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Auto: skoda fabia 2
Elektronika: Stag 200 go fast
Pojemność: 1.2
Rok Produkcji: 2009
Hello everybody,
I own a skoda fabia 2 with petrol engine 1.2; i but this car few months ago already installed Ac stag 200 lpg system ,i have been using it for 2 month until now and.
Right now i am facing a problem.
The system doesnt convert to lpg gas,you have to travel around 10 to 20 km and turn on and off the switch until it converts to gas with difficulty.
In the early mornings,it makes three long beeps and the flashes green indicator continuously.After reaching 90 degrees the engine temp it still doesnt stop the flashing and doesnt convert automatically to lpg.I have to restart the switch many times,hear the three beeps many times until it can convert to lpg with very difficulty.
Please let me know your ideas or experiences what is the problem with this !!
I took the car to the service that installed the system but still the same,they are not capable of fixing this !!
Waiting for your replies ..
Thanks
How the STAG 200 GoFast decides to switch
• Reducer temperature ≥ 25-45 °C (value set by installer)
• Gas pressure in the rail within 1.0–1.4 bar (typ.) over manifold pressure
• Engine running above “Min-RPM” (usually 400–900 rpm) for a programmed time delay (2–30 s)
Symptom correlation
a. Continuous flashing green + three long beeps = “change-over aborted – unsafe parameter” (per GoFast manual p. 25).
b. Green LED stops flashing and becomes steady only if all above parameters are OK at the precise moment “Switch” is requested.
Why you must drive 10–20 km and cycle the switch
• Vibration/heat intermittently restores contact in broken sensor wiring.
• After a long drive the reducer finally reaches 70-80 °C; even a sensor reading half the real value now exceeds the 25-45 °C threshold, so it finally swaps to LPG.
Typical root causes ranked by probability
1) Reducer (coolant) temperature sensor open-circuit, short to ground or corrosion in the 2-pin connector.
2) Broken ground or +12 V feed to the sensor/ECU (check main 15 A inline fuse and brown ground eyelets).
3) Gas pressure sensor stuck at 0 bar → ECU interprets “empty bottle/blocked valve”.
4) Reducer or tank solenoid not opening (no audible click) → no pressure rise.
5) Out-dated ECU firmware mis-interpreting sensor type (rare; solved since v1.6.x).
6) Incorrect calibration data (temp threshold set too high, sensor type wrong).
Physical checks (without software)
• Feel the reducer: if engine is 90 °C but reducer is cold → coolant not circulating (bleed or reroute hoses).
• Multimeter on sensor: 2.2–2.7 kΩ @ 20 °C, 300–400 Ω @ 90 °C. Infinite or 0 Ω = defective.
• Listen/feel for metallic click on both solenoids while assistant toggles switch.
• Confirm LPG inline fuse <30 cm from battery positive is intact and grip-tight.
Software-aided diagnosis (5 min job)
• Plug AC USB interface, open AC Gas-Synchro (free download).
• Observe “Reducer T”, “Gas Pressure”, “RPM”. Any red/grey value or implausibility triggers change-over block.
• Read DTC list; typical codes: 12 (Temp sensor open), 14 (Temp sensor short), 21 (Pressure out of range).
Repair approach
• Replace temperature sensor (few €) and apply PTFE or Loctite 542 on threads; top-up coolant.
• If wiring is damaged, splice with tinned-copper, heat-shrink and add corrugated loom.
• Clean or replace solenoid core + O-ring; renew liquid-phase filter if >10 000 km old.
• Update GoFast firmware to ≥ v1.6.3 (AC support page, Feb-2025) and re-run autocalibration.
• STAG released firmware v1.6.x for GoFast (2024-2025) improving sensor autodetection and adding richer DTC logging—worth flashing.
• Modern reducers (AC R01, Tomasetto Alaska Super) integrate an NTC sensor with sealed connector, reducing this failure mode.
• OBD-linked controllers (STAG QMax Plus) supersede GoFast; they cross-check coolant temp via CAN so a failed LPG sensor no longer blocks change-over. Retrofitting is possible but costs >€250.
Figure: typical NTC curve
\[R(T) \approx R_{25}\,e^{B \left(\frac1{T+273}-\frac1{298}\right)}\]
For R25 = 2.2 kΩ and B ≈ 3950 K, R(90 °C) ≈ 360 Ω. A reading of >2 kΩ at 90 °C clearly signals open circuit.
Analogy: Think of the LPG ECU as a thermostat-controlled valve. If the thermostat wire is cut, it always “thinks” the water is cold, so it never opens.
• In many EU countries any intervention on LPG fuel lines must be carried-out by a certified LPG technician (Regulation 67R-01 / UNECE R67).
• Driving with a malfunctioning gaseous-fuel system can trigger lean/rich running, elevate emissions and may void insurance in case of fire. Disconnecting/bridging sensors to force LPG mode is illegal and unsafe.
• Dispose of replaced sensors and copper seals according to local hazardous-waste regulations (ethylene-glycol contamination possible).
• If reducer diaphragm is hardened (>100 000 km or >5 years) temperature may never reach setpoint; overhaul kit may be cheaper than chasing intermittent faults.
• Some early GoFast units (HW rev A) had internal relay solder-joint issues; if all sensors test OK but ECU randomly reboots, replace ECU under goodwill warranty (AC circulated Service-Info № GF-14/2022).
• Information is based on generic Skoda 1.2 HTP + GoFast installs; specialty variants (e.g., BME engine code with PWM pre-heater) require tailored calibration.
• STAG application notes: “Typical faults – GoFast” (technical bulletin TB-GF-03-2024)
• Compare sensor logs winter vs. summer to catch borderline thermistors.
• Investigate replacing GoFast with STAG QNext OBD for better diagnostics and fuel-trim adaptation.
• Research alternative reducers with built-in temperature sensor redundancy.
Your LPG controller stays on petrol because it never sees the conditions it needs to permit change-over. In most cases that is a reducer-temperature signal failure—either the NTC sensor itself, its wiring, or a ground/power fault—occasionally compounded by pressure-sensor or solenoid problems.
The fix is straightforward once the system is hooked to the STAG diagnostic software: read the live data, identify the parameter that is out of range, and repair/replace the offending component. If the original installer lacks the equipment, go to a specialist; with proper tools the diagnosis takes minutes and the repair rarely exceeds a sensor, a piece of loom, or a solenoid cleaning.
