerously high voltages are switched off or shielded from contact.
Keep a clean working environment when doing measurements. TiePie engineering can not anticipate the safety actions that need to be taken to protect persons and appliances. Before starting a measurement, check which safety measures need to be applied.
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