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Fluid Pressure, Check
It is extremely important for trouble-shooting that
the fluid is at the pressure required for correct functioning of the
automatic transmission. Therefore, carry out the following transmission fluid
pressure check:
· Vehicle must be horizontal and parking brake
engaged.
· Ensure that transmission fluid level is correct
(section 5.1). Switch off engine.
· In TECH 1 mode F0:DATA LIST, select parameters
"PRESS. REG. SOL." and "CALCULAT. PRESS.". Parameter
"PRESS. REG. SOL." indicates the current consumption of the
pressure regulator.
· Remove closure bolt and connect Fluid Pressure
Gauge KM-498-B using Adapter KM-580 or KM-498-4.
(Illustration E 4151 shows the
connection for AF 13).
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AF 14/20/22 as of MY 93.5: the main pressure is
measured at the pressure connection for brake B 4.
(Illustration C 9931 shows the connection for AF
14/20/22)
· Bring engine to operating temperature and then
allow to idle.
· Pressure check at idle speed:
Depress brake pedal and run transmission in the
various modes (economy/ sport/winter programs) and selector lever positions,
as specified in the following table. Read off the pressure regulator's
current consumption from TECH 1 and the transmission fluid pressure from the
pressure gauge/TECH 1 and compare with the relevant values in the following
table:
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Transmission mode
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Selector lever position
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Main pressure
(pressure gauge/TECH 1)
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Current consumption
(TECH 1)
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Economy
/ sport
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(AF
14/20/22)
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D, 3, 2
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3.7 to 4.3 bar
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varies
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Winter
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(AF
14/20/22)
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D
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3.7 to 4.3 bar
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approx. 970 mA
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Economy
/ sport / Winter
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(AF
14/20/22)
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R
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6.2 to 7.2 bar
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approx. 970 mA
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Economy
/ sport
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(AF
13)
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D, 3, 2
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3.9 to 4.3 bar
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varies
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Winter
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(AF
13)
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D
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3.9 to 4.3 bar
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approx. 970 mA
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Economy
/ sport / Winter
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(AF
13)
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R
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5.5 to 6.4 bar
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approx. 970 mA
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· Pressure check at idle speed:
TECH 1 can be used for the following additional check
(Actuator Test):
Engine running at idle speed, depress brake pedal and
put selector lever in position "N". Press key F5 (Actuator Test) in
TECH 1 main system menu, use arrow keys to select test
"PRESS.REG.SOL." and confirm with "YES".
After the "YES" key is actuated, the
pressure regulator is first activated at 911 mA. The pressure gauge must adjust
to a fluid pressure of approx. 3.0 to approx. 4.6 bar.
When the "YES" key is actuated again, the
pressure regulator is activated at 250 mA. The pressure gauge must now adjust
to a fluid pressure of approx. 12.4 to approx. 13.9 bar.
If
the values determined from the Actuator Test deviate from the nominal values,
carry out the following pressure check:
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Start engine.
Engage parking brake firmly.
Depress parking brake firmly.
Check idle speed (see table on the right).
Select selector lever position "D".
Read off main pressure from Pressure Gauge KM-498-B
(compare with following table).
Then perform the same check for selector lever
position "R".
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16 SV, 18 SV
C 18 NZ, Saloon
C 18 NZ, Estate
E 18 NVR
20 NE, C 20 NE, C 20 NEF with Motronic M 1.5
C 20 NE with Motronic M 1.5.1, Saloon
C 20 NE with Motronic M 1.5.1, Estate
C 14 NZ, 14 SE, C 14 SE, C 16 SE
C 16 NZ, X 16 SZ
C 25 XE
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800 to 850 rpm
750 to 910 rpm
650 to 810 rpm
770 to 870 rpm
720 to 880 rpm
770 to 930 rpm
620 to 780 rpm
820 to 980 rpm
750 to 910 rpm
620 to 780 rpm
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Transmission mode
|
Selector lever position
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Main pressure
(pressure gauge/TECH 1)
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Economy
/ sport/ Winter
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(AF
14/20/22)
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D
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3.7 to 4.3 bar
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Economy
/ sport/ Winter
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(AF
14/20/22)
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R
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6.2 to 7.2 bar
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Economy
/ sport / Winter
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(AF
13)
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D
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3.9 to 4.3 bar
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Economy
/ sport / Winter
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(AF
13)
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R
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5.5 to 6.4 bar
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If
the values for the pressure check are not attained, the possible fault can be
determined from the following table:
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Result of Check
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Possible Cause of Fault
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Main pressure higher than specified pressure range
in selector lever positions "D" and "R"
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· Pressure regulator defective
· Valve body defective (primary regulating valve)
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Main pressure lower than specified pressure range in
selector lever positions "D" and "R"
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· Pressure regulator defective
· Valve body defective (primary regulating valve)
· Fluid pump defective
· Brake B 4 defective (AF 14/20/22)
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Main pressure lower than specified pressure range in
selector lever position "D" only
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· Leak in fluid circuit for selector lever position
"D"
· Clutch C 1 defective (AF 14/20/22)
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Main pressure lower than specified pressure range in
selector lever position "R" only
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· Leak in fluid circuit for selector lever position
"R"
· Brake B 3 defective (AF 14/20/22)
· Clutch C 2 defective (AF 14/20/22)
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· Checking the stall speed
To
perform the following pressure check correctly, first check whether the stall
speed can be attained. To do this, proceed as follows:
Start engine.
