General motors vehicle computer relearn procedures

GENERAL MOTORS VEHICLE COMPUTER RELEARN PROCEDURES

Performing any of the following repairs may require you to initiate a computer relearn procedure in order to restore proper vehicle operation.

Powertrain Control Computer replacement with a nontransferable PROM
Powertrain Control Computer reprogramming
Body Control Computer
Instrument Cluster replacement
Engine replacement
Crankshaft replacement
Crankshaft harmonic balancer replacement
Crankshaft position sensor replacement
Diesel Engine controller
Diesel engine PCM with or without injection pump replacement
Diesel engine front cover replacement.

Here are some helpful tips to perform the system relearn, depending upon the particular repair that you have performed.

Powertrain Control Computer Replacement with a nontransferable PROM

All computers being replaced must be reprogrammed or “reflashed”. This is so the replacement computer has the most up-to-date information for that particular vehicle. This information is specific for the vehicle based on the vehicle identification number, and cannot be used on another vehicle, even though they may appear to be similar. Relearn procedures involve: Crankshaft Variation (CASE Learn), Engine Idle speed, Theft Deterrent password, and Transmission adaptive shift points.

Powertrain Control Computer Reprogramming

If diagnostics reveal that a reprogram or re-flash of the computer is necessary, relearn procedures involve:

Crankshaft Variation (CASE Learn), Engine Idle speed, Theft Deterrent password, and Transmission adaptive shift points. Body Control Computer &/or Instrument Cluster replacement Theft deterrent password relearn is necessary. Engine, crankshaft, harmonic balancer, and crankshaft position sensor. If any of the above items are replaced, then a Crankshaft Variation relearn is necessary.

RELEARN PROCEDURES

IMPORTANT: Please note that the Theft Deterrent Password Relearn must be performed first, otherwise the vehicle may not start.

THEFT DETERRENT PASSWORD RELEARN

General Motors uses three different types of vehicle theft deterrent systems in their cars and trucks manufactured from 1986.

They are:

1. Pass-key or Passkey 2 (PK2)
2. Passlock
3. Passkey 3 (PK3) or Passkey 3+

Instead of listing all of the vehicles and the systems that they use, we will simplify the identification process by taking a look at the vehicle ignition key (Refer to page 8 for key identification). There is one other system, referred to as VATS (Vehicle Anti-theft System) that is used by GM. This system is similar to Passkey, but since a relearn is not necessary, we will not elaborate on this system in this article. By referring to the chart and matching the correct key, you can safely identify the system that the vehicle uses, and, in turn, determine the correct relearn procedure. Just remember, that this article pertains only to those vehicles with a re-programmable or “re-flashable” PCM.


PASSKEY & PASSKEY 2

This system consists of: the Powertrain Control Module (ECM or PCM), Body Control Module (BCM) or Passkey theft deterrent module, and the ignition lock and key. In most cases, the theft deterrent duties are handled by a Passkey module. In those vehicles, if you are replacing a key, all you must do is match the resistance of the existing key that is in use. If you replace the theft deterrent module, then the module will learn the existing key resistance with the first start up sequence. At that point, the resistance is permanently memorized by the module, and can no longer be changed. No relearn is necessary. In this situation, the vehicle will start and run with no problem. If the vehicle won’t start, check your scan tool for a VTD (Vehicle Theft Deterrent) Fail-Enable Mode trouble code, or if the security light on the dash is illuminated. If you have this code, then the vehicle probably is equipped with a BCM, and you must perform a relearn.

The next section applies only to those vehicles that use a BCM.

For those vehicles that use a BCM, the BCM can learn the resistance value of the existing key by using the relearn process. In order for the vehicle to start, the BCM (as well as the Passkey module in other vehicles) must identify the resistor pellet in the key, then the BCM sends a password to the PCM. If this password matches the password stored in the PCM, the system enables fuel delivery. So you can see that if either the BCM or PCM are replaced, a relearn procedure is necessary. This same relearn procedure can be used if an ignition key with a different resistance value is used to replace the existing key. Before beginning the relearn, make sure there is a fully charged battery in the vehicle, and both the BCM and PCM are properly powered up and in communication with each other. Now you’re ready to initiate the relearn procedure.

1. First, insert the ignition key and turn the ignition switch to the “On” position (Do not start the engine). Leave the switch on for 11 minutes. The security light may flash or be on steady during this 11 minute period. Make sure the light is no longer on or flashing before proceeding to #2 .
2. Turn the ignition switch off for 30 seconds.
3. Turn the ignition switch to the “On” position (as in step #1) for 11 minutes again.
4. Turn the ignition switch off for another 30 seconds.
5. Turn the ignition switch to the “On” position for 11 minutes a third time.
6. Turn the ignition switch off for 30 seconds one final time.
7. Turn the ignition switch to the “On” position one final time and wait 30 seconds.
8. Attempt to start the engine. If the engine starts and runs normally, the relearn is complete. If the engine does not start, check for trouble codes and address them before attempting the relearn procedure again.


