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The electronic dipstick

On engines that have one, the oil level sensor sits in the oil sump and measures how high the oil stands. The engine control module (ECM) reads the sensor and keeps the result as a value in millimetres, alongside the oil temperature and the engine speed. That is the "electronic dipstick" people talk about: not a separate gadget, but a few numbers inside the engine module.

A raw height on its own is not very useful, though. To know whether 30 mm is plenty or too little you need two more things: the engine's own MIN and MAX limits, and the conditions under which the reading is valid. Both are defined by the manufacturer for each engine, and both are part of the oil level check routine that a workshop tool runs.

How the engine's own oil level check works

The clearest way to explain it is with a real example. Our test car is a 2008 C70 with the 2.4-litre five-cylinder diesel, engine code D5244T8 (an EDC16 engine module). The same oil level check is defined for that engine family — D5244T8, D5244T9 and D5244T13 — in the C30, S40, V50 and C70 of roughly 2006–2010. It reads three values from the engine module:

The check then repeats a simple loop, every three seconds:

1. Read the oil temperature. At 60 °C or below it reports "oil temperature too low" and waits. At 100 °C or above it reports "oil temperature too high" and waits.
2. Read the engine speed. At 300 rpm or below it asks you to start the engine and waits.
3. Only then read the oil level, correct it to 90 °C and place it on the MIN–MAX scale.

The scale for this engine runs from 19 mm (MIN) to 42 mm (MAX) of corrected level — a window of 23 mm. The result is shown as a percentage: 0 % is the MIN mark, 100 % the MAX mark.

Why the oil has to be warm

The routine is strict about temperature for a reason: the sensor's reading depends on it. The check corrects every reading to a reference temperature of 90 °C, adding 0.18 mm for each degree the oil is below 90 °C (and subtracting it above). That correction is only trusted inside the 60–100 °C window; outside it the check refuses to give a number at all.

A worked example shows how much it matters. Say the sensor reports 30 mm with the oil at 70 °C:

• Correction: (90 − 70) × 0.18 = 3.6 mm, so the corrected level is 33.6 mm.
• On the scale: (33.6 − 19) / 23 ≈ 63 % between MIN and MAX.

Without the correction the same reading would come out at about 48 %, a difference of roughly a sixth of the whole MIN–MAX window from temperature alone. And a reading taken with the oil at 30 °C would not be valid at all, because the engine's own check would not measure.

The engine running matters too. The check will not measure with the engine off, so a "quick look" with only the ignition on does not count. For the most accurate result:

• drive or idle until the oil is properly warm — ideally close to 90 °C;
• park on level ground;
• let the engine idle for about three minutes;
• keep the car stationary in P or neutral with the parking brake on, somewhere well ventilated.

Other engines, other limits

The 19–42 mm window and the 60–100 °C range belong to this particular diesel. Other engines have their own oil level checks with their own MIN and MAX, their own temperature range and correction — or no oil level sensor at all. There is no single "Volvo oil level" figure that applies to every car, and copying numbers from a forum thread about a different engine will give you a wrong answer.

That is also why a tool cannot simply hard-code one scale. The right limits have to come from the definition of the engine that is actually in the car, which in turn depends on the model, year and engine — see our guide to Volvo's P1, P2 and P3 platforms for how much that varies.

What an OBD scanner shows

A generic OBD-II scanner reads the legislated emissions data: the standard list of engine values and the emissions fault codes. The oil level is not part of what it asks for. It is a manufacturer value, stored in the engine module and returned only to Volvo's own diagnostic requests.

On the D5 engine above, those requests are Volvo's D2 messages: each value is fetched from the engine module by its own record identifier, then converted with that engine's scaling formula — the raw oil temperature, for example, is stored in tenths of a kelvin and has to be converted to °C. A generic scanner neither sends those requests nor knows the formulas. The same thing is behind most "my scanner shows nothing" stories; we cover it in why a generic OBD-II scanner misses Volvo fault codes.

Even a scanner that can show the raw value in millimetres leaves you with half the job: you still need the temperature, the correction and the MIN and MAX limits for your engine. A manufacturer-level read does all of that together, the same way the engine's own check does.

How Volscan shows the oil level

Volscan shows the oil level as a MIN–MAX gauge: a band between the two marks with a marker for the current level. The limits, the temperature correction and the measuring conditions are not typed into the app by hand; they are taken from the oil level check defined for the engine in your car. On our C70 that gives the 19–42 mm window and the 60–100 °C range described above.

• When the oil is too cold or too hot, or the engine is off, Volscan tells you what is missing instead of showing a misleading number.
• As soon as the conditions are met, the level appears, already corrected to 90 °C.
• If your engine has no such check in its definition, there is no scale to draw, so Volscan shows the plain sensor value instead of inventing limits.

Reading the result is simple. Below 0 % the level is under MIN: top up. Above 100 % the engine is overfilled and the excess should be drained. If the level climbs between oil changes without any topping up, have the car checked — fuel in the oil is one possible cause.

Like every Volscan function, the oil level is read-only: it asks the engine module for values and changes nothing. We are still comparing the sensor reading with the physical dipstick on our test car and will update this article with the result. See the supported cars and adapters.