Knock sensor issue, resolved but how did it work?

[Towcar]

On the weekend I changed over my knock sensors and the loom. The sensors looked brand new, but the loom had a cracked plug on it, the rear one.

So I have had the check engine light coming on in my car regular as clock work. Every morning just as the engine gets up to operating temperature the check engine light came on P0327.

So what has me beat is why did it only come on when the car reached temperature? It would also go away after a while. I would say that since fixing the issue the car feels a lot better to drive.

Would the ECU pick up a voltage spike and " turn off " the faulty sensor relying on only the one? Does the car operate in closed loop while warming up then look for the knock sensor?

Don't get me wrong I am happy the have fixed the issue, and to have 2 x spare knock sensors in good nick to hock off!

 

[lout]

when cold, engine is in open loop, not using O2 sensors
when warmed up goes to closed loop, uses O2 sensors
i assume knock sensors are always monitored to adjust ignition timing but maybe not

 

[BlackVXGTS]

DTC P0327 V6 PCM - LEFT HAND KNOCK SENSOR CIRCUIT FAULT

CIRCUIT DESCRIPTION:
The Knock Sensor (KS) system detects engine detonation. The PCM retards the spark timing based on the signals from the knock sensors. The knock sensors produce an AC voltage. The knock sensor voltages are an
input to the PCM. The amount of AC voltage produced is proportional to the amount of knock. An operating engine produces a normal amount of engine mechanical vibration (noise). The knock sensors produce an AC voltage signal from this noise. When an engine operates, the PCM learns the minimum and maximum frequency of the noise the engine produces. When the PCM determines that this frequency is less than or greater than the expected amount, a knock sensor DTC will set.

CONDITIONS FOR RUNNING THE DTC
• The engine has been running for more than 10 seconds.
• DTC P0325 is not set.
• The engine coolant temperature is greater than 35°C.
• The TP sensor signal is greater than 22%.
• The engine speed is greater than 1000 RPMs.

CONDITIONS FOR SETTING THE DTC
• There is no LH knock sensor signal or too high a knock sensor signal detected by the PCM for 3 seconds.

ACTION TAKEN WHEN THE DTC SETS
• The PCM illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the History Data.
• When DTC P0327 is set, and current, the PCM uses a default spark advance table.

CONDITIONS FOR CLEARING THE MIL/DTC
• The PCM turns the MIL OFF after the first ignition cycle that the diagnostic runs and does not fail.
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failure.
• Use a Tech 2 scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS:
If circuit 815 is not open or shorted to earth, the most likely cause is an open circuit in the PCM. It is possible that a faulty PCM could be the cause of the DTC P0327, and it should be replaced.

 

[Towcar]

Thanks BlackVXGTS, that does go some way to explaining why it did what it was doing.

Still not sure why the MIL went away after a few minutes driving.

I would have thought that the coolant temp was above 35degrees C quite quickly after starting the car, to me if seemed like once the thermostat opened it would register the fault.

When it says the "PCM uses a default spark advance table" does this mean retards the engine and runs slightly rich?

 

[BlackVXGTS]

Don't know how often the diagnostic runs after the initial DTC is set. If it runs periodically and the problem has disappeared it could turn off the MIL. This could indicate that you have some sort of intermittent wiring problem.

According to the workshop manual the PCM can retard timing by up to 15 degrees. No impact on the fuel system.

 

[Towcar]

Interesting, and I would agree except it happened like clock work, so it isn't really intermittent.

I suppose it is what is was, and I am certainly grateful it is fixed

Now my next problem, the car keeps spinning the wheels as soon as it hits 3,000 rpm when I floor it, I think the traction control is going to have a heart attack!