PT-CAN

PT (Powertrain) CAN

Introduction

The PT CAN is the fastest CAN bus in the E65/E66. It is an existing bus system. PT CAN stands for powertrain CAN. It links all control units/modules associated with the powertrain. All the bus nodes are connected in parallel with one another. In contrast with the previous bus,(two-core twisted pair) it now has three wires. The third wire of the bus cable is used as the wake-up line and has nothing to do with the actual CAN bus function.

Voltage Level on the PT CAN







When the bus is inactive, the bus high and low levels are at 2.5 V.

When the bus becomes active, the CAN Low voltage level changes to low (1.5 V) and the CAN High level changes to high (4 V), thus representing logical 1.

PT CAN Terminal Resistors







The PT CAN uses two terminal resistors to establish the correct inductive and capacitive impedance in the communication lines. Two 120 Ohm resistors are located in the wire harness (no longer in the control units as on previous systems). The resistors are located:

- Behind the right front kick-panel trim.(A-pillar)
- Below the rear seat.

The resistance is measured by connecting the appropriate adapter to any of the modules on the PT-CAN and measuring resistance between CAN-H and CAN-L.

The measured resistance should be close to 60 Ohms.

Failsafe Characteristics

If the PT CAN goes into emergency mode it is no longer available for the engine control system. However, it can still provide communication between the other bus nodes even if:

- One of the CAN leads (cores) is broken-one of the CAN leads (cores) is shorting to ground.
- One of the CAN leads (cores) is shorting to the power supply B+.

"Wake-up" Lead in PT CAN Network

The PT CAN for the E65/E66 is now a three wire CAN, the third wire is a hard wire KL-15 signal used to wake up the powertrain control units. The "wake-up" lead has nothing to do with the actual PT CAN function. A wake-up telegram is still transmitted by the CAS via the ZGM PT-CAN as a CAN message.