Sensor fault judgment and solution - Autonics

1. Air flow meter problem

Problem characteristics: The vehicle is shaking at idle, high fuel consumption, weak at high speed, and black smoke from the exhaust pipe.

View and analysis: through the fault diagnostic instrument detection, the engine air flow meter data block is severely exceeded, the reason for the damage of the air flow meter is often the use of inferior air filter or the air filter is not regularly replaced, resulting in dust staying on the air flow meter hot wire for too long, resulting in its resistance value change, prohibition or failure, and dust will cause the throttle body to be too dirty.

Knowledge of car repair

The identification and treatment of air flow meter problems are as follows

(1) Identify the cause

Detect engine air flow meter data flow, out of range. High fuel consumption, weak acceleration, and black smoke from the exhaust pipe. According to the data flow combined with the fault phenomenon, the air flow meter fault is identified.

When accelerating, the injection pulse width is added, but the air flow rate does not fluctuate at all, so the air-fuel ratio will be inappropriate, and it will inevitably accelerate the weakness.

(2) Processing

Replace the air flow meter, clean the throttle body, and replace the original air filter.

Sensor fault judgment and solution - Autonics

Sensor fault judgment and solution - Autonics

Sedan knowledge

What is the effect of an air flow meter?

The effect of the air flow meter is to detect the air intake of the engine, and convert the air intake information into an electrical signal and input it into the electronic control unit (ECU) for accounting and confirming the fuel injection volume.

The air flow meter used in Volkswagen is an L-shaped hot film air flow meter, which is installed between the air filter housing and the intake hose. The core component is the flow sensing element and the thermal resistance (both platinum film resistors) are combined to form a thermal film resistor. A rectangular sheath is provided on the air intake channel inside the sensor, which acts as a sampling tube, and the thermal film resistance is set in the sheath.

2. Oxygen sensor problem

Problem characteristics: unstable idle speed, excessive fuel consumption. Damage to the oxygen sensor causes the engine to underpower, slow acceleration, and black smoke from the exhaust.

View and profile: View and dissect the engine with a problem diagnostic, extract fault codes, and investigate data streams. The air-fuel ratio and the working condition of the oxygen sensor are determined by the voltage fluctuation and frequency of the oxygen sensor. If it works properly, the voltage should be changed between 0.4 – 0.6V; If the change range is between 0.1 and 0.9V, it is clear that the change of concentration and dilute of the mixture may be the fault of the injector leakage or blockage, and if it does not change at 0.45V, then it can be judged to be the fault of the oxygen sensor.

Knowledge of car repair

The identification and treatment methods of oxygen sensor problems are as follows:

(1) Identify the cause of excessive engine fuel consumption and severe black smoke. Check the engine with a fault diagnostic instrument, investigate the data flow, the frequency of change of the oxygen sensor voltage is 10-20 times/s, which is the more ambitious working condition, if it is lower than 10 times/s, then the oxygen sensor can be preliminarily identified, if the voltage of 0.45V has not changed, then it can be judged that the oxygen sensor is damaged and the signal is interrupted.

(2) The treatment method replaces the oxygen sensor, re-detects it with a fault diagnostic instrument, tests it normally, and the fault is removed.

Sedan knowledge

What is the mission of the Oxygen Sensor?

The oxygen sensor is mounted on a three-way catalytic converter. According to the voltage signal of the oxygen sensor, the engine ECU dilutes or concentrates the mixture according to the theoretical optimal air-fuel ratio of 14.7:1 as close as possible, so the oxygen sensor is the key sensor for electronically controlled fuel metering.

The oxygen sensor is the primary component that provides the mixture concentration information, which is used to correct the fuel injection volume, realize the closed-loop control of the air-fuel ratio, and ensure that the air-fuel ratio of the engine is close to the theoretical air-fuel ratio.

Sensor fault judgment and solution - Autonics

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