Engage parking brake firmly.
Depress brake pedal firmly.
Select selector lever position "D".
Increase engine speed until value required for stall
speed of 2450 ± 200 rpm is attained.
This test must not last longer than 5 seconds, as it
heats the transmission fluid excessively.
Check temperature with TECH 1 (F0:DATA LIST test step
no. 18): nominal value 60 to 80 °C/140 to 176 °F. If the transmission fluid
temperature deviates from these nominal values, leave vehicle to idle (selector
lever position "N") until the nominal value is set again.
Thereafter, perform the same check for selector lever
position "R". The correct value for the stall speed is 2450 ± 200 rpm
here as well.
If
the values for the stall speed are not attained, use the following table to
determine the possible cause:
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Result of Check
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Possible Cause of Fault
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Engine speed higher than 2250 rpm in selector lever
position "D" and "R"
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· Poor fuel quality
· Fault in engine management system
· Stator overrunning clutch functions incorrectly
in converter
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Engine speed higher than 2650 rpm in selector lever
position "D"
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· System pressure is too low
· Clutch C 1 slips
· Overrunning clutch F 3 functions incorrectly (AF
14/20/22)
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Engine speed higher than 2650 rpm in selector lever
position "R"
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· System pressure is too low
· Reverse gear clutch slips (AF 13)
· Clutch C 2 slips (AF
14/20/22)
· Brake B 2 slips (AF 13)
· Brake B 3 or B 4 slips (AF
14/20/22)
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Engine speed higher than 2650 rpm in selector lever
position "D" and "R"
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· System pressure is too low
· Brake B 4 slips (AF
14/20/22)
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· Pressure check at stall speed
Engage
parking brake, depress brake pedal firmly, increase engine speed until stall
speed is attained and run transmission in the various programs
(economy/sport/winter) and selector lever positions "D" and
"R" as specified in the following table.
The
current consumption of the pressure regulator is measured by TECH 1 (F0:DATA
LIST parameters "PRESS. REG. SOL." and "CALCULAT. PRESS."),
the transmission fluid level is determined by Pressure Gauge KM-498-B in
conjunction with the corresponding adapter and TECH 1 and compared with the
relevant values in the following table:
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Transmission mode
|
Selector lever position
|
Main pressure
(pressure gauge/TECH 1)
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Current consumption
(TECH 1)
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Economy
/ sport / Winter
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(AF
14/20/22)
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D, 3, 2 ,1
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11.4 to 13.6 bar
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approx. 100 to 200 mA
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Economy
/ sport / Winter
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(AF
14/20/22)
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R
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17.0 to 20.5 bar
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approx. 100 to 200 mA
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Economy
/ sport / Winter
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(AF
13)
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D, 3, 2 ,1
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11.0 to 12.7 bar
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approx. 100 to 200 mA
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Economy
/ sport / Winter
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(AF
13)
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R
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14.4 to 17.2 bar
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approx. 100 to 200 mA
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If
the values for the pressure check are not attained, the possible fault can be
determined from the following table:
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Result of Check
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Possible Cause of Fault
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Main pressure higher than specified pressure range
in selector lever positions "D" and "R"
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· Pressure regulator defective
· Valve body defective (primary regulating valve)
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Main pressure lower than specified pressure range in
selector lever positions "D" and "R"
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· Pressure regulator defective
· Valve body defective (primary regulating valve)
· Fluid pump defective
· Brake B 4 defective (AF 14/20/22)
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Main pressure lower than specified pressure range in
selector lever position "D" only
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· Leak in fluid circuit for selector lever position
"D"
· Clutch C 1 defective (AF 14/20/22)
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Main pressure lower than specified pressure range in
selector lever position "R" only
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· Leak in fluid circuit for selector lever position
"R"
· Brake B 3 defective (AF 14/20/22)
· Clutch C 2 defective (AF 14/20/22)
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Note:
Under
the conditions specified, the engine runs at stall speed (higher than 1500 rpm,
normally approx. 2450 ± 200 rpm). As the conditions of this check very rapidly
heat the transmission fluid excessively, do not perform the individual
test steps for longer than 5 seconds each. If necessary, allow time for
the transmission fluid to cool down. (Description, see "Checking the Stall
Speed").
· After checking, remove Fluid Pressure Gauge
KM-498-B and Adapter KM-580 or KM-498-4, insert new closure bolt and tighten to
a torque of 14 Nm/10 lbf. ft.
· If the pressure checks indicate that the automatic
transmission is functioning incorrectly, the transmission must be removed and
disassembled or replaced.
The following transmission components should be
checked for defects/wear:
- Fluid pump
- Valve body with pressure regulator
- Fluid filter
- Fluid screen of pressure regulator
- Pressure limiting valve
- Connection ducts between components
- In addition, observe the notes in the
Trouble-shooting Table for Mechanical / Hydraulic Faults (section 5.3.2).
For
all adjustment/repair operations, see the corresponding Service Instructions.
For the AF 13 and AF 22, only external sealing work and replacement of the
solenoid valves and valve body with the pressure regulator should be carried
out in the first year after production. Additionally, the temperature sensor
wiring harness can be replaced on the AF 13. Disassembly and assembly of the AF
13 will be included in the relevant Service Instructions at a later date.
