Page 355 of 464
355 Practical hints
What to do if …
Symbol messagesDisplay symbol
Display message
Possible cause
Possible solution
# 
Battery/Alternator
Visit workshop
The battery is no longer charging. 
Possible causes:
Alternator malfunctioning
Broken poly-V-belt
Do not forget that the brake system 
requires electrical energy and may 
be operating with restricted capa-
bility. Considerably greater brake 
pedal force is required and the stop-
ping distance is increased.
Stop immediately and check the poly-V-belt.
If it is broken:
Do not continue to drive. Notify an au-
thorized Mercedes-Benz Center.
If it is in order:
Drive immediately to the nearest autho-
rized Mercedes-Benz Center. Adjust driv-
ing to be consistent with reduced 
braking responsiveness. 
     
        
        Page 356 of 464

356 Practical hintsWhat to do if …Display symbol
Display message
Possible cause
Possible solution
USA only:;Canada only:!
Release
parking brake
You are driving with the parking 
brake set.
Release parking brake (
page 49). 
2
Brake wear
Visit workshop
The brake pads have reached their 
wear limit.
Have the brake pads replaced as soon as 
possible.
3
Brake fluid
Visit workshop
There is insufficient brake fluid in 
the reservoir.
Risk of accident! Stop the vehicle and notify 
an authorized Mercedes-Benz Center. Do 
not add brake fluid! This will not solve the 
problem.
Warning!
G
Driving with this message displayed can re-
sult in an accident. Have your brake system 
checked immediately. Do not add brake flu-
id before checking the brake system. 
Overfilling the brake fluid reservoir can re-
sult in spilling brake fluid on hot engine 
parts and the brake fluid catching fire. You 
can be seriously burned.
!If you find that the brake fluid in the 
brake fluid reservoir has fallen to the 
minimum mark or below, have the 
brake system checked for brake pad 
thickness and leaks.
!Brake pad thickness must be visually 
checked by a qualified technician at the 
intervals specified in the Maintenance 
Booklet. 
     
        
        Page 357 of 464

357 Practical hints
What to do if …
During severe operating conditions and 
stop-and-go city traffic, the coolant tem-
perature may rise close to 248°F (120°C).Display symbol
Display message
Possible cause
Possible solution
Ï
Coolant
Stop, engine off
The poly-V-belt could be 
broken.
Stop immediately and check the poly-V-belt (
page 411).
If it is broken:
Do not continue to drive. Otherwise the engine will overheat 
due to an inoperative water pump which may result in dam-
age to the engine. Notify an authorized Mercedes-Benz 
Center.
If it is in order:
Do not continue to drive the vehicle with this message dis-
played. Doing so could result in serious engine damage that 
is not covered by the Mercedes-Benz Limited Warranty. 
Drive immediately to the nearest authorized 
Mercedes-Benz Center.
Observe the coolant temperature display (
page 122).
!The engine should not be operated with 
the coolant temperature above 248°F 
(120°C).
Doing so may cause serious engine 
damage which is not covered by the 
Mercedes-Benz Limited Warranty. 
     
        
        Page 358 of 464

358 Practical hintsWhat to do if …Display symbol
Display message
Possible cause
Possible solution
Ï
Coolant
Stop, engine off
The coolant is too hot.
Stop the vehicle and turn off the engine.
Only start the engine again after the mes-
sage disappears. You could otherwise dam-
age the engine.
/
Coolant
Check level
The coolant level is too low.
Add coolant (
page 293).
If you have to add coolant frequently, have 
the cooling system checked by an autho-
rized Mercedes-Benz Center.
Warning!
G
Driving when your engine is badly overheat-
ed can cause some fluids which may have 
leaked into the engine compartment to 
catch fire. You could be seriously burned.
Steam from an overheated engine can cause 
serious burns and can occur just by opening 
the hood. Stay away from the engine if you 
see or hear steam coming from it. Turn off 
the engine, get out of the vehicle and do not 
stand near the vehicle until the engine has 
cooled down.
The engine should not be operated with the 
coolant temperature above 248°F (120°C). 
Doing so may cause serious engine damage 
which is not covered by the Mercedes-Benz 
Limited Warranty.Warning!
G
Do not spill antifreeze on hot engine parts. 
Antifreeze contains ethylene glycol which 
may burn if it comes into contact with hot 
engine parts. You can be seriously burned.
!Do not ignore the low engine coolant 
level warning. Extended driving with 
this message and symbol displayed 
may cause serious engine damage not 
covered by the Mercedes-Benz Limited 
Warranty.
Do not drive without sufficient amount 
of coolant in the cooling system. The 
engine will overheat, causing major en-
gine damage. 
     
