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S90 1997 S90 elec/computer gremlins

Hi everyone,

My much loved S90 is doing/not doing a few things...

When I start, the temp gauge immediately goes to the warm driving level. (Also needs more cranks than usual).

The low-speed fan comes on/goes off as normal. However, the slightest press of the accelerator has revs dying.

That stops after it has warmed up a bit. Car then behaves normally with the exception of the Transmission warning light coming on sometimes - car still gets me home. After a few days/drives the Trans light goes off.

When I stop the hi-speed fan comes on for about 6 mins then goes off - it's never done that before. With colder Mtn temps here it's playing havoc with my battery! If I leave the Hi-speed relay plug in then the fan is on the whole time while driving. People sure hear me coming!!

What I have done so far:

  • Replaced the relay for the fans.
  • Changed the water temp sensor (admittedly with a used one).
  • About to replace the thermostat today.
  • Had all elec connections on the transmission cleaned and sealed as getting continual Trans faults like "Speed Sensor A"
  • Does this give anyone a few light bulbs going off??
  • As I live 30 klms out of any town I'm getting more than a tad concerned!! :)
  • Thank you for having a look at this....


  • Which sensor did you replace? There is one under the thermostat housing and one at the back of the engine near the firewall (under the cam sensor). Both of them should be around 180-200ohm when the engine is at working temperature.

  • Hi and thank was the one in the thermostat housing. Didn't even know there was another, but I'll get the mech to check it out when he gets back from the desert <sigh>..... does that unit have a proper name so I can search in the meantime?

    Regards, Michael

  • This may be completely unrelated, but how old is the battery? And is the alternator charging? If so, how much?

  • Thanks for the reply.....

    I've only had the car a year, so don't know battery age - and no dates on it. But it IS having little oomph, so have de-sulphated and charged fully several times - seems ok for the moment. Alternator will check...What is your thinking? Do you suspect low power "tripping" computers??



  • KISS principle, keep it simple stupid. One of my favourite reminders

    if battery capacity too low, and or alternator charge output not high enough, it can cause many things to play up

    for piece of mind and to ensure you don’t have a no start in the future, put a new battery in. Then have the alternator tested

    then have all of the ground connectors serviced

    you would be surprised what a little preventative medicine (PM) can do

  • Ramrod....see?

    Some people DO listen :))

    Replacement battery ordered! H/duty too.....big sucker.....

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