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Hi, I have a Volvo 940 GL Auto Estate 1986 Automatic registered 1992 (J). We are having problems with the button on the side of the gear selector which switches the car between 3rd and 4th speeds (I believe). I can be driving along quite normally when suddenly and for no apparant reason, the indicator arrow on the dashboard comes on and the transmission starts operating as a 3 speed unit. The result of this is a horrible vibration throughout the car and the engine seems to be labouring. We have tried to dpress the button to stop this and sometimes it works but more often it doesn't. Can anyone please help us out with this problem as it's driving me mad. Also, the drivers door won't shut properly now, it comes open a fraction whilst driving sometimes and I have to stop and very very gently close the door, if I slam it it just reverts to the slightly open position. Any help or advice would be most useful. Thank you in anticipation.

 

The problem with the overdrive could be the relay, wiring, switch or the od solenoid on the transmission. Go for the relay first, it is the easiest. Try removing and re-inserting it to see if it is just making bad contact. It is the tall white 1 inch square relay in the relay bank in the middle row behind the access for the fuses in the center consol. If that does not do it, a new one may be in order. A lot of times the solder traces and/or connections on the circuit board will crack, and they can be disassembled and fixed by re-flowing the solder. If that does not do it, then the wiring and switch would have to be tested. If they are good, then the solenoid is bad.
The problem with door might just be a loose strike or hinges. Check to see if any are loose, if not they will have to be re-adjusted which is sometimes a trial and error process to get it right.