PASSLOCK

The Passlock system is designed to prevent vehicle operation if the key is not used to start the vehicle. The key, which does not contain a resistor will turn the Passlock lock cylinder. The Passlock lock cylinder will relay a resistance code to the instrument panel cluster (IPC). It does this by rotating a magnet past a stationary hall effect sensor, creating a resistance code. At this point the IPC will determine if the resistance code is correct and within an acceptable time frame. If the code is correct, the IPC will send a coded password to the powertrain control module (PCM). If the PCM receives the correct password, it will allow the fuel injectors to operate normally and the vehicle will start and run normally. If the correct resistance code from the lock cylinder is not received within the acceptable time frame, the vehicle will go into a short tamper mode during which the theft deterrent system will not allow the vehicle to operate for approximately 4 seconds. When this occurs, the security indicator will flash. After three consecutive failed tries, the system will enter into a long tamper mode. In this mode, the fuel injectors will be disabled for approximately 10 minutes, and the security indicator will be flashing. Please note that in any of the tamper modes, the vehicle may start, but it will quickly stall.

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The Passlock system is designed to prevent vehicle theft even if any of the theft deterrent parts are replaced. Passlock eliminates the need for the key mounted resistor. Parts that can no longer be replaced without the possibility of the system going into a tamper mode and prevent starting are: the lock cylinder, the instrument panel cluster (IPC), and the powertrain control module (PCM).

In order to initiate the relearn:

1. Hook up your scan tool to erase any of the passlock/vehicle theft deterrent trouble codes. If there are any other codes, note them before you erase them, so you may address them after the relearn has been completed.
2. With the ignition key in the “On” position from the code-clearing step, attempt to start the vehicle. At this point, if the vehicle starts, and the security light has not illuminated, a relearn is not necessary, and you’re done. If the vehicle starts and stalls, leave the key in the “Run” position and wait for the “Security” light to turn off. This will take approximately 10 minutes. At any time during this relearn, the light may flash or be on steady. If the ignition switch is turned off at any time during this relearn cycle that the security light is illuminated, the entire cycle must be restarted from the beginning. For most cars, one cycle will be sufficient for the relearn. If the vehicle will not start after the first cycle, then continue the process from step #3 to the end. Most trucks will require that you continue from step #3 to the end.
3. When the light turns off, turn the ignition switch to the “Off” position for approximately ten seconds.
4. Next, repeat steps 2 and 3 two more times for a total of three cycles. After the third time, the new code will be relearned on the next start attempt when the ignition switch is rotated from the “Off” position.
5. From the “Off” position, start the vehicle, observing the security light. If the vehicle starts and runs normally, and the security light is off, the relearn is complete. If the vehicle does not start, check for trouble codes before proceeding further.

PASSKEY 3 AND PASSKEY 3+

In this system, the vehicle theft deterrent functions are provided by the theft deterrent control module. There is a transponder embedded in the head of the key that becomes energized by the exciter coils in the ignition lock cylinder when the ignition switch is turned on. The energized transponder now transmits a signal containing a unique value to the theft deterrent control module. If the module accepts this value, then there is an additional communication that takes place between the module and the key. If the module and the key agree, then the module sends the fuel enable password to the PCM. If the PCM recognizes the password, then the vehicle starts and runs normally. If any of the communication between the module and the key is incorrect or the PCM does not recognize the password, then the fuel injectors are disabled. The ignition key is a normal looking key with no visible contacts as in the Passkey or VATS systems. The transponder is located in the key head. The transponder value is fixed and cannot be changed. These keys are usually identified by the letters PK3, or PK3+ stamped into the steel body. A relearn will be necessary if any of the following have been replaced: any key, the theft deterrent control module or the powertrain control module (PCM). When the theft control module is being replaced, the module will learn the existing keys immediately. However, the PCM must learn the new fuel enable password from the new module. If you are replacing a PCM with a PCM that has been used in another vehicle or has been remanufactured, then a relearn must be performed in order for the PCM to learn the fuel enable password. Keep in mind that when you perform a relearn on this system, all previously learned keys will be erased from the theft deterrent control module’s memory. Any additional keys may be relearned immediately after the first relearn has been performed by inserting the additional key and turning the ignition switch to the “On” position within ten seconds of removing the previously learned key.

In order to initiate the relearn process:

1. Insert a master key (black head) into the ignition switch.
2. Turn to the “On” position without starting the engine. The security light should illuminate and stay on.
3. Wait approximately 10 minutes or until the security light turns off.
4. Turn off the ignition switch and wait 5 seconds.
5. Repeat steps 2 through 4 two more times with the same key.
6. Turn the ignition off. The vehicle will now learn the key transponder information on the next start cycle.
7. Start the vehicle. If vehicle starts and runs normally, and security light is off, the relearn is complete.

