From Ross-Tech Wiki
17664/P1256 - Engine Coolant Temperature Circuit (G62): Open / Short to B+
- Difficulties with starting a cold engine.
- Diesel: an indication is extreme long time burning time of the glow indication light.
- Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 - 3000 rpm.
- RPM at idle is irregular.
- With all engine temperatures seldom idle rpm will vary between 900 - 1000 rpm.
- With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C.
- Bad acceleration during warming up.
- Wiring and/or connections faulty
- Engine Coolant Temperature Sensor (G62) faulty
- Check wiring and connections
- Check / Replace Engine Coolant Temperature Sensor (G62)
- In MY 1995-2002 (?) in Europe at VW-cars the G2/G62 had the bad reputation of breaking down often. The default G2/G62 is black and all replacements are green.