GMC_DUDE

In another thread (now closed) someone was asking about crank relearn. In a nutshell it is this: One of the requirements of OBDII is that the PCM must detect and report misfire conditions. So how do you detect misfire? Well, the way GM does it is to monitor the time between the crankshaft sensor pulses and the camshaft sensor pulses. Since there is always some slack in the camshaft drive train, the time spaces will be one value if the cylinders are firing and the piston is delivering power, and another value if there is misfire and the piston is just coasting along. However, as you can imagine, every engine has a different amount of slack, so these timing gaps have to be calibrated, or "learned", into the PCM. The PCM has a routine in its software to do this, and the routine can be triggered by a command from HPTuners or the GM TECH 2.

So what's up with the relearn? Well, certain parts changes, i.e. new cam, new timing chain or gears, etc., can change the amount of slack, and the PCM has to relearn the gap values. The thread in question was discussing a custom PCM tune. Not sure how that would monkey up the works, though. Maybe someone else can explain.

Anyway, hope this quick and dirty explanation helps.

02sierraz71_5.3

iTrader: (2)

Is it possible for the cam learn procedure to be responsible for a vehicle not starting?

one03sierra

iTrader: (1)

ATTENTION: Your vehicle may not start unless this procedure is performed.

GM introduced an anti-theft system in 1996 and newer vehicles.

In order for your vehicle to start, you must perform the passkey relearn procedure.

If your vehicle’s battery is low, it is recommended a battery charger be hooked up at this time.

This Procedure will take approximately 20-30 minutes.



After your PCM is installed, please perform the following.

You may want to be outside your vehicle so shut the door, roll down the window.



PROCEDURE:



Insert key, attempt to start the vehicle and leave the key in the ON position.
In some vehicles, the Battery and Security light will blink for several seconds, and then shut off. Then the Security light will then remain ON. Leave the ignition ON until the Security light goes OFF. This will take more than 5 mins.

When the Security light goes OFF, turn the ignition to the OFF position.
Leave ignition OFF for 20 Seconds.

Attempt to start the vehicle again and leave the key in the ON position.
In some vehicles, the Battery and Security light will blink for several seconds, and then shut off. Then the Security light will then remain ON. Leave the ignition ON until the Security light goes OFF. This will take more than 5 mins.

Turn the ignition to the OFF position for 20 Seconds.
Attempt to start the vehicle again and leave the key in the ON position.
In some vehicles, the Battery and Security light will blink for several seconds, and then shut off. Then the Security light will then remain ON. Leave the ignition ON until the Security light goes OFF. This will take more than 5 mins.

Once this entire procedure has been completed (three times) your vehicle will start on the fourth attempt.


Note: Some vehicles perform the relearn in a different sequence. You may notice your security light, battery light and abs light will alternate. Once the security light is left out of the sequence that is considered one step. Repeat the procedure two more times and on the fourth time your vehicle will start.

bart cox

The crank position relearn can be called a bunch of things.
Crank angle Relearn
Crank position Relearn
Crank variation Relearn
Case learn
Crankshaft learn
Crankshaft position variation learn..
cmpk relearn Ect.. every scanner calls it different. lol

This may be of some help
97-2003 Engine CASE learn procedure:

Turn the key to on position
Turn Tech II on
Select the Diagnostics Menu
Select Car Information (Year, Make, Engine, Etc.) (Make sure they enter 1998 as the year.) (Also you will be asked what type of product line/type. It is a single letter code. Which corresponds to the first letter in your VIN)
Select Special Functions.
Select Variable Crankcase Learn Procedure.
Follow On Screen Directions.
The Crankcase Learn Procedure is going to ask the Technician to do the following:

Put E-brake On.
Make sure car is in neutral or park.
Turn engine on
Rev Car to Rev Limiter (car will hit limiter at 3,000 RPM)
Wait about 5 seconds.
Rev Car to Rev Limiter (The car will this time hits about 5,500 to 6,000 RPM)
Wait about 5 seconds.
Car is done.
2004+ CASE learn procedure:

Turn the key to on position
Turn Tech II on
Select the Diagnostics Menu
Select Car Information (Year, Make, Engine, Etc.)
Select Special Functions.
Select Variable Crankcase Learn Procedure.
Follow On Screen Directions.
The Crankcase Learn Procedure is going to ask the Technician to do the following:
Put E-brake On.
Make sure car is in neutral or park.
Turn engine on.
Rev Car to Rev Limiter
Car is done.





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That is for someone with a tech 2. if they have a genisys or other Spx varient scanner.
you have to tell the scanner you truck is a 2002 or lower, that way the crank learn tab will show up.
so when you do pick 2002, then you go to special tests, then you go to engine controls, then you go to "crankshaft relearn" then you follow the instructions.

The reason for the relearn is for the missfire detection to be accurate. It is something that has to be done when useing a pcm that was not in your truck previously and had the case learn done on it. Even from the factory, each vehicle has to get this done to the computer/ motor it works with. All it does when you do a case learn is tell the computer where the cam and crank are at in relationship to each other durring the firing event. That way the pcm can Accurately detect a missfire down to an individual cyl.

white1

iTrader: (5)

It can also be done with the GM tech 1. I couldn't do mine with the Snap on scanner though.

OCBC

iTrader: (1)

Isnt that a security thing? What does that have to do with the crank position?

When I first originally had my pcm tuned, the truck threw a P0300 code (multiple misfire) From the explanation above, this would be from the crank timing. I sent my pcm back to the tuner and he said that it was due to the fact that the 04's were sensitive to that code. So, if I understand things coreectly, he probably increased the range that the sensors are at? Or he completely blocked that code? I never did a crank relearn. I dont think it can be performed with the pcm outside of the truck correct?

Thanks for the info.

bart cox

Crank re-learn has to be done in the vehicle (PCM needs to know where the reference point is on the crankshaft anf cam shaft) no other way around it.

Some tuners just delete the SES light for the crank relearn, but since its deleted you will not get and stored data to pull IF you start to get a misfire. The GM PCM will detect a misfire down to a single cylnder which is a good tool. If you run any Nox or have a blower on your Motor I would think that this is real important to know.

OCBC

iTrader: (1)

I would venture to thats a bad thing! Will a local mechanic shop know how to do this relearn? Whats the best way to get this done? I would like to have this thing correct.

Scrapin'4.8

iTrader: (3)

Does it absolutely have to be done? Or sometimes is everything right on?? And about how much does a GM dealership charge to do this and about how long does it take?

one03sierra

iTrader: (1)

what i posted above is what a lot of people need if there truck does not start or a few other little glitches.