Why do a lot of Pro Tuners turn the P1336 enabler off?

P1336 is the Crankshaft Variance code. Is it's function mainly for EPA reasons?

Pretty sure it deals with if you put a bigger cam in it will cause the code to flip and come on.

"It doesn't relearn "automatically". It is a procedure you have to do with the Tech2. Many cals don't use it, most Vettes for example. If you swap PCMs you often have to run it again in the "new" vehicle. All new PCMs (running cals that use that test) need to have it done when installed initially. Tunring it off if sending out an exchange PCM prevents the guy having an SES light and not knowing what to do about it, or having to pay somebody (the GM dealer gets as much as $100.00) to do it. Try convincing a guy there is nothing wrong with the PCM, when all they can come back with is "my old PCM didn't turn the SES light on". They will often think you should pay for them having the relearn done. Most of the time it won't be required if the PCM has "learned" once, maybe 10% of the time it will need it again in another vehicle.
The vehicle will run fine either way, it causes no problems being shut off."

Answer from another thread.

Moved to "General" section.

Quote:

Originally Posted by onfire

P1336 is the Crankshaft Variance code. Is it's function mainly for EPA reasons?

It's function is for accurate misfire detection.

Changing the TC may cause this code.

Sometimes, the crank relearn does not work for some reason or other, so it's just easier to turn off the code than to deal with it.

More info...

Quote:

Originally Posted by GM Service Manual

DTC P1336

Circuit Description

The Crankshaft Position (CKP) sensor sends pulses to the PCM when the reluctor wheel teeth rotate past the CKP sensor. The PCM uses the CKP pulses in order to synchronize the ignition and the fuel injector operation, and in order to time the interval between each CKP pulse. The PCM determines when an excessive change in the crankshaft speed occurs by comparing each new time interval with the previous interval. A misfire causes an unexpected change in the crankshaft speed. A certain amount of acceleration or deceleration is expected between each firing stroke, but if the crankshaft speed changes more than an expected amount, the PCM interprets this as a misfire. The interval between CKP sensor pulses is extremely small. At high engine speeds, slight variations in the following components make misfire detection difficult:
The crankshaft
The reluctor wheel
The CKP sensor
The PCM learns variations during the Crankshaft Position System Variation Learning Procedure. The PCM compensates for these variations when it performs detect misfire calculations. Only a scan tool can command the PCM to perform the Crankshaft Position System Variation Learning Procedure again.
After the following actions, perform the learning procedure:
A PCM replacement
Any operation or repair involving the crankshaft, the CKP sensor, or the CKP sensor to reluctor wheel gap relationship.
An engine replacement
The ignition switch is in the ON position until the battery is drained.
Important

A PCM power disconnect with the ignition ON may erase the stored pulse value and set the DTC P1336.

Disconnecting the PCM will not erase the learned Crankshaft Position System Variation as long as the ignition switch is in the OFF position.

Important

Reprogramming the PCM does not require running the Crankshaft Position System Variation Learn Procedure unless the PCM is new or is from another vehicle.

A DTC P1336 sets if the Crankshaft Position System Variation is not within an acceptable range, or cannot be learned.

Conditions for Running the DTC

DTCs P0335, P0336, P0341, P0342, and P0343 are not set.

Conditions for Setting the DTC

The PCM has not learned the Crankshaft Position System Variation.

Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

Good info.

I may try a crank relearn with EFI LIVE just to see if it works.