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Need Master Tech Help: CLK55 AMG

1860 Views 1 Reply 2 Participants Last post by  nrphlly
I started my car one morning and it idled higher and much longer than normal (2-3seconds). I drove to local store and upon restart the car went into “Limp Mode”
- Read ODB-II and got P0120- Throttle Pedal Sensor Circuit A
- I replaced the connector to the Throttle-Body as it has come loose before
- I replaced the entire Throttle-Body thinking the actuator sensor for the motor went bad.
- I reset the Check Engine light and started the car.
- The ECU stays in Limp Mode and the P0120 ODB-II error comes back.
The car is now at a MB dealer and they looked at MB codes through MB Diagnostic connector next to the ECU. They say the Throttle Peddle Sensor, that is the electrical sensor that is connected to a real-world cable up from the car’s interior throttle pedal reads OK and is within spec.
The computer seems to be ignoring the Throttle Body and thinks it is dead, even with a new one? As such, the ECU stays in Limp Mode.
Question1: should the tech be resetting the ESP “limp mode”, or is that mode automatically to turn off? Does the MB diagnostic have some form of “clear codes” like the ODB-II protocol?
Question2: I checked the two fuses for the Throttle Body within the engine bay fuse box and all are OK. Does the ECU have some fuse for the drive current to the throttle body motors?
Question3: I did see 5V at the connector for the Throttle Body feedback sensors, so I feel the return voltage is OK. Basically, the TB includes 3 potentiometers for feedback and two motor signals.
The car cranks and idles fine. If you manually move the interior pedal, it seems to want to increase RPM, which tells me that the TB is opening just a tiny amount. Or, the ECU is just adding a little gas.
What to test??? Could the ECU have gone bad?
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Maserati Quattroporte, Bespoke S55 AMG, E65 BMW 760li, Renntech CLK350, Hennessey Tahoe
1,105 Posts
I am not a master tech but.....

I had the same limp mode problem due to a faulty speed sensor in my transmission.. I myself, opened my own transmission and changed the valve body that tells the transmission when to shift. My 430 was still in limp mode and actually shifted alot worse...

"HENCE" this is because once a faulty component is changed the computer is reading the "New settings of that component still as faulty.....

I took my car to a shop that tried to clear my cars codes with an odb but you cant clear "HARD" codes in this manor.

I took it to an independent Mercedes specialist and they hooked my car up to a machine and IBM notebook. They ran a diagnostic with the car and it failed every test!!!!!

They cleared every code in the ecu and tcu, and.................................


Limp mode is a hard code that makes sure you get the "BUGGY" to the benz doctor before you kill her.

Have someone that "recognizes your knowlegde about your vehicle" clear the codes for you.... then see what comes back!!!!!!!

i hope this helps you out.... Please do let me know.......:thumbsup:
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