Hummer H2. Manual - part 40

COMPUTER RELEARN PROCEDURES 

Vehicles equipped with engine or transmission computers may require a relearn procedure after vehicle battery 
is disconnected. Many vehicle computers memorize and store vehicle operation patterns for optimum 
driveability and performance. When vehicle battery is disconnected, this memory is lost. The computer will use 
default data until new data from each key start is stored. As computer memorizes vehicle operation for each 
new key start, driveability is restored. Vehicle computers may memorize vehicles operation patterns for 40 of 
more key starts.  

Customers often complain of driveability problems during relearn stage because vehicle acts differently then 
before being serviced. Depending on type and make of vehicle and how it is equipped, the following complaints 
(driveability problems) may exist:  

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Harsh Or Poor Shift Quality  

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Rough Or Unstable Idle  

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Hesitation Or Stumble  

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Rich Or Lean Running  

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Poor Fuel Mileage  

These symptoms and complaints should disappear after a number of drive cycles have been memorized. To 
reduce the possibility of complaints, after any service which requires battery power to be disconnected, vehicle 
should be road tested.  

GENERIC COMPUTER RELEARN PROCEDURES 

Some manufacturers identify a specific relearn procedure which will help establish suitable driveability during 
relearn stage. These procedures are especially important if vehicle is equipped with and electronically 
controlled automatic transmission or transaxle. Always complete procedure before returning vehicle to 
customer. The following general procedures are to be used if driveability problems are encountered after power 
loss or battery has been disconnected. These procedures may provide an aid in eliminating these problems.  

Automatic Transmission 

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Set parking brake, start engine in "P" or "N" position. Warm-up vehicle to normal operating temperature 
or until cooling fan cycles.  

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Allow vehicle to idle for one minute in "N" position. Select "D" and allow engine to idle for one minute.  

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Accelerate at normal throttle position (20-50%) until vehicle shifts into top gear.  

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Cruise at light to medium throttle.  

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Decelerate to a stop, allowing vehicle to downshift, and use brakes normally.  

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Process may be repeated as necessary.  

Manual Transmission 

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Place transmission in Neutral position. 

 

1994 Lexus ES 300 

GENERAL INFORMATION Computer Relearn Procedures

  

 

1994 Lexus ES 300 

GENERAL INFORMATION Computer Relearn Procedures

  

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Ensure emergency brake has been set and all accessories are turned off.  

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Start engine and bring to normal operating temperature.  

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Allow vehicle to idle in Neutral for one minute.  

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Initial relearn is complete, and process will be completed during normal driving.  

 

1994 Lexus ES 300 

GENERAL INFORMATION Computer Relearn Procedures

  

GENERAL INFORMATION 

Drive Axle Noise Diagnosis 

UNRELATED NOISES 

Some driveline trouble symptoms are also common to the engine, transmission, wheel bearings, tires and other 
parts of the vehicle. Make sure that cause of trouble actually is in the drive axle before adjusting, repairing, or 
replacing any parts.  

NON-DRIVE AXLE NOISES 

A few conditions can sound just like drive axle noise and have to be considered in pre-diagnosis. The 4 most 
common noises are exhaust, tires, CV/universal joints and trim moldings.  

In certain conditions, the pitch of exhaust gases may sound like gear whine. At other times, it may be mistaken 
for a wheel bearing rumble.  

Tires, especially radial and snow tires, can have a high-pitched tread whine or roar, similar to gear noise. Also, 
some non-standard tires with an unusual tread construction may emit a roar or whine.  

Defective CV/universal joints may cause clicking noises or excessive driveline play that can be improperly 
diagnosed as drive axle problems.  

Trim and moldings can also cause a whistling or whining noise. Ensure that none of these components are 
causing the noise before disassembling the drive axle.  

GEAR NOISE 

A "howling" or "whining" noise from the ring and pinion gear can be caused by an improper gear pattern, gear 
damage, or improper bearing preload. It can occur at various speeds and driving conditions, or it can be 
continuous.  

Before disassembling axle to diagnose and correct gear noise, make sure that tires, exhaust, and vehicle trim 
have been checked as possible causes.  

CHUCKLE 

This is a particular rattling noise that sounds like a stick against the spokes of a spinning bicycle wheel. It 
occurs while decelerating from 40 MPH and usually can be heard until vehicle comes to a complete stop. The 
frequency varies with the speed of the vehicle.  

A chuckle that occurs on the driving phase is usually caused by excessive clearance due to differential gear 
wear, or by a damaged tooth on the coast side of the pinion or ring gear. Even a very small tooth nick or a ridge 
on the edge of a gear tooth is enough to cause the noise. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Drive Axle Noise Diagnosis

  

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Drive Axle Noise Diagnosis

  

This condition can be corrected simply by cleaning the gear tooth nick or ridge with a small grinding wheel. If 
either gear is damaged or scored badly, the gear set must be replaced. If metal has broken loose, the carrier and 
housing must be cleaned to remove particles that could cause damage.  

KNOCK 

This is very similar to a chuckle, though it may be louder, and occur on acceleration of deceleration. Knock can 
be caused by a gear tooth that is damaged on the drive side of the ring and pinion gears. Ring gear bolts that are 
hitting the carrier casting can cause knock. Knock can also be due to excessive end play in the axle shafts.  

CLUNK 

Clunk is a metallic noise heard when an automatic transmission is engaged in Reverse or Drive, or when throttle 
is applied or released. It is caused by backlash somewhere in the driveline, but not necessarily in the axle. To 
determine whether driveline clunk is caused by the axle, check the total axle backlash as follows:  

1. Raise vehicle on a frame or twinpost hoist so that drive wheels are free. Clamp a bar between axle 

companion flange and a part of the frame or body so that flange cannot move.  

2. On conventional drive axles, lock the left wheel to keep it from turning. On all models, turn the right 

wheel slowly until it is felt to be in drive condition. Hold a chalk marker on side of tire about 12" from 
center of wheel. Turn wheel in the opposite direction until it is again felt to be in drive condition.  

3. Measure the length of the chalk mark, which is the total axle backlash. If backlash is one inch or less, 

clunk will not be eliminated by overhauling drive axle.  

BEARING WHINE 

Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by malfunctioning pinion 
bearings. Pinion bearings operate at driveshaft speed. Roller wheel bearings may whine in a similar manner if 
they run completely dry of lubricant. Bearing noise will occur at all driving speeds. This distinguishes it from 
gear whine, which usually comes and goes as speed changes.  

BEARING RUMBLE 

Bearing rumble sounds like marbles being tumbled. It is usually caused by a malfunctioning wheel bearing. The 
lower pitch is because the wheel bearing turns at only about 1/3 of driveshaft speed.  

CHATTER ON TURNS 

This is a condition where the whole front or rear vibrates when vehicle is moving. The vibration is easily felt 
and heard. Extra differential thrust washers installed during axle repair can cause a condition of partial lock-up 
that creates the chatter.  

AXLE SHAFT NOISE 

Axle shaft noise is similar to gear noise and pinion bearing whine. Axle shaft bearing noise will normally 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Drive Axle Noise Diagnosis