How to check the 1.8T MAF sensor in VCDS: group 002

Updated: 2026-11-05

Does your 1.8T accelerate poorly, lose power at higher rpm or consume more fuel than usual? The mass air flow sensor (MAF, G70) is one possible cause, but a low reading does not necessarily mean the sensor is faulty. On many older 1.8T engines, VCDS displays intake air mass in group 002, in grams per second.

This guide explains how to distinguish a possible MAF fault from an intake leak or airflow restriction. It covers selected 1.8T 20V engines where group 002 includes an air-mass reading. Verify your ECU's field labels. For instructions on creating a CSV, see How to record a VCDS log.

At a glance: what a healthy log looks like

• At idle: MAF reports a relatively low and stable airflow.
• During acceleration: air mass generally rises with engine speed and load, although its shape depends on the turbocharger and ECU calibration.
• At full load: the most useful information is the peak airflow achieved during the run and whether it is consistent with engine output and behaviour.
• Low airflow does not automatically mean a bad MAF. Possible causes include underboost, a leak, blocked air filter, fuel-supply problem or exhaust restriction.
• Read MAF and fuel trims together, particularly when mixture-related faults are present.

Group 002 in VCDS

For one particular Audi A3 8L 1.8T configuration, workshop documentation describes these group 002 fields:

g/s means grams of air per second. Do not confuse it with mg/stroke, a common unit in TDI logs. Older ECU versions may use different labels. Follow the field name and unit in your own log, not the group number alone.

How to check MAF at idle

1. Warm up the engine. Audi requires coolant temperature of at least 80°C for some tests.
2. Switch off the air conditioning and electrical consumers. The radiator fan must not run during the test.
3. Open 01-Engine → Meas. Blocks - 08 → 002.
4. Record the airflow in field 4 together with engine speed and load.
5. If the reading is outside specification, also check intake leaks and the sensor's power supply and wiring.

For a specific Audi A3 8L four-cylinder turbo system, the documentation gives 2.0–4.5 g/s at warm idle. This is not a fixed limit for all 1.8T versions: ECU calibration, equipment, temperature and auxiliary loads can change the reading.

Source: Audi A3 Mk1 — checking air mass meter G70.

How to log MAF under load

1. After the idle check, select group 002 and click Log → Start.
2. Perform an acceleration test under load in safe, legal conditions. A passenger operates the laptop.
3. To compare airflow with boost, you may also select 115, but additional groups reduce the sampling rate. If sampling is too slow, log 115 separately.
4. Save the CSV and check whether airflow rises smoothly with load and where its maximum occurs.
5. Compare the result with your engine code, stock power, modifications and test conditions.

Do not continue a test if the engine has a serious fault, severe hesitation or overheating.

How many g/s should a 1.8T produce?

Ross-Tech gives a very rough rule of thumb: in a full-throttle pull to the redline in one gear (Ross-Tech suggests second), peak airflow in g/s can be around 0.8 × engine horsepower (hp) under conditions close to sea level. For a stock 150 hp 1.8T, that gives an approximate reference value of 120 g/s.

This is not a factory pass/fail specification for the MAF sensor. Airflow depends on load, boost, altitude, temperature and how power is achieved on a tuned engine. Do not replace the MAF simply because it shows 112 rather than 120 g/s.

Also check whether the engine was actually receiving the requested boost. If the turbo fails to produce enough pressure, low airflow may be a consequence of another fault.

Typical problem patterns

For the documented Audi variant, below 2.0 g/s at idle can be related to unmetered air or a sensor-supply issue. Above 4.5 g/s can come from extra load on the engine from ancillaries, or again from the MAF supply voltage or wiring. This shows why one reading is rarely enough for diagnosis.

Worked example

A hypothetical example, not a real log:

MAF rises, but at 2500 rpm the engine has not yet reached the requested boost pressure. The first row does not prove a MAF failure. Consider the complete curve, achieved load and fault codes.

Fault codes

For P0101, Ross-Tech lists the MAF sensor itself as well as leaks downstream of it, intake/exhaust restrictions and connector or wiring issues.

Common mistakes

• Confusing g/s with mg/stroke. These are different units.
• Treating 0.8 × hp as a strict diagnostic threshold.
• Judging the sensor from idle readings alone.
• Replacing the MAF without checking boost and leaks.
• Evaluating data after lifting off the accelerator. Airflow naturally drops sharply.

Frequently asked questions

Does every 150 hp 1.8T have to show 120 g/s?

No. This is a rough Ross-Tech reference that depends on test conditions. A sound diagnosis requires checking other parameters.

Does low MAF always indicate a failed sensor?

No. If the engine is not receiving enough air because of underboost or an intake restriction, MAF can also read low.

Is unplugging the MAF a definitive test?

No. The ECU may use substitute values and change its control strategy. Feeling that the car “drives better unplugged” does not prove the sensor is faulty.

Where can I analyse my CSV?

Upload the original file to vaglogs and compare airflow with engine speed and boost. The diagnostics flag a MAF that gives no signal (below 1 g/s with the engine running) or whose reading stays frozen on one value while the engine revs through the range, which is the ECU's substitute value. Whether the airflow is plausible for your engine, you judge from the chart. See 1.8T boost — groups 115 and 118 and Fuel trims — group 032.

Sources

• Audi A3 8L: checking air mass meter G70 — group 002.
• Audi A3 8L: evaluating group 002 — possible causes of deviations.
• Ross-Tech Wiki: Fuel Trim Info — MAF and the rough g/s-to-horsepower ratio.
• Ross-Tech Wiki: 16485/P0101 — implausible MAF signal.