Hello , 

Any idea where is odometer sensor is  located in a 37meter Sany concrete pump based on a Isuzu chassis

the sensor for rpm is located om the cab side of the pto box. It needs a 4mm gap or less between the sensor and the signaling plate tabs. Sometimes the plate halves break off. Another suggestion is there's a plug up about 16 inches up from the sensor and sometimes unplugging it and plugging I back in can make a better connection. Contact putz parts for replacement sensors and signaling plates if your are bad. They should have them in stock