If additional keys are to be relearned:

8. Turn the vehicle off.
9. Insert the next key to be learned and turn the ignition switch to the “On” position within 10 seconds of removing the previously used key.
10. Wait for the security light to turn off. It should happen quickly. You may not even notice the light come on, because it will learn the key transponder immediately.
11. Repeat steps 8 through 10 for any additional keys.

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CRANKSHAFT VARIATION RELEARN (CASE Learn)

”CASE” means: crankshaft angle sensor error. A crankshaft variation relearn must be performed if:

A diagnostic trouble code of P1336 is present.
The computer has been replaced or re-programmed.
The crankshaft position sensor has been replaced.
The engine, harmonic balancer, clutch, or flywheel have been: disassembled, removed, or replaced.
The crankshaft position variation learning feature enables the computer to compensate for part manufacturing tolerances. This allows the computer to accurately detect an engine misfire throughout the engine RPM range. The learning process is stored in the computer’s memory and does not have to be repeated unless one or more of the above conditions are present.


To perform the relearn, proceed as follows:

Connect a scan tool to make sure there are no trouble codes stored in the computer’s memory. If there is any power train trouble code other than P1336 (Crankshaft Position Variation not learned), the computer will disable the relearn function until the problem that aused the code has been eliminated. Also, make sure that the engine coolant (check it when the engine is cold) and oil levels are at an acceptable level.

1. Set the parking brake and block the drive wheels. Make sure that the hood is closed.
2. Start the engine and make sure that the engine coolant temperature is at least 158 degrees F. (70 degrees C.)
3. Turn the engine off for at least 10 seconds.
4. Select the crankshaft position variation learn procedure (CASE Learn)on your scan tool.
5. Make sure that the transmission is in Park. Start the engine.
6. Apply the brakes and hold the pedal firmly.
7. Follow the scan tool instructions.

Remember: That you are going to increase the engine speed to approximately 3000 RPM, 4000 RPM, or 5150 RPM. That’s the variation learn fuel cutoff RPM (depending upon the engine), and that it’s important to release the throttle when the engine RPM starts to decrease as a result of the fuel cutoff going into effect. Failure to do such will result in over revving of the engine, causing possible engine damage.

8. Once the engine has returned to idle, check the status of Diagnostic trouble code P1336. If the scan tool indicates that the CASE has been learned, the relearn procedure is now complete. If CASE has not been learned, check for the presence of other power train codes. If any exist, correct the problem, then repeat this procedure.

NOTE: If the Crankshaft Variation Relearn is not accessible through your scan tool (some truck applications 1998 & later), perform the relearn in the following manner:

1. Turn off all of the accessories. With the Air temperature sensor and Coolant temperature within 5 degrees (Centigrade) of each other, start the engine and let it idle in Park or Neutral for two minutes.
2. Accelerate the vehicle to 55 mph at part throttle. Cruise at 55 mph for 8- 10 minutes until the engine reaches operating temperature.
3. Cruise at 55 mph for another 5-6 minutes.
4. Decelerate to 45 mph without using the brakes, and maintain 45 mph for 1 minute.
5. Perform 4 deceleration cycles, without using the brakes, of 25 seconds each where no specific speed is necessary. Returning to 45 mph for 15 seconds in between deceleration cycles.
6. Accelerate to 55 mph and cruise for 2 minutes.
7. Stop the vehicle and idle for 2 minutes with the brake applied and the transmission in Drive (automatic trans.) or Neutral (manual trans.) with the clutch depressed. Refer to diagram A on page 8.

BASE IDLE RELEARN


The Computer will reset the idle air control valve whenever the ignition switch is turned to the “On” position, then to the “Off” position. However, before you return the car to the customer, it is best to bring the engine up to operating temperature in Park with the air conditioning off. Then, turn the air conditioning on. Next, turn the air conditioning off. Next, place the transmission selector in drive. Finally, with the car in Drive, turn the air conditioning on. That’s it!


EDIT: PDF with more info attached 5-13-13 Thanks Hog!

Ok, now I dont feel so bad about staying with OBD1...lol

Excellent info. A couple of notes: VATS disable is your friend. The crank relearn is NOT necessary unless a P1336 or P0315 code is thrown. (Yes, I know there are those out there who think it's required, but GM's own documentation says it MAY be required.) Reflashing the stock PCM should never require a crank relearn, so if possible always use the same PCM the crank sensor was paired with at the factory. You MUST set the parking brake! (I'm not sure where the signal for this comes from, but I do know the crank relearn will fail if you don't set it.)