Air Flow Meter – Hot Wire

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Operation Steps:

1. Open the software, select “Vehicle->Diagnosis->Setup”, as illustrated in Figure 7.1.2.

2. Click “Ignition->Primary-> Primary Ignition (Voltage)”, and click “OK”, as illustrated in Figure 7.1.3.

3. Click “OK”.

Figure 7.1.2

Figure 7.1.3

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Primary Ignition

Connect the Oscilloscope

1. Plug the 20:1 Attenuator (HT201) into channel 1 on the oscilloscope and plug a BNC test lead

(HT30A) into the attenuator.

2. Place a large black gator clip(HT18A) on the black test plug (negative) and a small red gator

clip on the colored test plug (positive).

3. Place the black gator clip onto the battery negative terminal and probe the coil's negative terminal

with the small red crocodile clip.

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Note

The sensor will have varying electrical connections and may have up to four wires; it reacts to the oxygen

content in the exhaust system and will produce a small voltage depending on the Air/Fuel mixture seen at

the time. The voltage range seen will, in most cases, vary between 0.2 and 0.8 volts: 0.2 volts indicates a

lean mixture and a voltage of 0.8v shows a richer mixture.

A vehicle equipped with a lambda sensor is said to have 'closed loop', this means that after the fuel has been

burnt during the combustion process, the sensor will analyze the emissions and re-adjust the engine's fuelling

accordingly.

Lambda sensors can have a heater element to assist the sensor reaching its optimum operating temperature.

Zirconia sensors when working correctly will switch approximately once per second (1 Hz) and will only start

to switch when at normal operating temperature. This switching can be seen on the oscilloscope, and the

waveform should look similar to the one in the example waveform. If the frequency of the switching is slower

than anticipated, remove the sensor and clean with a solvent spray and this may improve the response time.

The sensor is inoperative below 300℃.

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Reference Waveform

Example waveform

Figure 6.6.5

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Operation Steps:

1. Open the software, select “Vehicle->Diagnosis Setup”, as illustrated in Figure 6.6.2.

Figure 6.6.2

2. Click “Sensors-> Lambda Sensors -> Lambda Sensor Zirconia”, and click “OK”, as illustrated in Figure 6.6.3.

Figure 6.6.3

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Connect the oscilloscope

1. Plug a BNC test lead (HT30A) into channel 1 on the DSO3064(A).

2. Fit a large black gator clip on the black (negative) plug on the test lead and an acupuncture probe

(HT307) or multimeter probe on the colored (positive) plug.

3. Place the black gator clip to the battery negative terminal and probe the lambda sensors output

connection with the acupuncture or multimeter probe as illustrated in Figure 6.6.1.

Regardless of the number of wires connecting the lambda sensor to the vehicle's ECU, the output

from the sensor will invariably be on the black wire.

Figure 6.6.1

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Electrical Connections (zirconia type only)

Single wire: this wire is the self-generated voltage output from the sensor and is generally black in color.

Two wires: this will have an output wire and an output earth return.

Three wires: this will have a single output wire and two wires for the heater element (supply and earth).

The internal heating element raises the temperature to ensure faster control when starting from cold.

Four wires: this unit has a signal and signals earth return wires. The additional two wires are for the heater

element.

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The titania oxygen sensor differs from the zirconia sensor in the fact that it is incapable of producing its

own output voltage and is therefore reliant upon a 5 volt supply from the vehicle's ECU. The reference

voltage is altered according to the engine's air-fuel ratio, with a lean mixture returning a voltage as low

as 0.4 volts to a rich mixture producing a voltage in the region of 4.0 volts.

A constant high voltage output from the zirconia shows that the engine is running constantly rich and is

outside the ECU's adjusting range, whereas a low voltage indicates a lean or weak mixture.

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The lambda sensor is essentially two porous platinum electrodes. The outer electrode surface is exposed

to the exhaust gasses and is coated in a porous ceramic with the inner coated surface exposed to fresh air.

The most commonly used sensor uses a Zirconia element, producing a voltage when a difference in oxygen

content is seen between the two electrodes. This signal is then sent to the Electronic Control Module (ECM)

and the mixture is adjusted accordingly. Titania is also used in the manufacture of another type of lambda

sensor that offers a faster switching time than the more common Zirconia sensor.

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Lambda Sensor - Zirconia

The lambda sensor is also referred to as the Oxygen O2 sensor or a Heated Exhaust Gas Oxygen

(HEGO) sensor and plays a very important role in the control of exhaust emissions on a catalytic

equipped vehicle. The lambda sensor is fitted into the exhaust pipe before the catalytic converter;

cars using the new EOBD2 will also have a post cat lambda sensor.

The sensor will have varying electrical connections and may have up to four wires; it reacts to the oxygen

content in the exhaust system and will produce a small voltage depending on the Air/Fuel mixture seen at

the time. The voltage range seen will, in most cases, vary between 0.2 and 0.8 volts: 0.2 volts indicates a

lean mixture and a voltage of 0.8v shows a richer mixture. A vehicle equipped with a lambda sensor is said

to have 'closed-loop', this means that after the fuel has been burnt during the combustion process, the sensor

will analyze the resultant emissions and readjust the engine's fuelling accordingly. Lambda sensors can have

a heater element which heats the sensor to its optimum operating temperature of 600℃, this enables the sensor

to be located further away from the heat source at the manifold to a 'cleaner' location.