The boost pressure limit on a VW MED17 lives in the Protection / error tables section, not in the boost-control area you’d expect. It looks like a diesel-style limit: atmospheric pressure on one end, an unrealistically high cap on the other. Select the working area, write a round value in mbar absolute (1500 mbar = 0.5 bar boost), and the PID controller will hold to it. The wastegate setup auto-scales because it’s coded for the low-compression range too.
This is the text summary. Members at our May 2026 Q&A live saw me find this map on screen in WinOLS — opening the file, walking past monitoring / driver wish / wastegate sections, and landing on the Protection table. For the full Bosch EDC17 / MED17 map context, see our Bosch EDC17 tuning guide →. Register free for our next Open Q&A → — live with me, agenda forming.
The question — from Q&A live 2026-05-05
Denis asked:
“Can you explain, using the example of the same VW Caddy 1.4TSI, which maps regulate the turbocharger’s inflation? For example, we want to limit the inflation pressure to 0.5 bar.”
The 0.5 bar target turns this from theory into a setpoint — a concrete number to hit.
Why direct pressure limits are rare in modern Bosch
“The limitation of the pressure is not very popular in the modern issues — they are rather focusing on the flow. But we can always go and try to find the limitation of the pressure, which is usually not written as the flow.” (~47:08)
Modern Bosch ECUs (MED17 and newer EDC17 versions) shifted the boost-control logic from pressure-based to flow-based. The pressure limit didn’t disappear — it just moved out of the obvious place and stayed as a backup envelope.
Where to find it on MED17
Walking through the file in WinOLS, the boost-related zones appear in this order:
- Monitoring section — driver’s wish + port monitoring
- Speed of turbocharger
- Wastegate / valve control
- Efficiency of turbocharger
- Error tables / Protection section ← the pressure limit lives here
“There is an error tables / Protection — so here we have the example. That was just a limit of the pressure. You can notice that this is just like a diesel limit — here we have the atmospheric pressure, this one is very very high. I don’t know what for it is so high, but the map is working in this area.” (~48:10–48:30)
The map shape is recognisable once you know to look in Protection: atmospheric pressure as the low boundary, an unusually high value as the upper boundary, and the actual working area between them.
How to set 0.5 bar
“You can just simply write here, or just select everything and write the round limit values. Then the maximum permitted pressure by you — it will be for example 1500. And then you will have the limitation. So when it will be hit, the system will reduce the PID control to keep that pressure.” (~48:35–48:55)
The mechanic:
- Select the working zone of the map (or the whole map if simpler)
- Write a round value in mbar absolute — for 0.5 bar boost above atmospheric: 1500 mbar
- Save and flash — when the limit is hit, the PID control will reduce to hold the system to that pressure
Why mbar absolute, not gauge: Bosch encodes pressure as absolute, so atmospheric ~1000 mbar + 500 mbar boost = 1500 mbar absolute = 0.5 bar gauge boost. Writing 500 directly would limit the engine to half-vacuum, not 0.5 bar boost.
What if you only see flow maps?
If the file you’re looking at has no clear pressure-limit map and only flow values, you can still cap boost — just convert flow to pressure conceptually:
“We can also do the same by the flow … but we need to calculate the pressure from the flow — so capacity of the engine, divided by the flow, divided by the capacity of the engine, will just tell us about the actual value of the boost. More or less, of course, because it is not an exact conversion. But this is also possible if you do not find the perfect map.” (~49:10–49:50)
The math gives an approximate boost value from a flow value. Use it to identify which flow-limit value corresponds to your 0.5 bar target, then cap the flow map at that value.
For the live WinOLS walkthrough of the flow→pressure conversion (with factor + offset setup in Properties → Conversion), see KB-14 → — the EDC17 C46→C64/C74 substitution case where Bosch removed the pressure map entirely and only flow remains.
Bonus: the wastegate setup auto-scales
“Another good information is that the wastegate setup is done also for very small compressions. So in that case, if you just change it to be 1.5, this one — we have also pre-scaled proper setup. So the car will work with that lower pressure, because it is already coded in the system.” (~49:50–50:15)
The PID + wastegate calibration covers a wide compression range out of the factory — including the low end. When you cap pressure to 1500 mbar (0.5 bar), the existing wastegate map already handles that range. No need to re-tune the wastegate response curve to match the new ceiling.
What this means for tuning
To limit boost on MED17, two things matter:
- Where to look — Protection / error tables, not the boost-control section
- What to write — round mbar-absolute value, the PID + wastegate calibration scales to it automatically
The same protection-section pattern applies on most MED17 variants and on older EDC17 versions where pressure maps still exist. On newer EDC17 (C64, C74), the pressure map was substituted with flow — the conversion approach above lets you set the same effective limit.
Related on Tuners Guild
- EDC17 boost-map traps + the live flow→pressure conversion demo: KB-14 Why do EDC17 boost maps look broken — and why did Bosch switch to mg/cycle in C64/C74?
- Bosch EDC17 / MED17 generic context: Bosch EDC17 tuning guide →
- Gasoline torque-conversion path on MED17: KB-11 MED17 torque conversion path — pairs with this KB for the full MED17 boost-control picture
- Full gasoline workflow: Chip Tuning Gasoline — Practice course (22 chapters, includes MED17, SIMOS, DENSO pipelines)
Want the full MED17 boost-control workflow?
Limiting boost is one piece of the boost-control chain — driver’s wish, torque request, wastegate PID, efficiency map, monitoring shadows. Our Chip Tuning Gasoline Practice course covers all of them in sequence: where each map lives in WinOLS, how the maps interact, and the protection layers that catch tunes the engine can’t actually run.
See the Chip Tuning Gasoline course →
Your turn
Set a boost limit on a MED17 variant other than VW Caddy 1.4TSI — or on a different gasoline ECU family (SIMOS, DENSO, Bosch ME7)? Post your case:
- ECU + car
- Section where you found the pressure-limit map (Protection / boost-control / something else)
- Round mbar value you wrote
- Whether the PID + wastegate held the new ceiling without further tuning, or needed adjustment
Cross-platform comparisons sharpen the mental map of where boost protection lives across modern gasoline ECUs.