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It's the demand sensor. Get it warrantied.
PO155 = inconsistant signal from track C-D, the white marked side of demand sensor. Any reading outside of the 600-1400Mv range = bad sensor
Reading this got my curiosity. So I googled the "Demand Sensor" and found that it's a problem component throughout several Aprilia and Guzzi models. I just wonder why it's such a bad part and whether the manufacturer has improved the reliability or if the replacements are still the same?
hmmmm - tank removal necessary?
The demand sensor is a sort of four way TPS. It has four tracks that all have to produce signals that correspond with each other. If they don't it triggers a 'Service' or 'Urgent Service' warning as it means the ECU might incorrectly open the throttle if it were to rely on a single, wrong, reading. It's a four way redundancy to make sure that can't happen.Pete