Power supply, ground and bus communication

Fig 1: Identifying Power Supply, Ground And Bus Communication

Courtesy of SAAB-SCANIA OF AMERICA, INC.

POWER SUPPLY, GROUND AND BUS COMMUNICATION

Pin no.	Signal type	Description
1	Input signal	ECM turns on the Check Engine lamp by grounding the pin.
3	+30 supply	From instrument panel main fuse box (22) pin 35 via fuse 4.
4	Ground	Grounding points G43 and G34.
7	I-bus
8	I-bus

Line to ECM, petrol

Fig 2: Line To ECM, Petrol Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Line to ECM, diesel

Fig 3: Line To ECM, Diesel Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Power supply and ground

Fig 4: Power Supply And Ground Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

When the ignition is turned ON, the instrument will perform a lamp check and turn on the display under the speedometer. It will also light up the graduations if the cabin lighting is dim and the needles will rise from their rest positions.

CIM wakes up the main instrument unit when the key is inserted in the ignition switch by briefly applying B+ to the I-bus lead.

Communication can also be initiated when the key is removed from the ignition switch. This is done, for example, when the main beam signal is activated.

Another method of waking the main instrument unit when the ignition is OFF is to press the reset button. This will turn on the display and show the trip and odometer readings for 20 seconds, bus communication will not be initiated.