Knock sensor question--93 850 GLT

My friend just got this car and the Check Engine light is on. The guy he got it from said he'd had the computer scanned and the message was to replace the knock sensor. However, the car isn't knocking, no matter what kind of gas is used. If the knock sensor in NG, shouldn't it knock?

Does the computer actually detect a bad sensor? Or is it merely indicating that it's time to change the sensor after a certain number of miles? If the sensor is actually bad, why isn't the car knocking? Is it possible that when the computer detects a bad sensor it retards the timing so the engine can't knock, in an effort to protect the engine?

Also, how does one clear the computer of such messages, to make the light go out?

Reply to
Dave M
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When the knock sensor is bad the ECU is runung the engine in a "limp home" mode. In this mode the engine can't knock, you get a terrible mpg ratio and the car won't run very fast.

It's detected. There is no "bad after so and so many miles" in a 93 Volvo.

Yep! see above.

There is a black box in the engine compartment, inside there is a button and a LED. You have to press the button a certain time and the error codes are a told via a blinking LED. To clear the error another timing of press/blink is needed. Google for swedish bricks or something like that to get a description how to do it.

You may remove the battery for half an hour to clear the codes but read

*all* the codes (there may be several!) before clearing and write them down. This way you can accertain that it's the knock sensor and compare codes if the Check Engine Light ever comes back.

Bye, Vitus (964, 1996)

Reply to
Vitus Jensen

There are 2 knock sensors on the 5 and 6 cylinders, and there was a TSB to update the wiring loom between them on the early 850's.

If you replace the sensors, beaware they must be torqued to a specific figure in order to work properly.

This could be your problem?

Tim..

Reply to
Tim..

Could be bad spark plug wires.Don't ask me how that kicks out bad knock sensor codes, but it did on my 94 850.

Reply to
JDG

Bad wire causing rough-running engine which might mimic gas knock?

Reply to
Dave M

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