Step by step repair guide on how to troubleshoot and repair automatic transmission problems. This repair guide pertains to most vehicles.
Difficulty Scale: 4 of 10
Tools and Supplies Needed
Diagnostic Procedure Before Repair
Step 1 - Clear all DTC's with a engine scan tool (diagnostic trouble codes.) Visit - Scan PCM
Step 2 - Start the engine and observe the MIL, if it does not illuminate continue to next step (service engine soon or check engine light.)
Step 3 - Drive the vehicle while trying to maintain a constant throttle position as it accelerates up through all four gears. If the transmission is shifting properly, it should be in 4th gear by the time you reach 45 to 50 mph on level ground. Repeat this procedure from a standing start 3 to 5 times. Rescan the PCM for trouble codes, if none appear the problem could have been a onetime occurrence. If a trouble code has returned repair as needed and recheck system.
Problem Guide
Will not go into gear:
Goes into gear but fades out of gear or is slipping while driving:
Goes into gear but does not shift out of first gear:
Tips and Fixes
Fluid Level and Leaks A common complaint with automatic transmissions is them leaking fluid. Leaks
can occur from the output shaft seal, input shaft seal, pan gasket, fluid cooler
or lines. When adding transmission fluid, do not overfill, doing so could cause
the fluid to become aerated which will affect transmission operation. If the fluid level is low with no visible leaks, check the radiator for fluid
in the coolant. The cooler inside the radiator may be leaking and cross-contaminating
the radiator coolant (the coolant will be milky pink.) Also check the condition
of the fluid, some discoloration and darkening is normal as the fluid ages, but
if the fluid is brown or has a burnt smell its badly overused and a
transmission service
is needed. Most transmission problems can be prevented by changing the fluid and filter
(if applicable) according to manufacturer specifications. In extreme conditions
installing an aftermarket auxiliary cooler parallel can be installed furthering
the cooling effect. This prevents fluid overheating on vehicles used for towing
or performance applications. Helpful Information Automatic transmissions make specific noises when a malfunction occurs. An automatic
transmission is a hydraulic pressure driven system that can make different noises
than manual transmission problems. If the transmission filter becomes plugged due
to debris, it can make a whirring noise. If the fluid level is low, you might hear
a bubbling sound which is caused by the pump scavenging fluid inside the transmission
pan. Most internal failures are due to bearing, clutch or hard part failure. When
such a failure occurs the transmission can make a grinding, whirring sound or no
noise at all. When a transmission has a major failure you might hear a loud pop
which could mean a drive component inside the transmission has failed. Best Practices