Automatic Transmission Diagnosis

AUTOMATIC TRANSMISSION DIAGNOSIS
Automatic transmission problems can be a result of poor engine performance, incorrect fluid level, incorrect linkage or cable adjustment, band or hydraulic control pressure adjustments, hydraulic system malfunctions or electrical/mechanical component malfunctions. Begin diagnosis by checking the easily accessible items such as: fluid level and condition, linkage adjustments and electrical connections. A road test will determine if further diagnosis is necessary.

PRELIMINARY DIAGNOSIS
Two basic procedures are required. One procedure for vehicles that are driveable and an alternate procedure for disabled vehicles (will not back up or move forward).

VEHICLE IS DRIVABLE
1. Check for transmission fault codes using DRB scan tool.
2. Check fluid level and condition,
3. Adjust throttle and gearshift linkage if complaint was based on delayed, erratic, or harsh shifts.
4. Road test and note how transmission upshifts, downshifts, and engages.
5. Perform stall test if complaint is based on sluggish acceleration. Or, if abnormal throttle opening is needed to maintain normal speeds with a properly tuned engine.
6. Perform hydraulic pressure test if shift problems were noted during road test.
7. Perform air-pressure test to check clutch-band operation.

VEHICLE IS DISABLED
1. Check fluid level and condition.
2. Check for broken or disconnected gearshift or throttle linkage.
3. Check for cracked, leaking cooler lines, or loose or missing pressure-port plugs.
4. Raise and support vehicle on safety stands, start engine, shift transmission into gear, and note following:
a. If propeller shaft turns but wheels do not, problem is with differential or axle shafts.
b. If propeller shaft does not turn and transmission is noisy, stop engine. Remove oil pan, and check for debris. If pan is clear, remove transmission and check for damaged drive plate, converter, oil pump, or input shaft.
c. If propeller shaft does not turn and transmission is not noisy, perform hydraulic-pressure test to determine if problem is hydraulic or mechanical.