        
        Page 359 of 464

359 Practical hints
What to do if …
Display symbol
Display message
Possible cause
Possible solution
±
Display malfunction
Visit workshop
Certain electronic systems are un-
able to relay information to the con-
trol system. The following systems 
may have failed:
Coolant temperature display
Tachometer
Cruise control display
Have the electronic systems checked by an 
authorized Mercedes-Benz Center.
G
Display malfunction
Visit workshop
The instrument cluster display is 
malfunctioning.
When the display is malfunctioning, warnings 
and malfunction messages might not be dis-
played.
Continue driving with added caution.
Visit an authorized Mercedes-Benz Center 
as soon as possible.
The displays for several systems 
have malfunctioned. Some systems 
themselves may also have malfunc-
tioned.
Continue driving with added caution.
Have the electronic systems checked by an 
authorized Mercedes-Benz Center.
J
Doors open
You are attempting to drive with 
one or more doors open.
Close all doors. 
     
        
        Page 360 of 464

360 Practical hintsWhat to do if …When the message 
Add 1 qt. 
(Canada: 
1 liter
) engine oil when next 
refueling (SLK 55 AMG) or 
Check oil 
level when next refueling (SLK 350) 
appears while the engine is running and at 
operating temperature, the engine oil level 
has dropped to approximately the 
minimum level.When this occurs, the warning will first 
come on intermittently and then stay on if 
the oil level drops further.
Visually check for oil leaks. If no obvious oil 
leaks are noted, drive to the nearest ser-
vice station where the engine oil should be 
topped to the required level with an ap-
proved oil specified in the Factory 
Approved Service Products pamphlet.
Display symbol
Display message
Possible cause
Possible solution
:
USA only:Add 1 qt. engine oil
when next refuelingCanada only:Add 1 liter engine oil
when next refueling
SLK 55 AMG only:
The engine oil level is too low.
Add engine oil (
page 292) and check the 
engine oil level (page 288).
Check oil level
when next refueling
SLK 350 only:
The engine oil level has dropped to 
a critical level.
Check the engine oil level (
page 288) and 
add engine oil as required (page 292).
If you must add engine oil frequently, have 
the engine checked for possible leaks.
!The engine oil level warnings should 
not be ignored. Extended driving with 
the symbol displayed could result in 
serious engine damage that is not 
covered by the Mercedes-Benz Limited 
Warranty. 
     
        
        Page 361 of 464
361 Practical hints
What to do if …
Display symbol
Display message
Possible cause
Possible solution
:
Engine oil level
Stop, engine off
SLK 55 AMG only:
There is no oil in the engine. There 
is a danger of engine damage.
Carefully bring the vehicle to a halt as soon 
as possible.
Turn off the engine.
Add engine oil (
page 292) and check the 
engine oil level (page 288).
Engine oil level
Visit workshop
SLK 55 AMG only:
The measuring system is malfunc-
tioning.
Have the measuring system checked by an 
authorized Mercedes-Benz Center.
Engine oil level
Reduce oil level
SLK 55 AMG only:
You have added too much engine 
oil. There is a risk of damaging the 
engine or the catalytic converter.
Have oil siphoned or drained off.
Observe all legal requirements with respect 
to its disposal.
Engine oil
Visit workshop
SLK 55 AMG only:
There may be water in the engine 
oil.
Have the engine oil checked. 
     
        
        Page 362 of 464
362 Practical hintsWhat to do if …Display symbol
Display message
Possible cause
Possible solution
A
Fuel reserve
The fuel level has dropped below 
the reserve mark.
Refuel at the next gas station (
page 284).
Check gas cap
See Operator’s Manual
The fuel cap may not be closed 
properly.
Check the fuel cap (
page 284).
If it is not closed properly:
Close the fuel cap.
If it is closed properly:
Have the fuel system checked by an autho-
rized Mercedes-Benz Center.
K
Lock retractable roof
The retractable hardtop is not 
locked properly.
Push the retractable hardtop switch forward 
or rearward until the retractable hardtop is 
completely closed or open (
page 237).
Retractable roof
Visit workshop
The retractable hardtop is 
malfunctioning.
Have the retractable hardtop checked by an 
authorized Mercedes-Benz Center.
O
Close hood
You are driving with the hood open.
Close the hood (
page 287).
F
Replace key
The SmartKey is malfunctioning.
Visit an authorized Mercedes-Benz Center.