Workshop Manual

7A–18
AUTOMATIC TRANSMISSION (4L30–E)
Chart 9c: Coastdown Harsh Shift Or Clunk At 3–2 Downshift
Step
Action
Yes No
1 Check line pressure. Refer to Line Pressure Test in this section.
Was line pressure normal?
Go to Step 2
Use Chart 15b:
Possible Causes
of High Line
Pressure in this
section
2 Does DTC P1850 set?
Diagnose P1850
first
Replace band
apply solenoid
(PWM) (323)
Chart 10: Intermittent 4TH TO 2ND Gear Downshift At Steady Speed
Step
Action
Yes No
1 Check for consistent speed sensor reading with scan tool.
Was the reading correct?
Replace mode
switch for
intermittent
contact.
Go to Step 2
2 1. Check for wiring harness damage or short to ground. If OK, go
to (2) .
2. Check transmission speed sensor connections. If OK, go to
(3) .
3. Replace transmission speed sensor.
Was the replacement complete?
—
Replace speed
sensor.
Chart 11: Engine Flare At Shifting During Turning Only (Usually With Warm Engine)
Step
Action
Yes No
1 Check for oil leaks at transmission.
Was the problem found?
Replace
transmission oil
filter and gasket
—
Chart 12: Engine Flare During 1–2 Or 2–3 Shift
Step
Action
Yes No
1 Check line pressure. Refer to Line Pressure Test in this section.
Was line pressure normal?
Go to Step 2
Use Chart 15a:
Possible Causes
of Low Line
Pressure in this
section
2 1. Check for a stuck 1–2 accumulator valve (320).
2. Check for servo piston (106) leaks.
3. Check for a stuck band apply solenoid (323).
Was line pressure normal?
Repair or replace —