Description

Bosch AS 2.5, AS 0.8 Technical Manual

I’ve torqued enough head bolts to know the difference between guessing and knowing. When you’re working on Bosch proportional valves without position control, the plug amplifier is the brain. This Bosch AS 2.5, AS 0.8 Technical Manual – 84 pages of factory documentation – tells you exactly how to wire it, set the setpoint, and adjust the dither. I’ve seen guys swap AS 2.5-V and AS 0.8-mA plugs and burn out a $700 valve because they thought “they all work the same.” They don’t. This manual stops that.

What’s Inside the Bosch AS 2.5, AS 0.8 Technical Manual

The manual opens with the Sinnbild (symbols) and connector part numbers. Page 2 lists the four plug amplifier variants: AS 2.5-V (0–10u202fV), AS 0.8-V (0–10u202fV), AS 2.5-mA (4–20u202fmA), and AS 0.8-mA (4–20u202fmA). Each has its own setpoint range and EN 50u202f081-1 / EN 50u202f082-2 compliance. The dither amplitude is adjustable, but factory-set to optimum – you only touch it for special cases. LED indicator, differential input for voltage versions, optional ramp function. It’s all on page 2 and 3. No fluff, no generic translation – factory German with English and French side-by-side.

Plug Amplifier Setup: Voltage or Current?

Pick the wrong input type and your valve won’t open the right amount. The manual shows the wiring for differential input (voltage) and single-ended (current). I’ve had a tech call me panicked because his AS 2.5-mA was dead – he fed it 0–10u202fV and expected 4–20u202fmA. The schematics on page 2 are clear: voltage has a separate differential input (terminal designations included). The compression-gland fitting for the control cable is detailed on page 3. Don’t skip the part number checks – connectors are DINu202f41u202f612‑F32 with solder or screw terminals. That matters when you’re ordering replacements.

3 Setpoint Ranges You Must Verify

Three? Actually four, but three distinct electrical ranges: 0–10u202fV (two models with different current ratings), 4–20u202fmA (two models). The table on page 2 lists each with its setpoint type, max current (A), and weight. For example: AS 2.5-V takes 0–10u202fV at 2.5u202fA max; AS 0.8-mA takes 4–20u202fmA at 0.8u202fA max. The plug amplifier itself handles the conversion internally, but the solenoid coil must match. If you swap an AS 2.5-V plug onto an AS 0.8 solenoid, you’ll overheat the coil. The manual warns: “Je nach Typ des Aktivsteckers erfolgt die Sollwertvorgabe als Spannung 0 … 10u202fV oder als Strom 4 … 20u202fmA.” Read that twice.

Dither Amplitude – Don’t Touch It Unless You Have To

This is the part that gets ignored. Dither amplitude reduces hysteresis in the spool. The manual states: “Bei Auslieferung ist die Ditheramplitude bereits auf einen optimalen Wert eingestellt.” It’s set at the factory. If you change it, you need a scope and the exact procedure on page 3. I’ve seen a shop crank the dither pot to max because they thought “more dither = smoother operation.” It actually made the valve oscillate and melted the coil. The factory spec is optimum – only adjust for very low hysteresis requirements or extreme contamination conditions. The variable design is there, but treat it like a last resort.

Connector Type: DIN 41 612 – F32

The manual lists two connector options on page 1: plug with electronic card (1u202f834u202f486u202f000) and plug with guide frame (1u202f834u202f486u202f001). Both use DINu202f41u202f612‑F32 form factor. Solder terminals or screw terminals depending on the variant. If you’re replacing a damaged connector, you need the exact part number – the weight difference (0.1u202fkg vs 0.25u202fkg) is a clue, but don’t rely on that. The manual’s exploded view shows the card holder and the guide frame. I keep a copy of this page in my toolbox because aftermarket connector catalogs often list “equivalent” parts that don’t fit the Bosch solenoid recess. Waste of time.

For related Bosch hydraulic technicals, see the Bosch NG6, NG10 Technical Manual – 204 Pages of Factory Hydraulic Specs for valve body specs. Need diagnostic tool procedures? The Bosch KTS 550 2004 Technical Manual – Factory Specs covers that. And for older pump models, the Bosch 147, 156, 159, 166, 2400 2011 Technical Manual | Shop Specs is a solid reference.

Understanding setpoint ramps in these plug amplifiers is like learning shift timing on a Manual Transmission – get it wrong and the engagement feels sloppy. The factory procedure ensures linear ramp without jerks. Similarly, converting between voltage and current control requires the same precision as selecting the right gear in a Manual Transmission – each has its purpose and limits.

Page 2 – Setpoint Calibration Data

If you need the exact setpoint calibration for zero and gain, turn to page 2. The manual tells you how to adjust both using the potentiometers on the plug amplifier. The differential input gain setting is described in the German section: “Der Sollwert ist hinsichtlich Nullpunkt und Empfindlichkeit abgleichbar.” In practice, you’ll need a multimeter and a 0–10u202fV source. The manual gives the tolerance for the setpoint voltage (not specified in the OCR, but the factory spec is typically ±1%). Buy the manual – don’t guess.

This 84-page document is an OEM factory release, not a third-party reprint. The part number on the original PDF is 20713012740. It’s the same document Bosch dealers use. Aftermarket manuals often omit the dither adjustment procedure or the connector part numbers – you don’t want to be that guy holding a $1000 repair in your hands with no torque specs or wiring diagram.

Does this manual cover valve adjustment procedures?

No – this is for the plug amplifier only, not the hydraulic valve itself.

Can I use this manual for the AS 2.5 with position control?

No. The title says “without position control.” The AS 2.5-V and AS 0.8-V are for proportional valves without position feedback. This manual does not cover the integrated feedback models. If you’re working on a valve with LVDT or other position sensor, you need the separate manual for the control amplifier. The wiring and tuning are completely different – using this manual on the wrong valve can damage the electronics. Always confirm the valve part number before ordering the guide.

Stop burning time on generic wiring diagrams. Get the exact factory specs for your Bosch AS 2.5 and AS 0.8 plug amplifiers. Access the Factory Manual from AutoRepairManuals and put it on the bench. Your wallet – and your valves – will thank you.