Yes I know this is a common problem and there are several other posts on the subject, BUT I am pretty sure that my problem is a dodgy sensor and am looking for some additional info to confirm this before starting the process to import a new sensor from the UK (which is a real schlepp)
Background: the vehicle (1998 4.6 HSE) has been standing for some time (2-3 weeks), has been started occasionally but not driven. Suddenly, just after Christmas, the gearbox overheat message appears. The gearbox is clearly not overheating as it is stone cold, not having run. I have tried charging the battery, adding a second battery in parallel (in case of fading battery causing the error). I have driven the vehicle 10-15km to see if the message disappeared when the vehicle warmed and the battery perked up. I have also checked the wiring to the sensor and there is no obvious break/short. When C164 is disconnected pin 1 in the feed side gives a short to earth (which it should) and pin 2 does not register on the Ohmmeter, which would indicate to me that there is no wiring short to earth in the feed to the connector. The sensor itself is giving a resistance of 0.9 Ohms when cold, and this does not change when placed in a kettle which is boiled.
The circuit diagram in the electrical troubleshooting guide would suggest that the sensor thermo-switch is open when cold and closed when hot/overheated, which would be consistent with the very low resistance on the approximating a closed circuit and therefore triggering the alarm message. However, to my mind this would also mean that if the sensor was removed, thus leaving an open circuit, this should approximate to the open switch in normal conditions. But the overheat message still appears with the sensor removed!
So, my questions are: does the circuit need some (large)resistance from the sensor to indicate normal temperature? What is the normal resistance from the sensor when cold? And also when hot? And can I confirm that there is nothing else wrong by placing a suitable resistor in circuit to ensure the message goes away (before going to the trouble of importing a replacement)
Any suggestions welcome
Background: the vehicle (1998 4.6 HSE) has been standing for some time (2-3 weeks), has been started occasionally but not driven. Suddenly, just after Christmas, the gearbox overheat message appears. The gearbox is clearly not overheating as it is stone cold, not having run. I have tried charging the battery, adding a second battery in parallel (in case of fading battery causing the error). I have driven the vehicle 10-15km to see if the message disappeared when the vehicle warmed and the battery perked up. I have also checked the wiring to the sensor and there is no obvious break/short. When C164 is disconnected pin 1 in the feed side gives a short to earth (which it should) and pin 2 does not register on the Ohmmeter, which would indicate to me that there is no wiring short to earth in the feed to the connector. The sensor itself is giving a resistance of 0.9 Ohms when cold, and this does not change when placed in a kettle which is boiled.
The circuit diagram in the electrical troubleshooting guide would suggest that the sensor thermo-switch is open when cold and closed when hot/overheated, which would be consistent with the very low resistance on the approximating a closed circuit and therefore triggering the alarm message. However, to my mind this would also mean that if the sensor was removed, thus leaving an open circuit, this should approximate to the open switch in normal conditions. But the overheat message still appears with the sensor removed!
So, my questions are: does the circuit need some (large)resistance from the sensor to indicate normal temperature? What is the normal resistance from the sensor when cold? And also when hot? And can I confirm that there is nothing else wrong by placing a suitable resistor in circuit to ensure the message goes away (before going to the trouble of importing a replacement)
Any suggestions welcome