Throttle Position Sensor Repair

Not too long after I bought my ST165 I started having drivability problems.  After a lot of head scratching I eventually traced it to the throttle position sensor.  This never gave any error codes unfortunately.

The fault was detected by using a multimeter.   It showed that there was no longer continuity between a couple of the pins.

Now I had the option of forking out for a new one,  spending far too much money on a used one or (as it was stuffed anyway) bashing it open.  Being an engineer I of course bashed it apart!

I don't have photos but the basic procedure follows:

1)   The top plate of the TPS (with the P/N on it) is held in with plastic fingers.  These should be cut off with a sharp knife.  

2)   The top plate can then be flicked off with a sharp screwdriver.  This reveals a rubber membrane.  Cut this membrane around the outer edge using a very sharp scalpel,  you will feel a solid flat surface below the membrane,  cut around the outer edge of it.  Tear the rubber away from above this flat surface.

3)   The flat white surface exposed is the ceramic circuit board.  There are four holes at one end,  these are the mount points for the pins.  There is a good chance that the solder joints holding these pins has failed resulting in no contact.  You can lever the other end of the plate up to see if the screened resistance tracks are still intact,  but be careful not to break the pins off!  To prevent pulling the tracks off the board be very careful lifting it up.  Ensure the solder is the problem,  if so it can be fixed.

4)   You have to solder the pins to the board on the same side as the pin.  But for best results you have to solder the pins with the board in place.  When installed,  the pins are on the inaccessible side of the board.  Er,  oops,  damn...?!  The small (~1mm) holes at the solder location are the key.  Before installing the board apply new solder to the pin,  and also to the solder pad.  Apply just enough to push them together.

5)   The trick is to get the heat to the other side of the board.  I used a thin piece of wire (paperclip or similar) held against the end of the pin to transmit the heat from the soldering iron.  Success is a matter of luck really.

At the end of the day,  if you don't succeed don't worry,  it was stuffed anyway   :-)

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