1994 855T 143 code and drivability

azureblue · Post by **azureblue** » 31 Jan 2015, 17:36

I pulled a 143 code - "Front knock sensor signal" today. I'd like to ask if that would be causing reduced gas mileage. I notice the stock boost gauge will peak then pull back kind of quick, too, when I floor it. I would like to know if this would cause any other issues with the car. BTW, 93 octane, Volvo plugs gapped to 028. I wish I could get to it, but it's cold and I would like to be able to delay it for a week, if I could. I see that I need to check the wiring, and that will mean pulling the fan to get to the front sensor. I have looked around for info on this, and it seems that dirty connectors are the probable cause. But if there is anything else I should know about or tips, so I don't have to pull the fan and dig around behind the manifold, I would appreciate it...

One more thing - I use the under hood ODB1 to get the codes. Would I get more info out of the OBD2 port? I don't have a reader, but I can go to a parts store.....

Post by **Ozark Lee** » 31 Jan 2015, 18:17

There are a couple of versions of the knock sensors and the wiring harness is different. I think the original versions had individual connectors on the sensors and they were problematic. The current version has both sensors that go to a common plug and you have have to change both of them to retrofit it. The knock sensors will alter the fuel economy but you aren't going to hurt anything by waiting for warmer weather to change them.

What you need to do is determine which style you have and then plan things out based on what is there and what you will need to modify. Removing the intake manifold makes the job about ten times easier so I would order a intake manifold gasket along with the sensors. The orientation of the sensors is also important.

The OBD-I codes on your car are actually a bit more accurate than are the OBD-II codes so using them for diagnostics is fine. The OBD-II is more convenient and it is easer to clear them using an OBD-II scan tool.

...Lee

azureblue · Post by **azureblue** » 01 Feb 2015, 09:27

Thanks - much appreciated. I was hoping it is the wiring. I kind of like electrical work. Maybe I can sort that out without having to pull the manifold. But it's been about 5 years since my PCV job, so I might as well plan on pulling the manifold in spring..

One more question about the knock sensors - would you know if are they Normally off switches?

Post by **Ozark Lee** » 01 Feb 2015, 09:34

Believe it or not they are microphones. They literally "listen" for knocks.

...Lee

azureblue · Post by **azureblue** » 01 Feb 2015, 09:56

So I was wondering if I could trace the wires and test for resistance or continuity without having to pull a bunch of stuff off the car. If they are microphones, then there be some sort of continuity /resistance there, so, if I can disconnect the sensors from the rest of the system, I should be able to trace back on the wiring to see if the is a break (bad connector) in the circuit.

2012 · Post by **2012** » 01 Feb 2015, 10:37

I've gotten this code before, used to happen all the time, not so much anymore. It's a hassle to keep resetting the light, but you have to consider many factors that could be setting off the "microphones". After I replaced my fuel pump the code hardly gets thrown , so that leads me believe anything that causes a disruption in ignition could set it off. The sensors are hardly ever the problem as you'll find plenty of people who have changed them to no avail. So, consider any ignition issues or fuel delivery first. Even fuel quality could factor in. Hope this helps and God bless.

azureblue · Post by **azureblue** » 01 Feb 2015, 10:52

One of those "chase the gremlin" things. Ack.. my least favorite...Thanks for the tip on the ignition - I'll check that out, too.