Variable Camshaft control in BMW-s is usually referred to as VANOS. This page has some notes about
- low-side NFET type (injection, ignition IGBT or extra NFET) to switch negative side to GND
- or hi-side PFET outputs (extra PFET-output) to switch positive side to +12V.
- Most Vanos solenoids are around 11 .. 12 Ohm, so current might exceed 1A, and stepper outputs are not recommended and not supported (unless with an external driver stage, that is actually simple to implement)
- p259 outputs can work with external driver (FETs with flyback diodes), usually with 1k .. 2k7 Rgs for PFET
- or 510 .. 1k Ohm pullup for NFET: will be inverted that way and NFET activated for some time after powerup (p259 output activation from software will turn off the NFET).
See
- MembersPage/GunnarReynisson/VariableVanos
- MembersPage/SFiftyBthirtyTwoVanos
- InputTrigger/BmwDoubleVanos
Normally variable timing (VVTI or Vanos) solenoids are powered by constant +12V on one pin and controlled by low-side outputs as sane engineering practice applied generally. (For example BMW M50 Vanos is sane).
In VEMS ECUs there are plenty N-FET type low-side driver outputs anyway, eg. free injector output or IGBT ignoutput, the ECU switches GND as usual), so the extra NFET-outputs are optional (useful if 8 cylinders consume many outputs, or other special relays or actuators are planned to be connected).
Some Vanos solenoids require Hi-side PFET outputs
- Hi-side PFET outputs: 2 or 4
If the Vanos solenoid is driven by high-side output
- if the ECU switched +12V (perhaps the BMW engineers lost their medicines those days),
- and accordingly: the direction of flyback diode molded in the VANOS solenoid connector is connected with common anode to GND
- which is not easily changed; measure this diode to verify the drive polarity
- such as most S54B32 (iirc S50 also), then Hi-side P-FET outputs are recommended.
So please check the Vanos solenoids and measure diode polarity (and determine power direction)
- and never forget to mention the exact engine model.
BMW usually requires 2 outputs per Vanos solenoid. See [camshaft angle control in VemsTune help]