The "Carter Motor" is a servo motor that sits on top of the
engine (Fig 1) and adjusts the throttle when the engine is cold.
It is controlled by a separate controller (a "driver
that is situated beside the
LIE computer (but is not part of it). I do not yet
know if a similar motor is present in the Murciélago or Gallardo.
Feedback would be appreciated on this! The reason it is called a
"Carter Motor" is that it is a servo motor made by a large
manufacture of servo motors called "Carter".
motor operates on the accelerator control for a certain time
only after engine ignition and is cold. The driver control unit acts as an
interface to the LIE computer to control the carter motor.
The operating principal of this device is co-related to the
time that passes from engine ignition and the different
temperatures picked up by the engine control sensors. The carter
motor uses these parameters to bring the accelerator opening to
a calculated value.
| Figure 1. Carter
This decreases as
time passes, and the accelerator control is released when the engine
reaches the correct rpm. If this motor fails, you will get a
"L-check engine " light, an OBDII reading "Random Misfire" as well as
difficulties keeping the engine turning over at low RPM's when it is
Figure 2 (below) shows a diagram of the motor (1) and its position on
The motor screws in or out the shaft (3) that pushes against the
accelerator leaver (2) thereby adjusting the engines air supply. When
the engine is cold on startup this shaft is full out opening up air to
the engine. When the engine is warm the shaft should wind back and leave
a 6-8 mm spacing away from the accelerator bar.
The carter motor can fail for a number of reasons. The motor itself
could burn out. There is a relay behind the passenger seat that controls
the motor could fail or the Carter motor controller itself could fail.
Lets look at each in turn.
To checkout the carter motor itself we need to remove it from the
car. Fortunately this is easy as it is attached by only two bolts
(Fig 3). The bracket for the motor can be removed if a replacement is
needed (Fig 5) because Lamborghini replacements do not supply the
bracket. Figure 7 shows the electrical socket that handles the
controls to this motor. It is a 4 pin socket. I will number the pins 1
to 4, with pin 1 indicated in figure 8. Note how the socket is clamped
in the vice via the bracket shown in figure 4. Pin 1 is on the opposite
side of the bracket. Within the socket pins 3 and 4 have a spacer
between them. Now very carefully attach a ground to pin 1 and a +12V
wire to pin 2. The motor should briefly start pushing out the connecting
rod. It should then stop. Now switch the ground and +12V leads.
The connecting rod should pull back in and the motor should then stop.
This process can be repeated any number of times. If the motor
does not move the rod you have a faulty motor.
A second type of carter motor problem is due to a controlling relay
that supplies power to the motor. This relay is located in a box behind
the drivers seat. Access to the box is simple Pull the drivers seat
forward full. Peal back the carpet And open the two screws that hold a
panel in place (Fig. 10). You also need to remove two screws that
hold the top of the panel in place (Fig. 11). This panel may be just a
sheet of Leather covered metal, It may have attached to it a speaker
(e.g. In a 1999VT), or it may have attached to it the DVD drive of the
navigational system (in my case here). Carefully remove the panel to
expose the fuse/relay box area (Fig. 12). On the back of the panel
you just removed is a diagram of the fuse and relays and what they are
for. Relay #5 is for the carter motor. Count 5 relays down
from the back of the car. That is relay #5. remove it and examine it. It
should not have any burn marks on it. Unfortunately you cannot see the
relay pole contacts so it is not possible to see if it is stuck open or
closed. The easiest way to check this relay is to substitute it
with relay #11 which controls the air conditioning compressor clutch.
Assuming that is working, if you switch the relays and there was a
problem with the carter motor relay, once switched the carter motor
should now work and the air conditioning compressor should not switch on
when it is set to cooler. There are several different relays in
this location. They are not all the same so be careful pulling them out.
The relays are standard Bosch car relays (Fig. 14). They have numbers on
If neither of the above tests yield results, then you may have a
problem with the "Carter Driver Control Unit" . This is a box that is
located beside the LIE computer unit (located behind the passenger
seat, Fig 15). This $500 unit is the brain for the Carter motor.
It is essentially a small box of diodes and solid state relays that
switch on/off the carter motor. While a real electronics expert could
de-solder and test the few common components in the unit, for the most
of us the best we can do is open the box (four screws one on each
corner) and look for any burns on the varnish that covers the
components. If you suspect the unit ,you can try the old electronic
trick of spraying Freon on the suspected component (Fig 16), and seeing if it affects the
carter motor function. If the motor now turns on/off that component may be at fault. The Lamborghini part number
for the complete Carter motor control unit is #001637825.
Finally if you have a problem with the Carter motor staying on after
the engine ignition is switched off -- a serious problem that will run
down a battery -- the fault may be with the throttle position sensor
(TPS). Please see Adjusting the TPS for more information on this point.
Removing Carter Motor
||Fig 4. Carter
Motor & Bracket
||Fig 5. Remove
carter motor bracket
Carter motor with bracket removed
Fig 7. Electrical
connections for motor
Fig 8. Pin 1 of 4 pin
socket is indicated
Fig 9. 12 volts to pins 1
& 2 activates motor
Fig 10. Remove two screws from
Fig 11 Remove top 2 screws on lid
Exposed fuse/relay box area
Fig 13. remove relay # 5
Fig 14. Relay #5