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SL55 Loss of Power

6K views 10 replies 6 participants last post by  Vegasbenztech777 
#1 ·
Hello all, 2003 Sl55 40k miles.
Started engine yesterday, low coolant light comes on and goes off, check engine light come on and stays on. It idled fine, but when I try to accelerate engine revs extremely slow as if it has no power. I tried adding coolant, it took about a 1/4 of a gallon to fill. I still have the same results check engine light is still on and power is very low.

Does anyone know what the problem might be?
Thanks Joe
 
#4 ·
That code is for a low voltage condition in your throttle position sensor. What you really need is a STAR diagnostic to help narrow it down better. Maybe someone in your area has one they would be willing to come help you out. If you plan on keeping this car and doing maintenance yourself, this tool is a must on these cars. You can find them for just about $500 from Chinese sellers. I think there is a guy in Texas on this forum that builds systems too but they cost a little more.
 
#5 ·
I agree a Star scanner is the only way to go,

As far as the related components, the throttle body, or gas pedal itself can be the culprit, but you cant be sure without scanning.
 
#6 ·
Try to erase the error code (any auto parts store these days has OBDII reader for that), then see if power returns. I have similar problem due to the faulty accelerator pedal. Every time I push it to the floor car goes into power limited mode. I just restart the car at the first stop light and problem goes away till next hard acceleration. Replacement pedal assembly is waiting to be installed since November.
 
#7 ·
In case you are wondering, the throttle pedal cannot be fixed DIY. I've had to replace both pedals in my AMG cars.
Normally they fail when under full throttle, but work fine when putting around. The loss of power is called 'limp mode' and can be reset by stopping and restarting the car.

The electrical controller in the throttle pedal is a sealed unit, and can't be opened without breaking something. I tried, since it was junk anyway, but found nothing servicable (see picture).
eBay replacement is possible to save a few bucks, but these are limited life items on the SL, and for that matter most MB cars.
 

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#9 ·
Even the potentiometer type, they are sealed, so you almost never get problems with oxidization, or embedded dirt, the problem is typically chafed carbon print, from the wiper going back and forth, and eating all of graphite away

Neither is repairable, not reliably at least...
 
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