I have a check engine light on my 1994 850 Turbo (158,000 miles). I checked the codes and it says a bad or disconnected knock sensor. I have looked at the info on other posts and will try to clean connection or replace it if that does not work. My question is how long can I drive it like this without harm and how much is a new sensor.

Thanks.

I read other posts about knock sensor faults being cured by changing cap, rotor, plugs, and wires. Mine was due for a tune-up anyway and it fixed the fault. If it's time for a tune-up it might be worth a try.

i found this (older post)


Re: Knock sensors[ALL/1998] posted by Ira Blumberg on
Tuesday, 23 December 1997, at 10:26 a.m.

I am not sure about Volvo engine controls, but on Mitsubishi 2.0L turbo engines, the knock sensor is very important. The ECU continuously advances the timing until it detects slight knock and then backs off a bit. The ECU uses this algorithm up to an advance appropriate for about 110 octane. Thus, you always get better performance if you use better gas. A bad knock sensor will either cause terrible performance (if it registers a false positive), will endanger your engine with excessive advance (if it fails to register knock when present), or will cause your ECU to go into limp mode (again terrible performance) if failure is detected.

I would suggest replacing the sensor if it is bad. You could purchase one from a discount mail order place or even order one used.

--Ira
http://brickboard.com/ARCHIVES/1997DEC/6551.shtml


--
'After silence, that which comes closest to expressing the inexpressible is music' - Aldous Huxley

I replaced the knock sensor on my '94 turbo last spring at about 85K miles.
Cost: about $95 for replacement part from Volvo & about $200 labor. Make sure
you get the new, improved version as Volvo had a replacement that didn't work.
Evidently, knock sensor malfunction is quite common on the '94. Although my
car ran fine, I replaced it fairly quickly as you're not absolutely sure
what's going on inside the engine.
Good luck. Don in Denver

I will try the tuneup option first. Is the cap easy to get to?
Also do I have to disconnect the battery to reset the check engine light after I am done?
Thanks for your help.

I will try the tuneup option first. Is the cap easy to get to?
Also do I have to disconnect the battery to reset the check engine light after I am done?
Thanks for your help.

Here is a link to the only instructions I could find. Maybe it will help.
http://www.volvospeed.com/Repair/sparkplugs.htm

My check engine light went out by itself yesterday, go figure. Thanks for your suggestions, I will have the car tuned up next month anyhow.