Advanced automotive fault diagnosis Control relay Transmission

10.4.7 Automatic transmission –
stall test
To assist with the diagnosis of automatic trans-
mission faults a stall test is often used. The dur-
ation of a stall test must not be more than about
seven seconds. You should also allow at least two
minutes before repeating the test. Refer to manu-
facturer’s recommendations if necessary.
Warning
If the precautions mentioned are not observed,
the gearbox will overheat.
The function of this test is to determine the cor-
rect operation of the torque converter and that
there is no transmission clutch slip. Proceed as
follows.
1. Run engine up to normal operating tempera-
ture by road test if possible.
2. Check transmission fluid level and adjust if
necessary.
3. Connect a revcounter to the engine.
4. Apply handbrake and chock the wheels.
5. Apply foot brake, select ‘D’ and fully press
down the throttle for about seven seconds.
6. Note the highest rev/min obtained (2500 to
2750 is a typically acceptable range).
7. Allow two minutes for cooling and then
repeat the test in ‘2’ and ‘R’.
Transmission systems
259
Knowledge check questions
To use these questions, you should first try to answer them without help but if necessary, refer back to
the content of the chapter. Use notes, lists and sketches to answer them. It is not necessary to write
pages and pages of text!
1. Describe how to use a road test to diagnose a suspected CV joint fault.
2. Explain why a stall test may be used to diagnose automatic transmission faults.
3. List in a logical sequence, a procedure for checking the operation of an electronically controlled auto-
matic transmission.
4. Describe a procedure used to test for a slipping clutch.
5. Describe a series of steps that could be used to diagnose the source of a ‘rumbling’ noise from a trans-
mission system.

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