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07 M8 knock sensor failure

Rixster

Rixster

Well-known member
Premium Member
So I just helped a friend install a rktek head on his 07 M8. The very second we started the sled it flashed the wrench and gave us the knock sensor failure code. Tried starting it with the sensor unplugged and the plugging it back in, no change. Must have unplugged it and plugged it back in 15 times with no change. Anyone else have this issue at one time or another?
 
is there a washer (locking plate) under the knock sensor...is it tighten right..??...is there a chance that disassembling everything and putting it back together that something is loose activating the knock sensor...example ypipe springs sending out a frequency..
 
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I will defiantly check it out in the morning. The plate is under it, There is a good chance that a pipe spring or something is causing some issues. It is code 21, so its not actually a knock code, but a knock sensor failure. Don't know if there is a difference.
 
yep your right..you know I had that code come up on me last year and put me in limp mode for abit each time till I restarted and it was because I wasn;t running my mix of higher octane with my regular fuel that ride and once I added the higher octane all was well..strange eh..



Number of Flashes Trouble
1-2
(Check Engine Light)
Failure in ignition coil.
1-6
(Check Engine Light)
Incorrect adjustment/failure in
APV cable.
1-7
(Check Engine Light)
Failure in exhaust temperature
sensor.
1-8
(Check Engine Light)
Failure in servomotor.
2
(Check Engine Light)
Failure in injector(s).
2-1
(Check Engine Light)
Failure in knock sensor.
2-3
(Check Engine Light)
Failure in knock control system.
4
(Check Engine Light)
Open or short circuit in barometric
pressure sensor.
5
(Check Engine Light)
Open or short circuit in intake air
temperature sensor.
6
(Check Engine Light)
Open or short circuit in water
temperature sensor.
7
(Check Engine Light)
Open or short circuit in throttle
position sensor.
Steady Flash
(Coolant Temperature Light)
Coolant Temperature Above 80°
C (176° F).
Constant On
(Coolant Temperature Light)
Coolant Temperature Above 93°
C (200° F).
Back
 
well that's the strange part...the code was a failure code .I thought it was 2/1 but it was actually two years ago not last year like I first thought..,.what fixed it was octane which was fixing a knock/det issue...
the limp mode was what the knock sensor system is supposed to do isn't it..??..but there seems to be no code indicated in the chart for low octane knock limp mode so could code 2/1 and 2/3 actually indicate and or initiate the det limp mode as well..??

or at least code 2/1= failure of knock sensor...that doesn't necessarily have to mean the sensor failed for good . Could it not mean that the current fuel situation is causing the sensor to fail which is only meant to fail as long as the bad fuel is preventing it from working normal and once the det is eliminated the codes clear..?? and then if something else rattling is causing the same or similar frequency as a knock it will do the same thing as what det would transmit.

So I guess what im try to say is that the failure code is just a warning code working properly for a fixable issue activating it..??
 
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knock sensor will not recognize detonation or knock below 6000 rpm, you must have a faulty sensor or wire / wire connection if ecu 21 is on at start up. Have seen this before. Its a 2 stage knock system on this model, ecu 21 is recognizing knock and SLIGHTLY changing timing and fuel trying to fix deto, and ecu 23 is full retard on timing and adds lots of fuel and goes to limp mode.
 
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I'm sure this was considered - if the new head requires running higher octane, is the higher octane mixture in the fuel tank and has it had sufficient time to get thru the fuel system while the engine is running?
 
Coldfinger said:
I'm sure this was considered - if the new head requires running higher octane, is the higher octane mixture in the fuel tank and has it had sufficient time to get thru the fuel system while the engine is running?
Click to expand...

This did cross my mind, The fuel in the tank is old 91 from last year. So it is probably garbage. Along with checking other things the tank is going to be drained and fresh 91 put in it.
 
I don't know any other way to see a code unless you start it up. Please explain.

I'm just thinking, if it worked before the mod, and now it isn't, I'm thinking unlikely anything failed unless it wasn't installed properly or mishandled when off. Maybe these units are sensitive and can be damaged by removal, I don't know.

On the fuel idea - maybe 87 is the oem octane, in which case I'd think 91 would be sufficient. If it is a high compression head, that usually means you'll need to run higher octane. Not sure what your sled requires. I know my 2010 requires 91 at sea level but I can get away with 87 at 10,000. Fresh fuel is a good idea and won't cost anything to try.
 
Coldfinger said:
I don't know any other way to see a code unless you start it up. Please explain.

I'm just thinking, if it worked before the mod, and now it isn't, I'm thinking unlikely anything failed unless it wasn't installed properly or mishandled when off. Maybe these units are sensitive and can be damaged by removal, I don't know.

On the fuel idea - maybe 87 is the oem octane, in which case I'd think 91 would be sufficient. If it is a high compression head, that usually means you'll need to run higher octane. Not sure what your sled requires. I know my 2010 requires 91 at sea level but I can get away with 87 at 10,000. Fresh fuel is a good idea and won't cost anything to try.
Click to expand...

I dont know about mishandling but, it did get set in the magnetic bolt/nut bowl with everything else. I wonder if the magnet jacked it up somehow ?
 
Coldfinger said:
I don't know any other way to see a code unless you start it up. Please explain.

I'm just thinking, if it worked before the mod, and now it isn't, I'm thinking unlikely anything failed unless it wasn't installed properly or mishandled when off. Maybe these units are sensitive and can be damaged by removal, I don't know.

On the fuel idea - maybe 87 is the oem octane, in which case I'd think 91 would be sufficient. If it is a high compression head, that usually means you'll need to run higher octane. Not sure what your sled requires. I know my 2010 requires 91 at sea level but I can get away with 87 at 10,000. Fresh fuel is a good idea and won't cost anything to try.
Click to expand...

Yes, it is obvious you need to start the sled before reading codes.
Knock system dont work BELOW 6000rpm. So if a det code appears at idle after start up, it is something wrong with the sensor.

Daltech
 
I am having the same issue with my 07 M8 and have changed out the sensor with no change in the code.The sled runs fine with the code flashing. I have checked the torque of the sensor and the wiring. Some people think that it may be the ECU. I hope that it is not the ECU, they want $1800 for a new one. Any help with this would be apperciated.
 
911 said:
I am having the same issue with my 07 M8 and have changed out the sensor with no change in the code.The sled runs fine with the code flashing. I have checked the torque of the sensor and the wiring. Some people think that it may be the ECU. I hope that it is not the ECU, they want $1800 for a new one. Any help with this would be apperciated.
Click to expand...

don't ever pay that price...lots for sale in the swapmeets 350ish..
I bought a spare for the shelf..and the triangle/circle and square is said to be interchangeable as only approx. 3 percent difference fuel delivery

ps...one time I had the code on with no issues and I found a spark plug cap loose on one of the plugs and when I pushed it on securely all was fine..strange little gremlins with these electronics...haha
 
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